diff --git a/tests/data/ar/Animal.php b/tests/data/ar/Animal.php
index 839e605d26..b2d842ddda 100644
--- a/tests/data/ar/Animal.php
+++ b/tests/data/ar/Animal.php
@@ -39,7 +39,7 @@ class Animal extends ActiveRecord
 
     /**
      * @param type $row
-     * @return \yiiunit\data\ar\Animal
+     * @return Animal
      */
     public static function instantiate($row)
     {
diff --git a/tests/data/views/widgets/ListView/item.php b/tests/data/views/widgets/ListView/item.php
index 8703566571..a100d07514 100644
--- a/tests/data/views/widgets/ListView/item.php
+++ b/tests/data/views/widgets/ListView/item.php
@@ -1,4 +1,7 @@
 <?php
+
+use yii\widgets\ListView;
+
 /**
  * @link https://www.yiiframework.com/
  * @copyright Copyright (c) 2008 Yii Software LLC
@@ -7,7 +10,6 @@
  * @var array|object $model
  * @var string $key
  * @var int $index
- * @var \yii\widgets\ListView $widget
+ * @var ListView $widget
  */
-
 echo "Item #{$index}: {$model['login']} - Widget: " . $widget->className();
diff --git a/tests/framework/ar/ActiveRecordTestTrait.php b/tests/framework/ar/ActiveRecordTestTrait.php
index f82db23a2e..2d92dceacf 100644
--- a/tests/framework/ar/ActiveRecordTestTrait.php
+++ b/tests/framework/ar/ActiveRecordTestTrait.php
@@ -8,6 +8,8 @@
 
 namespace yiiunit\framework\ar;
 
+use yiiunit\extensions\redis\ActiveRecordTest;
+use Exception;
 use yii\base\Event;
 use yii\db\ActiveRecordInterface;
 use yii\db\BaseActiveRecord;
@@ -62,7 +64,7 @@ trait ActiveRecordTestTrait
     {
     }
 
-    public function testFind()
+    public function testFind(): void
     {
         /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
@@ -125,7 +127,7 @@ trait ActiveRecordTestTrait
         $this->assertEquals(2, $customerClass::find()->active()->count());
     }
 
-    public function testFindAsArray()
+    public function testFindAsArray(): void
     {
         /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
@@ -161,7 +163,7 @@ trait ActiveRecordTestTrait
         $this->assertArrayHasKey('status', $customers[2]);
     }
 
-    public function testHasAttribute()
+    public function testHasAttribute(): void
     {
         /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
@@ -181,7 +183,7 @@ trait ActiveRecordTestTrait
         $this->assertFalse($customer->hasAttribute(42));
     }
 
-    public function testFindScalar()
+    public function testFindScalar(): void
     {
         /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
@@ -198,7 +200,7 @@ trait ActiveRecordTestTrait
         $this->assertEquals(3, $customerId);
     }
 
-    public function testFindColumn()
+    public function testFindColumn(): void
     {
         /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
@@ -208,7 +210,7 @@ trait ActiveRecordTestTrait
         $this->assertEquals(['user3', 'user2', 'user1'], $customerClass::find()->orderBy(['name' => SORT_DESC])->column('name'));
     }
 
-    public function testFindIndexBy()
+    public function testFindIndexBy(): void
     {
         /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
@@ -230,7 +232,7 @@ trait ActiveRecordTestTrait
         $this->assertInstanceOf($customerClass, $customers['3-user3']);
     }
 
-    public function testFindIndexByAsArray()
+    public function testFindIndexByAsArray(): void
     {
         /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
@@ -277,7 +279,7 @@ trait ActiveRecordTestTrait
         $this->assertArrayHasKey('status', $customers['3-user3']);
     }
 
-    public function testRefresh()
+    public function testRefresh(): void
     {
         /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
@@ -291,7 +293,7 @@ trait ActiveRecordTestTrait
         $this->assertEquals('user1', $customer->name);
     }
 
-    public function testEquals()
+    public function testEquals(): void
     {
         /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
@@ -319,7 +321,7 @@ trait ActiveRecordTestTrait
         $this->assertFalse($customerA->equals($customerB));
     }
 
-    public function testFindCount()
+    public function testFindCount(): void
     {
         /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
@@ -339,7 +341,7 @@ trait ActiveRecordTestTrait
         $this->assertEquals(3, $customerClass::find()->offset(2)->limit(2)->count());
     }
 
-    public function testFindLimit()
+    public function testFindLimit(): void
     {
         /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
@@ -386,7 +388,7 @@ trait ActiveRecordTestTrait
         $this->assertNull($customer);
     }
 
-    public function testFindComplexCondition()
+    public function testFindComplexCondition(): void
     {
         /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
@@ -402,7 +404,7 @@ trait ActiveRecordTestTrait
         $this->assertCount(1, $customerClass::find()->where(['AND', ['name' => ['user2', 'user3']], ['BETWEEN', 'status', 2, 4]])->all());
     }
 
-    public function testFindNullValues()
+    public function testFindNullValues(): void
     {
         /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
@@ -418,7 +420,7 @@ trait ActiveRecordTestTrait
         $this->assertEquals(2, reset($result)->primaryKey);
     }
 
-    public function testExists()
+    public function testExists(): void
     {
         /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
@@ -434,7 +436,7 @@ trait ActiveRecordTestTrait
         $this->assertFalse($customerClass::find()->where(['id' => [2, 3]])->offset(2)->exists());
     }
 
-    public function testFindLazy()
+    public function testFindLazy(): void
     {
         /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
@@ -462,7 +464,7 @@ trait ActiveRecordTestTrait
         $this->assertEquals(3, $orders[0]->id);
     }
 
-    public function testFindEager()
+    public function testFindEager(): void
     {
         /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
@@ -499,7 +501,7 @@ trait ActiveRecordTestTrait
         $this->assertTrue($orders[0]->isRelationPopulated('items'));
     }
 
-    public function testFindLazyVia()
+    public function testFindLazyVia(): void
     {
         /** @var ActiveRecordInterface $orderClass */
         $orderClass = $this->getOrderClass();
@@ -513,7 +515,7 @@ trait ActiveRecordTestTrait
         $this->assertEquals(2, $order->items[1]->id);
     }
 
-    public function testFindLazyVia2()
+    public function testFindLazyVia2(): void
     {
         /** @var ActiveRecordInterface $orderClass */
         $orderClass = $this->getOrderClass();
@@ -525,7 +527,7 @@ trait ActiveRecordTestTrait
         $this->assertEquals([], $order->items);
     }
 
-    public function testFindEagerViaRelation()
+    public function testFindEagerViaRelation(): void
     {
         /** @var ActiveRecordInterface $orderClass */
         $orderClass = $this->getOrderClass();
@@ -541,7 +543,7 @@ trait ActiveRecordTestTrait
         $this->assertEquals(2, $order->items[1]->id);
     }
 
-    public function testFindNestedRelation()
+    public function testFindNestedRelation(): void
     {
         /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
@@ -578,7 +580,7 @@ trait ActiveRecordTestTrait
      *
      * @see https://github.com/yiisoft/yii2/issues/1310.
      */
-    public function testFindEagerViaRelationPreserveOrder()
+    public function testFindEagerViaRelationPreserveOrder(): void
     {
         /** @var ActiveRecordInterface $orderClass */
         $orderClass = $this->getOrderClass();
@@ -641,7 +643,7 @@ trait ActiveRecordTestTrait
     }
 
     // different order in via table
-    public function testFindEagerViaRelationPreserveOrderB()
+    public function testFindEagerViaRelationPreserveOrderB(): void
     {
         /** @var ActiveRecordInterface $orderClass */
         $orderClass = $this->getOrderClass();
@@ -671,7 +673,7 @@ trait ActiveRecordTestTrait
         $this->assertEquals(2, $order->itemsInOrder2[0]->id);
     }
 
-    public function testLink()
+    public function testLink(): void
     {
         /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
@@ -724,7 +726,7 @@ trait ActiveRecordTestTrait
         $this->assertEquals(100, $orderItem->subtotal);
     }
 
-    public function testUnlink()
+    public function testUnlink(): void
     {
         /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
@@ -775,7 +777,7 @@ trait ActiveRecordTestTrait
         $this->assertCount(2, $order->orderItems);
     }
 
-    public function testUnlinkAll()
+    public function testUnlinkAll(): void
     {
         /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
@@ -841,7 +843,7 @@ trait ActiveRecordTestTrait
         // via table is covered in \yiiunit\framework\db\ActiveRecordTest::testUnlinkAllViaTable()
     }
 
-    public function testUnlinkAllAndConditionSetNull()
+    public function testUnlinkAllAndConditionSetNull(): void
     {
         /** @var TestCase|ActiveRecordTestTrait $this */
 
@@ -867,7 +869,7 @@ trait ActiveRecordTestTrait
         $this->assertCount(0, $customer->expensiveOrdersWithNullFK);
     }
 
-    public function testUnlinkAllAndConditionDelete()
+    public function testUnlinkAllAndConditionDelete(): void
     {
         /** @var TestCase|ActiveRecordTestTrait $this */
 
@@ -896,7 +898,7 @@ trait ActiveRecordTestTrait
     public static $afterSaveNewRecord;
     public static $afterSaveInsert;
 
-    public function testInsert()
+    public function testInsert(): void
     {
         /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
@@ -920,7 +922,7 @@ trait ActiveRecordTestTrait
         $this->assertFalse($customer->isNewRecord);
     }
 
-    public function testExplicitPkOnAutoIncrement()
+    public function testExplicitPkOnAutoIncrement(): void
     {
         /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
@@ -939,7 +941,7 @@ trait ActiveRecordTestTrait
         $this->assertFalse($customer->isNewRecord);
     }
 
-    public function testUpdate()
+    public function testUpdate(): void
     {
         /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
@@ -982,7 +984,7 @@ trait ActiveRecordTestTrait
         $this->assertEquals(0, $ret);
     }
 
-    public function testUpdateAttributes()
+    public function testUpdateAttributes(): void
     {
         /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
@@ -1017,7 +1019,7 @@ trait ActiveRecordTestTrait
         $this->assertEquals(1, $customer->status);
     }
 
-    public function testUpdateCounters()
+    public function testUpdateCounters(): void
     {
         /** @var ActiveRecordInterface $orderItemClass */
         $orderItemClass = $this->getOrderItemClass();
@@ -1048,7 +1050,7 @@ trait ActiveRecordTestTrait
         $this->assertEquals(30, $orderItem->subtotal);
     }
 
-    public function testDelete()
+    public function testDelete(): void
     {
         /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
@@ -1080,7 +1082,7 @@ trait ActiveRecordTestTrait
      * Some PDO implementations(e.g. cubrid) do not support boolean values.
      * Make sure this does not affect AR layer.
      */
-    public function testBooleanAttribute()
+    public function testBooleanAttribute(): void
     {
         /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
@@ -1107,7 +1109,7 @@ trait ActiveRecordTestTrait
         $this->assertCount(1, $customers);
     }
 
-    public function testAfterFind()
+    public function testAfterFind(): void
     {
         /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
@@ -1145,7 +1147,7 @@ trait ActiveRecordTestTrait
         ], $afterFindCalls);
         $afterFindCalls = [];
 
-        if ($this instanceof \yiiunit\extensions\redis\ActiveRecordTest) { // TODO redis does not support orderBy() yet
+        if ($this instanceof ActiveRecordTest) { // TODO redis does not support orderBy() yet
             $customer = $customerClass::find()->where(['id' => [1, 2]])->with('orders')->all();
         } else {
             // orderBy is needed to avoid random test failure
@@ -1164,7 +1166,7 @@ trait ActiveRecordTestTrait
         Event::off(BaseActiveRecord::className(), BaseActiveRecord::EVENT_AFTER_FIND);
     }
 
-    public function testAfterRefresh()
+    public function testAfterRefresh(): void
     {
         /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
@@ -1185,7 +1187,7 @@ trait ActiveRecordTestTrait
         Event::off(BaseActiveRecord::className(), BaseActiveRecord::EVENT_AFTER_REFRESH);
     }
 
-    public function testFindEmptyInCondition()
+    public function testFindEmptyInCondition(): void
     {
         /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
@@ -1204,7 +1206,7 @@ trait ActiveRecordTestTrait
         $this->assertCount(0, $customers);
     }
 
-    public function testFindEagerIndexBy()
+    public function testFindEagerIndexBy(): void
     {
         /** @var TestCase|ActiveRecordTestTrait $this */
 
@@ -1229,7 +1231,7 @@ trait ActiveRecordTestTrait
         $this->assertTrue(isset($items[5]));
     }
 
-    public function testAttributeAccess()
+    public function testAttributeAccess(): void
     {
         /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
@@ -1278,7 +1280,7 @@ trait ActiveRecordTestTrait
             $itemClass = $this->getItemClass();
             $customer->orderItems = [new $itemClass()];
             $this->fail('setter call above MUST throw Exception');
-        } catch (\Exception $e) {
+        } catch (Exception $e) {
             // catch exception "Setting read-only property"
             $this->assertInstanceOf('yii\base\InvalidCallException', $e);
         }
@@ -1293,7 +1295,7 @@ trait ActiveRecordTestTrait
     /**
      * @see https://github.com/yiisoft/yii2/issues/17089
      */
-    public function testViaWithCallable()
+    public function testViaWithCallable(): void
     {
         /** @var ActiveRecordInterface $orderClass */
         $orderClass = $this->getOrderClass();
diff --git a/tests/framework/behaviors/SluggableBehaviorTest.php b/tests/framework/behaviors/SluggableBehaviorTest.php
index 2882cae734..ee825672ff 100644
--- a/tests/framework/behaviors/SluggableBehaviorTest.php
+++ b/tests/framework/behaviors/SluggableBehaviorTest.php
@@ -71,7 +71,7 @@ class SluggableBehaviorTest extends TestCase
 
     // Tests :
 
-    public function testSlug()
+    public function testSlug(): void
     {
         $model = new ActiveRecordSluggable();
         $model->name = 'test name';
@@ -83,7 +83,7 @@ class SluggableBehaviorTest extends TestCase
     /**
      * @depends testSlug
      */
-    public function testSlugSeveralAttributes()
+    public function testSlugSeveralAttributes(): void
     {
         $model = new ActiveRecordSluggable();
         $model->getBehavior('sluggable')->attribute = ['name', 'category_id'];
@@ -98,7 +98,7 @@ class SluggableBehaviorTest extends TestCase
     /**
      * @depends testSlug
      */
-    public function testSlugRelatedAttribute()
+    public function testSlugRelatedAttribute(): void
     {
         $model = new ActiveRecordSluggable();
         $model->getBehavior('sluggable')->attribute = 'related.name';
@@ -117,7 +117,7 @@ class SluggableBehaviorTest extends TestCase
     /**
      * @depends testSlug
      */
-    public function testUniqueByIncrement()
+    public function testUniqueByIncrement(): void
     {
         $name = 'test name';
 
@@ -136,7 +136,7 @@ class SluggableBehaviorTest extends TestCase
     /**
      * @depends testUniqueByIncrement
      */
-    public function testUniqueByCallback()
+    public function testUniqueByCallback(): void
     {
         $name = 'test name';
 
@@ -157,7 +157,7 @@ class SluggableBehaviorTest extends TestCase
     /**
      * @depends testSlug
      */
-    public function testUpdateUnique()
+    public function testUpdateUnique(): void
     {
         $name = 'test name';
 
@@ -177,7 +177,7 @@ class SluggableBehaviorTest extends TestCase
         $this->assertEquals('test-name', $model->slug);
     }
 
-    public function testSkipOnEmpty()
+    public function testSkipOnEmpty(): void
     {
         $model = new SkipOnEmptySluggableActiveRecord();
         $model->name = 'test name';
@@ -196,7 +196,7 @@ class SluggableBehaviorTest extends TestCase
     /**
      * @depends testSlug
      */
-    public function testImmutableByAttribute()
+    public function testImmutableByAttribute(): void
     {
         $model = new ActiveRecordSluggable();
         $model->getSluggable()->immutable = true;
@@ -213,7 +213,7 @@ class SluggableBehaviorTest extends TestCase
     /**
      * @depends testSlug
      */
-    public function testImmutableByCallback()
+    public function testImmutableByCallback(): void
     {
         $model = new ActiveRecordSluggable();
         $model->getSluggable()->immutable = true;
diff --git a/tests/framework/behaviors/TimestampBehaviorTest.php b/tests/framework/behaviors/TimestampBehaviorTest.php
index cf97023ded..1799a4c9a7 100644
--- a/tests/framework/behaviors/TimestampBehaviorTest.php
+++ b/tests/framework/behaviors/TimestampBehaviorTest.php
@@ -72,7 +72,7 @@ class TimestampBehaviorTest extends TestCase
 
     // Tests :
 
-    public function testNewRecord()
+    public function testNewRecord(): void
     {
         $currentTime = time();
 
@@ -89,7 +89,7 @@ class TimestampBehaviorTest extends TestCase
     /**
      * @depends testNewRecord
      */
-    public function testUpdateRecord()
+    public function testUpdateRecord(): void
     {
         $currentTime = time();
 
@@ -112,7 +112,7 @@ class TimestampBehaviorTest extends TestCase
     /**
      * @depends testNewRecord
      */
-    public function testUpdateCleanRecord()
+    public function testUpdateCleanRecord(): void
     {
         ActiveRecordTimestamp::$behaviors = [
             TimestampBehavior::className(),
@@ -151,7 +151,7 @@ class TimestampBehaviorTest extends TestCase
      * @param mixed $expression
      * @param mixed $expected
      */
-    public function testNewRecordExpression($expression, $expected)
+    public function testNewRecordExpression($expression, $expected): void
     {
         ActiveRecordTimestamp::$tableName = 'test_auto_timestamp_string';
         ActiveRecordTimestamp::$behaviors = [
@@ -179,7 +179,7 @@ class TimestampBehaviorTest extends TestCase
     /**
      * @depends testNewRecord
      */
-    public function testUpdateRecordExpression()
+    public function testUpdateRecordExpression(): void
     {
         ActiveRecordTimestamp::$tableName = 'test_auto_timestamp_string';
         ActiveRecordTimestamp::$behaviors = [
@@ -203,7 +203,7 @@ class TimestampBehaviorTest extends TestCase
         $this->assertEquals(date('Y'), $model->updated_at);
     }
 
-    public function testTouchingNewRecordGeneratesException()
+    public function testTouchingNewRecordGeneratesException(): void
     {
         ActiveRecordTimestamp::$behaviors = [
             'timestamp' => [
@@ -218,7 +218,7 @@ class TimestampBehaviorTest extends TestCase
         $model->touch('created_at');
     }
 
-    public function testTouchingNotNewRecord()
+    public function testTouchingNotNewRecord(): void
     {
         ActiveRecordTimestamp::$behaviors = [
             'timestamp' => [
diff --git a/tests/framework/caching/ApcCacheTest.php b/tests/framework/caching/ApcCacheTest.php
index 83d57d893a..42e06bab98 100644
--- a/tests/framework/caching/ApcCacheTest.php
+++ b/tests/framework/caching/ApcCacheTest.php
@@ -43,12 +43,12 @@ class ApcCacheTest extends CacheTestCase
         return $this->_cacheInstance;
     }
 
-    public function testExpire()
+    public function testExpire(): void
     {
         $this->markTestSkipped('APC keys are expiring only on the next request.');
     }
 
-    public function testExpireAdd()
+    public function testExpireAdd(): void
     {
         $this->markTestSkipped('APC keys are expiring only on the next request.');
     }
diff --git a/tests/framework/caching/ArrayCacheTest.php b/tests/framework/caching/ArrayCacheTest.php
index ba4249a049..87b23ec2a9 100644
--- a/tests/framework/caching/ArrayCacheTest.php
+++ b/tests/framework/caching/ArrayCacheTest.php
@@ -30,7 +30,7 @@ class ArrayCacheTest extends CacheTestCase
         return $this->_cacheInstance;
     }
 
-    public function testExpire()
+    public function testExpire(): void
     {
         $cache = $this->getCacheInstance();
 
@@ -42,7 +42,7 @@ class ArrayCacheTest extends CacheTestCase
         $this->assertFalse($cache->get('expire_test'));
     }
 
-    public function testExpireAdd()
+    public function testExpireAdd(): void
     {
         $cache = $this->getCacheInstance();
 
@@ -57,7 +57,7 @@ class ArrayCacheTest extends CacheTestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/16028
      */
-    public function testSerializationOfComplexKeysThatContainNonUTFSequences()
+    public function testSerializationOfComplexKeysThatContainNonUTFSequences(): void
     {
         $cache = $this->getCacheInstance();
 
diff --git a/tests/framework/caching/CacheTestCase.php b/tests/framework/caching/CacheTestCase.php
index 1fce0a44fa..8147daa912 100644
--- a/tests/framework/caching/CacheTestCase.php
+++ b/tests/framework/caching/CacheTestCase.php
@@ -82,7 +82,7 @@ abstract class CacheTestCase extends TestCase
         return $cache;
     }
 
-    public function testSet()
+    public function testSet(): void
     {
         $cache = $this->getCacheInstance();
 
@@ -91,7 +91,7 @@ abstract class CacheTestCase extends TestCase
         $this->assertTrue($cache->set('array_test', ['array_test' => 'array_test']));
     }
 
-    public function testGet()
+    public function testGet(): void
     {
         $cache = $this->prepare();
 
@@ -116,7 +116,7 @@ abstract class CacheTestCase extends TestCase
      * @dataProvider multiSetExpiry
      * @param int $expiry
      */
-    public function testMultiset($expiry)
+    public function testMultiset($expiry): void
     {
         $cache = $this->getCacheInstance();
         $cache->flush();
@@ -136,7 +136,7 @@ abstract class CacheTestCase extends TestCase
         $this->assertEquals('array_test', $array['array_test']);
     }
 
-    public function testExists()
+    public function testExists(): void
     {
         $cache = $this->prepare();
 
@@ -148,7 +148,7 @@ abstract class CacheTestCase extends TestCase
         $this->assertFalse($cache->exists('not_exists'));
     }
 
-    public function testArrayAccess()
+    public function testArrayAccess(): void
     {
         $cache = $this->getCacheInstance();
 
@@ -156,21 +156,21 @@ abstract class CacheTestCase extends TestCase
         $this->assertInstanceOf('stdClass', $cache['arrayaccess_test']);
     }
 
-    public function testGetValueNonExistent()
+    public function testGetValueNonExistent(): void
     {
         $cache = $this->getCacheInstance();
 
         $this->assertFalse($this->invokeMethod($cache, 'getValue', ['non_existent_key']));
     }
 
-    public function testGetNonExistent()
+    public function testGetNonExistent(): void
     {
         $cache = $this->getCacheInstance();
 
         $this->assertFalse($cache->get('non_existent_key'));
     }
 
-    public function testStoreSpecialValues()
+    public function testStoreSpecialValues(): void
     {
         $cache = $this->getCacheInstance();
 
@@ -181,7 +181,7 @@ abstract class CacheTestCase extends TestCase
         $this->assertTrue($cache->get('bool_value'));
     }
 
-    public function testMultiGet()
+    public function testMultiGet(): void
     {
         $cache = $this->prepare();
 
@@ -191,14 +191,14 @@ abstract class CacheTestCase extends TestCase
         $this->assertSame(['number_test' => 42, 'non_existent_key' => false], $cache->multiGet(['number_test', 'non_existent_key']));
     }
 
-    public function testDefaultTtl()
+    public function testDefaultTtl(): void
     {
         $cache = $this->getCacheInstance();
 
         $this->assertSame(0, $cache->defaultDuration);
     }
 
-    public function testExpire()
+    public function testExpire(): void
     {
         $cache = $this->getCacheInstance();
 
@@ -209,7 +209,7 @@ abstract class CacheTestCase extends TestCase
         $this->assertFalse($cache->get('expire_test'));
     }
 
-    public function testExpireAdd()
+    public function testExpireAdd(): void
     {
         $cache = $this->getCacheInstance();
 
@@ -220,7 +220,7 @@ abstract class CacheTestCase extends TestCase
         $this->assertFalse($cache->get('expire_testa'));
     }
 
-    public function testAdd()
+    public function testAdd(): void
     {
         $cache = $this->prepare();
 
@@ -234,7 +234,7 @@ abstract class CacheTestCase extends TestCase
         $this->assertEquals(13, $cache->get('add_test'));
     }
 
-    public function testMultiAdd()
+    public function testMultiAdd(): void
     {
         $cache = $this->prepare();
 
@@ -249,7 +249,7 @@ abstract class CacheTestCase extends TestCase
         $this->assertEquals(13, $cache->get('add_test'));
     }
 
-    public function testDelete()
+    public function testDelete(): void
     {
         $cache = $this->prepare();
 
@@ -258,14 +258,14 @@ abstract class CacheTestCase extends TestCase
         $this->assertFalse($cache->get('number_test'));
     }
 
-    public function testFlush()
+    public function testFlush(): void
     {
         $cache = $this->prepare();
         $this->assertTrue($cache->flush());
         $this->assertFalse($cache->get('number_test'));
     }
 
-    public function testGetOrSet()
+    public function testGetOrSet(): void
     {
         $cache = $this->prepare();
 
@@ -282,7 +282,7 @@ abstract class CacheTestCase extends TestCase
         return get_class($cache);
     }
 
-    public function testGetOrSetWithDependencies()
+    public function testGetOrSetWithDependencies(): void
     {
         $cache = $this->prepare();
         $dependency = new TagDependency(['tags' => 'test']);
diff --git a/tests/framework/caching/CallbackDependencyTest.php b/tests/framework/caching/CallbackDependencyTest.php
index b2a93ff954..ac284068f2 100644
--- a/tests/framework/caching/CallbackDependencyTest.php
+++ b/tests/framework/caching/CallbackDependencyTest.php
@@ -8,7 +8,7 @@ use yii\caching\CallbackDependency;
 
 class CallbackDependencyTest extends TestCase
 {
-    public function testDependencyChange()
+    public function testDependencyChange(): void
     {
         $cache = new ArrayCache();
         $dependencyValue = true;
@@ -25,7 +25,7 @@ class CallbackDependencyTest extends TestCase
         $this->assertTrue($dependency->isChanged($cache));
     }
 
-    public function testDependencyNotChanged()
+    public function testDependencyNotChanged(): void
     {
         $cache = new ArrayCache();
 
diff --git a/tests/framework/caching/DbCacheTest.php b/tests/framework/caching/DbCacheTest.php
index e05aa446aa..4f43db38d0 100644
--- a/tests/framework/caching/DbCacheTest.php
+++ b/tests/framework/caching/DbCacheTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\caching;
 
+use yii\db\Connection;
 use yii\caching\DbCache;
 
 /**
@@ -41,14 +42,14 @@ class DbCacheTest extends CacheTestCase
 
     /**
      * @param  bool            $reset whether to clean up the test database
-     * @return \yii\db\Connection
+     * @return Connection
      */
     public function getConnection($reset = true)
     {
         if ($this->_connection === null) {
             $databases = self::getParam('databases');
             $params = $databases['mysql'];
-            $db = new \yii\db\Connection();
+            $db = new Connection();
             $db->dsn = $params['dsn'];
             $db->username = $params['username'];
             $db->password = $params['password'];
@@ -79,7 +80,7 @@ class DbCacheTest extends CacheTestCase
         return $this->_cacheInstance;
     }
 
-    public function testExpire()
+    public function testExpire(): void
     {
         $cache = $this->getCacheInstance();
 
@@ -91,7 +92,7 @@ class DbCacheTest extends CacheTestCase
         $this->assertFalse($cache->get('expire_test'));
     }
 
-    public function testExpireAdd()
+    public function testExpireAdd(): void
     {
         $cache = $this->getCacheInstance();
 
@@ -103,7 +104,7 @@ class DbCacheTest extends CacheTestCase
         $this->assertFalse($cache->get('expire_testa'));
     }
 
-    public function testSynchronousSetWithTheSameKey()
+    public function testSynchronousSetWithTheSameKey(): void
     {
         $KEY = 'sync-test-key';
         $VALUE = 'sync-test-value';
diff --git a/tests/framework/caching/DbDependencyTest.php b/tests/framework/caching/DbDependencyTest.php
index be7e002cce..48a8a6a84a 100644
--- a/tests/framework/caching/DbDependencyTest.php
+++ b/tests/framework/caching/DbDependencyTest.php
@@ -39,7 +39,7 @@ class DbDependencyTest extends DatabaseTestCase
         $db->createCommand()->insert('dependency_item', ['value' => 'initial'])->execute();
     }
 
-    public function testQueryOneIsExecutedWhenQueryCacheEnabled()
+    public function testQueryOneIsExecutedWhenQueryCacheEnabled(): void
     {
         $db = $this->getConnection(false);
         $cache = new ArrayCache();
@@ -60,7 +60,7 @@ class DbDependencyTest extends DatabaseTestCase
         $this->assertTrue($dependency->isChanged($cache));
     }
 
-    public function testQueryOneIsExecutedWhenQueryCacheDisabled()
+    public function testQueryOneIsExecutedWhenQueryCacheDisabled(): void
     {
         $db = $this->getConnection(false);
         $cache = new ArrayCache();
@@ -81,7 +81,7 @@ class DbDependencyTest extends DatabaseTestCase
         $this->assertTrue($dependency->isChanged($cache));
     }
 
-    public function testMissingSqlThrowsException()
+    public function testMissingSqlThrowsException(): void
     {
         $this->expectException('\yii\base\InvalidConfigException');
 
diff --git a/tests/framework/caching/DbQueryDependencyTest.php b/tests/framework/caching/DbQueryDependencyTest.php
index e7ac7fd24a..e8e01d2850 100644
--- a/tests/framework/caching/DbQueryDependencyTest.php
+++ b/tests/framework/caching/DbQueryDependencyTest.php
@@ -37,7 +37,7 @@ class DbQueryDependencyTest extends DatabaseTestCase
         $db->createCommand()->insert('dependency_item', ['value' => 'initial'])->execute();
     }
 
-    public function testIsChanged()
+    public function testIsChanged(): void
     {
         $db = $this->getConnection(false);
         $cache = new ArrayCache();
@@ -62,7 +62,7 @@ class DbQueryDependencyTest extends DatabaseTestCase
     /**
      * @depends testIsChanged
      */
-    public function testCustomMethod()
+    public function testCustomMethod(): void
     {
         $db = $this->getConnection(false);
         $cache = new ArrayCache();
@@ -86,7 +86,7 @@ class DbQueryDependencyTest extends DatabaseTestCase
     /**
      * @depends testCustomMethod
      */
-    public function testCustomMethodCallback()
+    public function testCustomMethodCallback(): void
     {
         $db = $this->getConnection(false);
         $cache = new ArrayCache();
@@ -112,7 +112,7 @@ class DbQueryDependencyTest extends DatabaseTestCase
     /**
      * @depends testCustomMethod
      */
-    public function testReusableAndCustomMethodCallback()
+    public function testReusableAndCustomMethodCallback(): void
     {
         $db = $this->getConnection(false);
         $cache = new ArrayCache();
diff --git a/tests/framework/caching/DependencyTest.php b/tests/framework/caching/DependencyTest.php
index 05010e1058..1eb3aeb24b 100644
--- a/tests/framework/caching/DependencyTest.php
+++ b/tests/framework/caching/DependencyTest.php
@@ -21,7 +21,7 @@ use yiiunit\TestCase;
  */
 class DependencyTest extends TestCase
 {
-    public function testResetReusableData()
+    public function testResetReusableData(): void
     {
         $value = ['dummy'];
         $dependency = new MockDependency();
@@ -33,7 +33,7 @@ class DependencyTest extends TestCase
         $this->assertEquals([], $this->getInaccessibleProperty($dependency, '_reusableData'));
     }
 
-    public function testGenerateReusableHash()
+    public function testGenerateReusableHash(): void
     {
         $dependency = $this->getMockForAbstractClass(Dependency::className());
         $dependency->data = 'dummy';
@@ -43,7 +43,7 @@ class DependencyTest extends TestCase
         $this->assertEquals(40, strlen($result));
     }
 
-    public function testIsChanged()
+    public function testIsChanged(): void
     {
         $dependency = $this->getMockForAbstractClass(Dependency::className());
         $cache = $this->getMockForAbstractClass(Cache::className());
diff --git a/tests/framework/caching/FileCacheTest.php b/tests/framework/caching/FileCacheTest.php
index 1f6f8747a1..85f69afb36 100644
--- a/tests/framework/caching/FileCacheTest.php
+++ b/tests/framework/caching/FileCacheTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\caching;
 
+use ReflectionClass;
 use yii\caching\FileCache;
 
 /**
@@ -30,7 +31,7 @@ class FileCacheTest extends CacheTestCase
         return $this->_cacheInstance;
     }
 
-    public function testExpire()
+    public function testExpire(): void
     {
         $cache = $this->getCacheInstance();
 
@@ -42,7 +43,7 @@ class FileCacheTest extends CacheTestCase
         $this->assertFalse($cache->get('expire_test'));
     }
 
-    public function testExpireAdd()
+    public function testExpireAdd(): void
     {
         $cache = $this->getCacheInstance();
 
@@ -54,7 +55,7 @@ class FileCacheTest extends CacheTestCase
         $this->assertFalse($cache->get('expire_testa'));
     }
 
-    public function testKeyPrefix()
+    public function testKeyPrefix(): void
     {
         $keyPrefix = 'foobar';
         $key = uniqid('uid-cache_');
@@ -68,7 +69,7 @@ class FileCacheTest extends CacheTestCase
 
         $value = \time();
 
-        $refClass = new \ReflectionClass($cache);
+        $refClass = new ReflectionClass($cache);
 
         $refMethodGetCacheFile = $refClass->getMethod('getCacheFile');
 
@@ -90,13 +91,13 @@ class FileCacheTest extends CacheTestCase
         $this->assertEquals($value, $refMethodGet->invoke($cache, $key));
     }
 
-    public function testStatCache()
+    public function testStatCache(): void
     {
         $cache = $this->getCacheInstance();
         $cache->set(__FUNCTION__, 'cache1', 2);
 
         $normalizeKey = $cache->buildKey(__FUNCTION__);
-        $refClass = new \ReflectionClass($cache);
+        $refClass = new ReflectionClass($cache);
         $refMethodGetCacheFile = $refClass->getMethod('getCacheFile');
 
         // @link https://wiki.php.net/rfc/deprecations_php_8_5#deprecate_reflectionsetaccessible
diff --git a/tests/framework/caching/MemCacheTest.php b/tests/framework/caching/MemCacheTest.php
index 61f2cac9dd..02644a08ab 100644
--- a/tests/framework/caching/MemCacheTest.php
+++ b/tests/framework/caching/MemCacheTest.php
@@ -40,7 +40,7 @@ class MemCacheTest extends CacheTestCase
         return $this->_cacheInstance;
     }
 
-    public function testExpire()
+    public function testExpire(): void
     {
         if (getenv('GITHUB_ACTIONS') == 'true') {
             $this->markTestSkipped('Can not reliably test memcache expiry on GitHub actions.');
@@ -48,7 +48,7 @@ class MemCacheTest extends CacheTestCase
         parent::testExpire();
     }
 
-    public function testExpireAdd()
+    public function testExpireAdd(): void
     {
         if (getenv('GITHUB_ACTIONS') == 'true') {
             $this->markTestSkipped('Can not reliably test memcache expiry on GitHub actions.');
diff --git a/tests/framework/caching/MemCachedTest.php b/tests/framework/caching/MemCachedTest.php
index 70c0668d21..d05e149d03 100644
--- a/tests/framework/caching/MemCachedTest.php
+++ b/tests/framework/caching/MemCachedTest.php
@@ -48,7 +48,7 @@ class MemCachedTest extends CacheTestCase
         return $this->_cacheInstance;
     }
 
-    public function testExpire()
+    public function testExpire(): void
     {
         if (getenv('GITHUB_ACTIONS') == 'true') {
             $this->markTestSkipped('Can not reliably test memcached expiry on GitHub actions.');
@@ -56,7 +56,7 @@ class MemCachedTest extends CacheTestCase
         parent::testExpire();
     }
 
-    public function testExpireAdd()
+    public function testExpireAdd(): void
     {
         if (getenv('GITHUB_ACTIONS') == 'true') {
             $this->markTestSkipped('Can not reliably test memcached expiry on GitHub actions.');
diff --git a/tests/framework/caching/MssqlCacheTest.php b/tests/framework/caching/MssqlCacheTest.php
index 42f5b105bf..fc64010715 100644
--- a/tests/framework/caching/MssqlCacheTest.php
+++ b/tests/framework/caching/MssqlCacheTest.php
@@ -42,7 +42,7 @@ class MssqlCacheTest extends CacheTestCase
 
     /**
      * @param  bool            $reset whether to clean up the test database
-     * @return \yii\db\Connection
+     * @return Connection
      */
     public function getConnection($reset = true)
     {
@@ -79,7 +79,7 @@ class MssqlCacheTest extends CacheTestCase
         return $this->_cacheInstance;
     }
 
-    public function testExpire()
+    public function testExpire(): void
     {
         $cache = $this->getCacheInstance();
 
@@ -91,7 +91,7 @@ class MssqlCacheTest extends CacheTestCase
         $this->assertFalse($cache->get('expire_test'));
     }
 
-    public function testExpireAdd()
+    public function testExpireAdd(): void
     {
         $cache = $this->getCacheInstance();
 
@@ -103,7 +103,7 @@ class MssqlCacheTest extends CacheTestCase
         $this->assertFalse($cache->get('expire_testa'));
     }
 
-    public function testSynchronousSetWithTheSameKey()
+    public function testSynchronousSetWithTheSameKey(): void
     {
         $KEY = 'sync-test-key';
         $VALUE = 'sync-test-value';
diff --git a/tests/framework/caching/TagDependencyTest.php b/tests/framework/caching/TagDependencyTest.php
index 41f9552dd0..e7fdea3469 100644
--- a/tests/framework/caching/TagDependencyTest.php
+++ b/tests/framework/caching/TagDependencyTest.php
@@ -17,7 +17,7 @@ use yiiunit\TestCase;
  */
 class TagDependencyTest extends TestCase
 {
-    public function testInvalidate()
+    public function testInvalidate(): void
     {
         $cache = new FileCache(['cachePath' => '@yiiunit/runtime/cache']);
 
diff --git a/tests/framework/console/ControllerTest.php b/tests/framework/console/ControllerTest.php
index 6922baa9a4..9ed3a7868d 100644
--- a/tests/framework/console/ControllerTest.php
+++ b/tests/framework/console/ControllerTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\console;
 
+use yii\data\ArrayDataProvider;
 use RuntimeException;
 use yii\console\Exception;
 use yiiunit\framework\console\stubs\DummyService;
@@ -38,7 +39,7 @@ class ControllerTest extends TestCase
         ];
     }
 
-    public function testBindArrayToActionParams()
+    public function testBindArrayToActionParams(): void
     {
         $controller = new FakeController('fake', Yii::$app);
 
@@ -47,7 +48,7 @@ class ControllerTest extends TestCase
         $this->assertEquals([], $controller->runAction('aksi4', $params));
     }
 
-    public function testBindActionParams()
+    public function testBindActionParams(): void
     {
         $controller = new FakeController('fake', Yii::$app);
 
@@ -105,7 +106,7 @@ class ControllerTest extends TestCase
         $result = $controller->runAction('aksi3', $params);
     }
 
-    public function testNullableInjectedActionParams()
+    public function testNullableInjectedActionParams(): void
     {
         // Use the PHP71 controller for this test
         $this->controller = new FakePhp71Controller('fake', new Application([
@@ -117,11 +118,11 @@ class ControllerTest extends TestCase
         $injectionAction = new InlineAction('injection', $this->controller, 'actionNullableInjection');
         $params = [];
         $args = $this->controller->bindActionParams($injectionAction, $params);
-        $this->assertEquals(\Yii::$app->request, $args[0]);
+        $this->assertEquals(Yii::$app->request, $args[0]);
         $this->assertNull($args[1]);
     }
 
-    public function testInjectionContainerException()
+    public function testInjectionContainerException(): void
     {
         // Use the PHP71 controller for this test
         $this->controller = new FakePhp71Controller('fake', new Application([
@@ -132,8 +133,8 @@ class ControllerTest extends TestCase
 
         $injectionAction = new InlineAction('injection', $this->controller, 'actionInjection');
         $params = ['between' => 'test', 'after' => 'another', 'before' => 'test'];
-        \Yii::$container->set(DummyService::className(), function () {
-            throw new \RuntimeException('uh oh');
+        Yii::$container->set(DummyService::className(), function () {
+            throw new RuntimeException('uh oh');
         });
 
         $this->expectException(get_class(new RuntimeException()));
@@ -141,7 +142,7 @@ class ControllerTest extends TestCase
         $this->controller->bindActionParams($injectionAction, $params);
     }
 
-    public function testUnknownInjection()
+    public function testUnknownInjection(): void
     {
         // Use the PHP71 controller for this test
         $this->controller = new FakePhp71Controller('fake', new Application([
@@ -152,13 +153,13 @@ class ControllerTest extends TestCase
 
         $injectionAction = new InlineAction('injection', $this->controller, 'actionInjection');
         $params = ['between' => 'test', 'after' => 'another', 'before' => 'test'];
-        \Yii::$container->clear(DummyService::className());
+        Yii::$container->clear(DummyService::className());
         $this->expectException(get_class(new Exception()));
         $this->expectExceptionMessage('Could not load required service: dummyService');
         $this->controller->bindActionParams($injectionAction, $params);
     }
 
-    public function testInjectedActionParams()
+    public function testInjectedActionParams(): void
     {
         // Use the PHP71 controller for this test
         $this->controller = new FakePhp71Controller('fake', new Application([
@@ -169,27 +170,27 @@ class ControllerTest extends TestCase
 
         $injectionAction = new InlineAction('injection', $this->controller, 'actionInjection');
         $params = ['between' => 'test', 'after' => 'another', 'before' => 'test'];
-        \Yii::$container->set(DummyService::className(), DummyService::className());
+        Yii::$container->set(DummyService::className(), DummyService::className());
         $args = $this->controller->bindActionParams($injectionAction, $params);
         $this->assertEquals($params['before'], $args[0]);
-        $this->assertEquals(\Yii::$app->request, $args[1]);
-        $this->assertEquals('Component: yii\console\Request $request', \Yii::$app->requestedParams['request']);
+        $this->assertEquals(Yii::$app->request, $args[1]);
+        $this->assertEquals('Component: yii\console\Request $request', Yii::$app->requestedParams['request']);
         $this->assertEquals($params['between'], $args[2]);
         $this->assertInstanceOf(DummyService::className(), $args[3]);
-        $this->assertEquals('Container DI: yiiunit\framework\console\stubs\DummyService $dummyService', \Yii::$app->requestedParams['dummyService']);
+        $this->assertEquals('Container DI: yiiunit\framework\console\stubs\DummyService $dummyService', Yii::$app->requestedParams['dummyService']);
         $this->assertNull($args[4]);
-        $this->assertEquals('Unavailable service: post', \Yii::$app->requestedParams['post']);
+        $this->assertEquals('Unavailable service: post', Yii::$app->requestedParams['post']);
         $this->assertEquals($params['after'], $args[5]);
     }
 
-    public function testInjectedActionParamsFromModule()
+    public function testInjectedActionParamsFromModule(): void
     {
-        $module = new \yii\base\Module('fake', new Application([
+        $module = new Module('fake', new Application([
             'id' => 'app',
             'basePath' => __DIR__,
         ]));
         $module->set('yii\data\DataProviderInterface', [
-            'class' => \yii\data\ArrayDataProvider::className(),
+            'class' => ArrayDataProvider::className(),
         ]);
         // Use the PHP71 controller for this test
         $this->controller = new FakePhp71Controller('fake', $module);
@@ -197,11 +198,11 @@ class ControllerTest extends TestCase
 
         $injectionAction = new InlineAction('injection', $this->controller, 'actionModuleServiceInjection');
         $args = $this->controller->bindActionParams($injectionAction, []);
-        $this->assertInstanceOf(\yii\data\ArrayDataProvider::className(), $args[0]);
-        $this->assertEquals('Module yii\base\Module DI: yii\data\DataProviderInterface $dataProvider', \Yii::$app->requestedParams['dataProvider']);
+        $this->assertInstanceOf(ArrayDataProvider::className(), $args[0]);
+        $this->assertEquals('Module yii\base\Module DI: yii\data\DataProviderInterface $dataProvider', Yii::$app->requestedParams['dataProvider']);
     }
 
-    public function assertResponseStatus($status, $response)
+    public function assertResponseStatus($status, $response): void
     {
         $this->assertInstanceOf('yii\console\Response', $response);
         $this->assertSame($status, $response->exitStatus);
@@ -214,7 +215,7 @@ class ControllerTest extends TestCase
         return Yii::$app->handleRequest($request);
     }
 
-    public function testResponse()
+    public function testResponse(): void
     {
         $status = 123;
 
@@ -234,7 +235,7 @@ class ControllerTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/12028
      */
-    public function testHelpOptionNotSet()
+    public function testHelpOptionNotSet(): void
     {
         $controller = new FakeController('posts', Yii::$app);
         $controller->runAction('index');
@@ -246,7 +247,7 @@ class ControllerTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/12028
      */
-    public function testHelpOption()
+    public function testHelpOption(): void
     {
         $controller = new FakeController('posts', Yii::$app);
         $controller->help = true;
@@ -263,7 +264,7 @@ class ControllerTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/13071
      */
-    public function testHelpOptionWithModule()
+    public function testHelpOptionWithModule(): void
     {
         $controller = new FakeController('posts', new Module('news'));
         $controller->help = true;
@@ -276,7 +277,7 @@ class ControllerTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/19028
      */
-    public function testGetActionArgsHelp()
+    public function testGetActionArgsHelp(): void
     {
         $controller = new FakeController('fake', Yii::$app);
         $help = $controller->getActionArgsHelp($controller->createAction('aksi2'));
@@ -293,7 +294,7 @@ class ControllerTest extends TestCase
         $this->assertEquals('string', $help['value']['type']);
     }
 
-    public function testGetActionHelpSummaryOnNull()
+    public function testGetActionHelpSummaryOnNull(): void
     {
         $controller = new FakeController('fake', Yii::$app);
 
diff --git a/tests/framework/console/FakeController.php b/tests/framework/console/FakeController.php
index 670ab68076..540cd1a0b5 100644
--- a/tests/framework/console/FakeController.php
+++ b/tests/framework/console/FakeController.php
@@ -51,7 +51,7 @@ class FakeController extends Controller
         ];
     }
 
-    public function actionIndex()
+    public function actionIndex(): void
     {
         self::$_wasActionIndexCalled = true;
     }
diff --git a/tests/framework/console/FakeHelpController.php b/tests/framework/console/FakeHelpController.php
index 24277688c0..af28037d93 100644
--- a/tests/framework/console/FakeHelpController.php
+++ b/tests/framework/console/FakeHelpController.php
@@ -14,7 +14,7 @@ class FakeHelpController extends HelpController
 {
     private static $_actionIndexLastCallParams;
 
-    public function actionIndex($command = null)
+    public function actionIndex($command = null): void
     {
         self::$_actionIndexLastCallParams = func_get_args();
     }
diff --git a/tests/framework/console/RequestTest.php b/tests/framework/console/RequestTest.php
index 7704d13b62..af90715a47 100644
--- a/tests/framework/console/RequestTest.php
+++ b/tests/framework/console/RequestTest.php
@@ -187,7 +187,7 @@ class RequestTest extends TestCase
      * @param array $expected
      * @param array|null $expectedException
      */
-    public function testResolve($params, $expected, $expectedException = null)
+    public function testResolve($params, $expected, $expectedException = null): void
     {
         if (isset($expectedException)) {
             $this->expectException($expectedException[0]);
diff --git a/tests/framework/console/UnknownCommandExceptionTest.php b/tests/framework/console/UnknownCommandExceptionTest.php
index a7502593b2..179ba23d87 100644
--- a/tests/framework/console/UnknownCommandExceptionTest.php
+++ b/tests/framework/console/UnknownCommandExceptionTest.php
@@ -62,13 +62,13 @@ class UnknownCommandExceptionTest extends TestCase
      * @param string $command
      * @param array $expectedSuggestion
      */
-    public function testSuggestCommand($command, $expectedSuggestion)
+    public function testSuggestCommand($command, $expectedSuggestion): void
     {
         $exception = new UnknownCommandException($command, Yii::$app);
         $this->assertEquals($expectedSuggestion, $exception->getSuggestedAlternatives());
     }
 
-    public function testNameAndConstructor()
+    public function testNameAndConstructor(): void
     {
         $exception = new UnknownCommandException('test', Yii::$app);
         $this->assertEquals('Unknown command', $exception->getName());
diff --git a/tests/framework/console/controllers/AssetControllerTest.php b/tests/framework/console/controllers/AssetControllerTest.php
index 828bf7a785..86e36ba5ba 100644
--- a/tests/framework/console/controllers/AssetControllerTest.php
+++ b/tests/framework/console/controllers/AssetControllerTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\console\controllers;
 
+use Exception;
 use Yii;
 use yii\console\controllers\AssetController;
 use yii\helpers\ArrayHelper;
@@ -134,13 +135,13 @@ class AssetControllerTest extends TestCase
      * @param string $fileName output file name.
      * @param array[] $bundles asset bundles config.
      * @param array $config additional config parameters.
-     * @throws \Exception on failure.
+     * @throws Exception on failure.
      */
     protected function createCompressConfigFile($fileName, array $bundles, array $config = [])
     {
         $content = '<?php return ' . var_export($this->createCompressConfig($bundles, $config), true) . ';';
         if (file_put_contents($fileName, $content) <= 0) {
-            throw new \Exception("Unable to create file '{$fileName}'!");
+            throw new Exception("Unable to create file '{$fileName}'!");
         }
     }
 
@@ -149,7 +150,7 @@ class AssetControllerTest extends TestCase
      * @param string $fileRelativeName file name relative to [[testFilePath]]
      * @param string $content file content
      * @param string $fileBasePath base path for the created files, if not set [[testFilePath]] is used.
-     * @throws \Exception on failure.
+     * @throws Exception on failure.
      */
     protected function createAssetSourceFile($fileRelativeName, $content, $fileBasePath = null)
     {
@@ -159,7 +160,7 @@ class AssetControllerTest extends TestCase
         $fileFullName = $fileBasePath . DIRECTORY_SEPARATOR . $fileRelativeName;
         $this->createDir(dirname($fileFullName));
         if (file_put_contents($fileFullName, $content) <= 0) {
-            throw new \Exception("Unable to create file '{$fileFullName}'!");
+            throw new Exception("Unable to create file '{$fileFullName}'!");
         }
     }
 
@@ -248,7 +249,7 @@ EOL;
 
     // Tests :
 
-    public function testActionTemplate()
+    public function testActionTemplate(): void
     {
         $configFileName = $this->testFilePath . DIRECTORY_SEPARATOR . 'config.php';
         $this->runAssetControllerAction('template', [$configFileName]);
@@ -257,7 +258,7 @@ EOL;
         $this->assertIsArray($config, 'Invalid config created!');
     }
 
-    public function testActionCompress()
+    public function testActionCompress(): void
     {
         // Given :
         $cssFiles = [
@@ -337,7 +338,7 @@ EOL;
      *
      * @see https://github.com/yiisoft/yii2/issues/5194
      */
-    public function testCompressExternalAsset()
+    public function testCompressExternalAsset(): void
     {
         // Given :
         $externalAssetConfig = [
@@ -408,7 +409,7 @@ EOL;
      *
      * @see https://github.com/yiisoft/yii2/issues/7539
      */
-    public function testDetectCircularDependency()
+    public function testDetectCircularDependency(): void
     {
         // Given :
         $namespace = __NAMESPACE__;
@@ -571,7 +572,7 @@ EOL;
      * @param $outputFilePath
      * @param $expectedCssContent
      */
-    public function testAdjustCssUrl($cssContent, $inputFilePath, $outputFilePath, $expectedCssContent)
+    public function testAdjustCssUrl($cssContent, $inputFilePath, $outputFilePath, $expectedCssContent): void
     {
         $adjustedCssContent = $this->invokeAssetControllerMethod('adjustCssUrl', [$cssContent, $inputFilePath, $outputFilePath]);
 
@@ -618,7 +619,7 @@ EOL;
      * @param string $sourcePath
      * @param string $expectedRealPath
      */
-    public function testFindRealPath($sourcePath, $expectedRealPath)
+    public function testFindRealPath($sourcePath, $expectedRealPath): void
     {
         $expectedRealPath = str_replace(['/', '\\'], DIRECTORY_SEPARATOR, $expectedRealPath);
         $realPath = $this->invokeAssetControllerMethod('findRealPath', [$sourcePath]);
@@ -630,7 +631,7 @@ EOL;
      *
      * @see https://github.com/yiisoft/yii2/issues/9708
      */
-    public function testActionCompressDeleteSource()
+    public function testActionCompressDeleteSource(): void
     {
         // Given :
         $cssFiles = [
@@ -700,7 +701,7 @@ EOL;
      *
      * @see https://github.com/yiisoft/yii2/issues/10567
      */
-    public function testActionCompressOverrideAsExternal()
+    public function testActionCompressOverrideAsExternal(): void
     {
         // Given :
         $cssFiles = [
diff --git a/tests/framework/console/controllers/BaseMessageControllerTest.php b/tests/framework/console/controllers/BaseMessageControllerTest.php
index bb3c5d2cde..8b1f858c22 100644
--- a/tests/framework/console/controllers/BaseMessageControllerTest.php
+++ b/tests/framework/console/controllers/BaseMessageControllerTest.php
@@ -146,7 +146,7 @@ abstract class BaseMessageControllerTest extends TestCase
 
     // Tests:
 
-    public function testActionConfig()
+    public function testActionConfig(): void
     {
         $configFileName = $this->configFileName;
         $out = $this->runMessageControllerAction('config', [$configFileName]);
@@ -156,20 +156,20 @@ abstract class BaseMessageControllerTest extends TestCase
         );
     }
 
-    public function testActionConfigSubDir()
+    public function testActionConfigSubDir(): void
     {
         $configFileName = Yii::getAlias('@yiiunit/runtime/not_existing_subdir') . DIRECTORY_SEPARATOR . 'message_controller_test_config-' . md5(uniqid()) . '.php';
         $out = $this->runMessageControllerAction('config', [$configFileName]);
         $this->assertFileExists($configFileName, "Unable to create config file in subdirectory. Command output:\n\n" . $out);
     }
 
-    public function testConfigFileNotExist()
+    public function testConfigFileNotExist(): void
     {
         $this->expectException('yii\\console\\Exception');
         $this->runMessageControllerAction('extract', ['not_existing_file.php']);
     }
 
-    public function testCreateTranslation()
+    public function testCreateTranslation(): void
     {
         $category = 'test.category1';
         $message = 'test message';
@@ -188,7 +188,7 @@ abstract class BaseMessageControllerTest extends TestCase
     /**
      * @depends testCreateTranslation
      */
-    public function testNothingToSave()
+    public function testNothingToSave(): void
     {
         $category = 'test_category2';
         $message = 'test message';
@@ -208,7 +208,7 @@ abstract class BaseMessageControllerTest extends TestCase
     /**
      * @depends testCreateTranslation
      */
-    public function testMerge()
+    public function testMerge(): void
     {
         $category = 'test_category3';
 
@@ -237,7 +237,7 @@ abstract class BaseMessageControllerTest extends TestCase
     /**
      * @depends testMerge
      */
-    public function testMarkObsoleteMessages()
+    public function testMarkObsoleteMessages(): void
     {
         $category = 'category';
 
@@ -260,7 +260,7 @@ abstract class BaseMessageControllerTest extends TestCase
     /**
      * @depends testMerge
      */
-    public function removeObsoleteMessages()
+    public function removeObsoleteMessages(): void
     {
         $category = 'category';
 
@@ -282,7 +282,7 @@ abstract class BaseMessageControllerTest extends TestCase
     /**
      * @depends testMerge
      */
-    public function testMergeWithContentZero()
+    public function testMergeWithContentZero(): void
     {
         $category = 'test_category5';
 
@@ -320,7 +320,7 @@ abstract class BaseMessageControllerTest extends TestCase
     /**
      * @depends testCreateTranslation
      */
-    public function testMultipleTranslators()
+    public function testMultipleTranslators(): void
     {
         $category = 'test_category6';
 
@@ -352,7 +352,7 @@ abstract class BaseMessageControllerTest extends TestCase
     /**
      * @depends testCreateTranslation
      */
-    public function testMultipleCategories()
+    public function testMultipleCategories(): void
     {
         $category1 = 'category1';
         $category2 = 'category2';
@@ -389,7 +389,7 @@ abstract class BaseMessageControllerTest extends TestCase
         $this->assertArrayNotHasKey($message2, $messages2, "message2 found in category2. Command output:\n\n" . $out);
     }
 
-    public function testIgnoreCategories()
+    public function testIgnoreCategories(): void
     {
         $category1 = 'category1';
         $category2 = 'category2';
@@ -435,7 +435,7 @@ abstract class BaseMessageControllerTest extends TestCase
      *
      * @see https://github.com/yiisoft/yii2/issues/8286
      */
-    public function testCreateTranslationFromNested()
+    public function testCreateTranslationFromNested(): void
     {
         $category = 'test.category1';
         $mainMessage = 'main message';
@@ -456,7 +456,7 @@ abstract class BaseMessageControllerTest extends TestCase
      *
      * @see https://github.com/yiisoft/yii2/issues/11502
      */
-    public function testMissingLanguage()
+    public function testMissingLanguage(): void
     {
         $category = 'multiLangCategory';
         $mainMessage = 'multiLangMessage';
@@ -482,7 +482,7 @@ abstract class BaseMessageControllerTest extends TestCase
      *
      * @see https://github.com/yiisoft/yii2/issues/13824
      */
-    public function testCreateTranslationFromConcatenatedString()
+    public function testCreateTranslationFromConcatenatedString(): void
     {
         $category = 'test.category1';
         $mainMessage = 'main message second message third message';
@@ -503,7 +503,7 @@ abstract class BaseMessageControllerTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/14016
      */
-    public function testShouldNotMarkUnused()
+    public function testShouldNotMarkUnused(): void
     {
         $category = 'testShouldNotMarkUnused';
 
@@ -538,7 +538,7 @@ abstract class BaseMessageControllerTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/13792
      */
-    public function testShouldNotRemoveUnused()
+    public function testShouldNotRemoveUnused(): void
     {
         $category = 'my';
 
@@ -576,7 +576,7 @@ abstract class BaseMessageControllerTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/16828
      */
-    public function testPartialTranslator()
+    public function testPartialTranslator(): void
     {
         $category = 'category';
         $negativeKey1 = 'Should not find this';
@@ -610,7 +610,7 @@ abstract class BaseMessageControllerTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/17098
      */
-    public function testMessageExtractActionWhenMessageUsingParamsReturnedFromMethodCalls()
+    public function testMessageExtractActionWhenMessageUsingParamsReturnedFromMethodCalls(): void
     {
         $sourceFileContent = "
             echo PHP_EOL, Yii::t('app', '1. Simple message');
@@ -653,7 +653,7 @@ abstract class BaseMessageControllerTest extends TestCase
         ], $messages);
     }
 
-    public function testMessagesSorting()
+    public function testMessagesSorting(): void
     {
         $category = 'test_order_category';
         $key1 = 'key1';
diff --git a/tests/framework/console/controllers/CacheControllerTest.php b/tests/framework/console/controllers/CacheControllerTest.php
index a77d9d8334..d1c5d55219 100644
--- a/tests/framework/console/controllers/CacheControllerTest.php
+++ b/tests/framework/console/controllers/CacheControllerTest.php
@@ -85,7 +85,7 @@ class CacheControllerTest extends TestCase
         }
     }
 
-    public function testFlushOne()
+    public function testFlushOne(): void
     {
         Yii::$app->firstCache->set('firstKey', 'firstValue');
         Yii::$app->firstCache->set('secondKey', 'secondValue');
@@ -98,7 +98,7 @@ class CacheControllerTest extends TestCase
         $this->assertEquals('thirdValue', Yii::$app->secondCache->get('thirdKey'), 'second cache data should not be flushed');
     }
 
-    public function testClearSchema()
+    public function testClearSchema(): void
     {
         $schema = Yii::$app->db->schema;
         Yii::$app->db->createCommand()->createTable('test_schema_cache', ['id' => 'pk'])->execute();
@@ -116,7 +116,7 @@ class CacheControllerTest extends TestCase
         $this->assertEquals($noCacheSchemas, $cacheSchema, 'Schema cache should be flushed.');
     }
 
-    public function testFlushBoth()
+    public function testFlushBoth(): void
     {
         Yii::$app->firstCache->set('firstKey', 'firstValue');
         Yii::$app->firstCache->set('secondKey', 'secondValue');
@@ -129,7 +129,7 @@ class CacheControllerTest extends TestCase
         $this->assertFalse(Yii::$app->secondCache->get('thirdKey'), 'second cache data should be flushed');
     }
 
-    public function testNotFoundFlush()
+    public function testNotFoundFlush(): void
     {
         Yii::$app->firstCache->set('firstKey', 'firstValue');
 
@@ -138,7 +138,7 @@ class CacheControllerTest extends TestCase
         $this->assertEquals('firstValue', Yii::$app->firstCache->get('firstKey'), 'first cache data should not be flushed');
     }
 
-    public function testNothingToFlushException()
+    public function testNothingToFlushException(): void
     {
         $this->expectException('yii\console\Exception');
         $this->expectExceptionMessage('You should specify cache components names');
@@ -146,7 +146,7 @@ class CacheControllerTest extends TestCase
         $this->_cacheController->actionFlush();
     }
 
-    public function testFlushAll()
+    public function testFlushAll(): void
     {
         Yii::$app->firstCache->set('firstKey', 'firstValue');
         Yii::$app->secondCache->set('secondKey', 'secondValue');
diff --git a/tests/framework/console/controllers/DbMessageControllerTest.php b/tests/framework/console/controllers/DbMessageControllerTest.php
index d685f3bad9..17d6c89c49 100644
--- a/tests/framework/console/controllers/DbMessageControllerTest.php
+++ b/tests/framework/console/controllers/DbMessageControllerTest.php
@@ -8,6 +8,14 @@
 
 namespace yiiunit\framework\console\controllers;
 
+use yii\console\Application;
+use yii\console\Controller;
+use yii\helpers\ArrayHelper;
+use yii\db\Query;
+use yii\db\Expression;
+use yii\base\InvalidParamException;
+use yii\db\Exception;
+use yii\base\InvalidConfigException;
 use Yii;
 use yii\db\Connection;
 
@@ -30,7 +38,7 @@ class DbMessageControllerTest extends BaseMessageControllerTest
     protected static function runConsoleAction($route, $params = [])
     {
         if (Yii::$app === null) {
-            new \yii\console\Application([
+            new Application([
                 'id' => 'Migrator',
                 'basePath' => '@yiiunit',
                 'controllerMap' => [
@@ -45,7 +53,7 @@ class DbMessageControllerTest extends BaseMessageControllerTest
         ob_start();
         $result = Yii::$app->runAction($route, $params);
         echo 'Result is ' . $result;
-        if ($result !== \yii\console\Controller::EXIT_CODE_NORMAL) {
+        if ($result !== Controller::EXIT_CODE_NORMAL) {
             ob_end_flush();
         } else {
             ob_end_clean();
@@ -83,10 +91,10 @@ class DbMessageControllerTest extends BaseMessageControllerTest
     }
 
     /**
-     * @throws \yii\base\InvalidParamException
-     * @throws \yii\db\Exception
-     * @throws \yii\base\InvalidConfigException
-     * @return \yii\db\Connection
+     * @throws InvalidParamException
+     * @throws Exception
+     * @throws InvalidConfigException
+     * @return Connection
      */
     public static function getConnection()
     {
@@ -150,11 +158,11 @@ class DbMessageControllerTest extends BaseMessageControllerTest
      */
     protected function loadMessages($category)
     {
-        return \yii\helpers\ArrayHelper::map((new \yii\db\Query())
+        return ArrayHelper::map((new Query())
             ->select(['message' => 't1.message', 'translation' => 't2.translation'])
             ->from(['t1' => 'source_message', 't2' => 'message'])
             ->where([
-                't1.id' => new \yii\db\Expression('[[t2.id]]'),
+                't1.id' => new Expression('[[t2.id]]'),
                 't1.category' => $category,
                 't2.language' => $this->language,
             ])->all(static::$db), 'message', 'translation');
@@ -166,7 +174,7 @@ class DbMessageControllerTest extends BaseMessageControllerTest
      * Source is marked instead of translation.
      * @depends testMerge
      */
-    public function testMarkObsoleteMessages()
+    public function testMarkObsoleteMessages(): void
     {
         $category = 'category';
 
@@ -188,7 +196,7 @@ class DbMessageControllerTest extends BaseMessageControllerTest
         $this->assertEquals($obsoleteTranslation, $messages[$obsoleteMessage], "Obsolete message was not marked properly. Command output:\n\n" . $out);
     }
 
-    public function testMessagesSorting()
+    public function testMessagesSorting(): void
     {
         $this->markTestSkipped('There\'s no need to order messages for database');
     }
diff --git a/tests/framework/console/controllers/EchoMigrateController.php b/tests/framework/console/controllers/EchoMigrateController.php
index 2eefd60267..5320235b6a 100644
--- a/tests/framework/console/controllers/EchoMigrateController.php
+++ b/tests/framework/console/controllers/EchoMigrateController.php
@@ -18,7 +18,7 @@ class EchoMigrateController extends MigrateController
     /**
      * {@inheritdoc}
      */
-    public function stdout($string)
+    public function stdout($string): void
     {
         echo $string;
     }
diff --git a/tests/framework/console/controllers/FixtureControllerTest.php b/tests/framework/console/controllers/FixtureControllerTest.php
index bb912efb9d..c2350c30d0 100644
--- a/tests/framework/console/controllers/FixtureControllerTest.php
+++ b/tests/framework/console/controllers/FixtureControllerTest.php
@@ -25,7 +25,7 @@ use yiiunit\framework\db\DatabaseTestCase;
 class FixtureControllerTest extends DatabaseTestCase
 {
     /**
-     * @var \yiiunit\framework\console\controllers\FixtureConsoledController
+     * @var FixtureConsoledController
      */
     private $_fixtureController;
 
@@ -36,7 +36,7 @@ class FixtureControllerTest extends DatabaseTestCase
         parent::setUp();
 
         $db = $this->getConnection();
-        \Yii::$app->set('db', $db);
+        Yii::$app->set('db', $db);
         ActiveRecord::$db = $db;
 
         $this->_fixtureController = Yii::createObject([
@@ -55,7 +55,7 @@ class FixtureControllerTest extends DatabaseTestCase
         parent::tearDown();
     }
 
-    public function testLoadGlobalFixture()
+    public function testLoadGlobalFixture(): void
     {
         $this->_fixtureController->globalFixtures = [
             '\yiiunit\data\console\controllers\fixtures\Global',
@@ -67,7 +67,7 @@ class FixtureControllerTest extends DatabaseTestCase
         $this->assertCount(1, FixtureStorage::$firstFixtureData, 'first fixture data should be loaded');
     }
 
-    public function testLoadGlobalFixtureWithFixture()
+    public function testLoadGlobalFixtureWithFixture(): void
     {
         $this->_fixtureController->globalFixtures = [
             '\yiiunit\data\console\controllers\fixtures\GlobalFixture',
@@ -79,7 +79,7 @@ class FixtureControllerTest extends DatabaseTestCase
         $this->assertCount(1, FixtureStorage::$firstFixtureData, 'first fixture data should be loaded');
     }
 
-    public function testUnloadGlobalFixture()
+    public function testUnloadGlobalFixture(): void
     {
         $this->_fixtureController->globalFixtures = [
             '\yiiunit\data\console\controllers\fixtures\Global',
@@ -97,7 +97,7 @@ class FixtureControllerTest extends DatabaseTestCase
         $this->assertEmpty(FixtureStorage::$firstFixtureData, 'first fixture data should be unloaded');
     }
 
-    public function testLoadAll()
+    public function testLoadAll(): void
     {
         $this->assertEmpty(FixtureStorage::$globalFixturesData, 'global fixture data should be empty');
         $this->assertEmpty(FixtureStorage::$firstFixtureData, 'first fixture data should be empty');
@@ -114,7 +114,7 @@ class FixtureControllerTest extends DatabaseTestCase
         $this->assertCount(1, FixtureStorage::$subdirSecondFixtureData, 'subdir / second fixture data should be loaded');
     }
 
-    public function testUnloadAll()
+    public function testUnloadAll(): void
     {
         FixtureStorage::$globalFixturesData[] = 'some seeded global fixture data';
         FixtureStorage::$firstFixtureData[] = 'some seeded first fixture data';
@@ -137,7 +137,7 @@ class FixtureControllerTest extends DatabaseTestCase
         $this->assertEmpty(FixtureStorage::$subdirSecondFixtureData, 'subdir/second fixture data should be unloaded');
     }
 
-    public function testLoadParticularExceptOnes()
+    public function testLoadParticularExceptOnes(): void
     {
         $this->_fixtureController->actionLoad(['First', 'subdir/First', '-Second', '-Global', '-subdir/Second']);
 
@@ -148,7 +148,7 @@ class FixtureControllerTest extends DatabaseTestCase
         $this->assertEmpty(FixtureStorage::$subdirSecondFixtureData, 'subdir/second fixture data should not be loaded');
     }
 
-    public function testUnloadParticularExceptOnes()
+    public function testUnloadParticularExceptOnes(): void
     {
         FixtureStorage::$globalFixturesData[] = 'some seeded global fixture data';
         FixtureStorage::$firstFixtureData[] = 'some seeded first fixture data';
@@ -171,7 +171,7 @@ class FixtureControllerTest extends DatabaseTestCase
         $this->assertNotEmpty(FixtureStorage::$subdirSecondFixtureData, 'subdir/second fixture data should not be unloaded');
     }
 
-    public function testLoadAllExceptOnes()
+    public function testLoadAllExceptOnes(): void
     {
         $this->_fixtureController->actionLoad(['*', '-Second', '-Global', '-subdir/First']);
 
@@ -182,7 +182,7 @@ class FixtureControllerTest extends DatabaseTestCase
         $this->assertEmpty(FixtureStorage::$subdirFirstFixtureData, 'subdir/first fixture data should not be loaded');
     }
 
-    public function testUnloadAllExceptOnes()
+    public function testUnloadAllExceptOnes(): void
     {
         FixtureStorage::$globalFixturesData[] = 'some seeded global fixture data';
         FixtureStorage::$firstFixtureData[] = 'some seeded first fixture data';
@@ -199,7 +199,7 @@ class FixtureControllerTest extends DatabaseTestCase
         $this->assertNotEmpty(FixtureStorage::$subdirFirstFixtureData, 'subdir/first fixture data should not be unloaded');
     }
 
-    public function testNothingToLoadParticularExceptOnes()
+    public function testNothingToLoadParticularExceptOnes(): void
     {
         $this->_fixtureController->actionLoad(['First', '-First']);
 
@@ -209,26 +209,26 @@ class FixtureControllerTest extends DatabaseTestCase
         );
     }
 
-    public function testNothingToUnloadParticularExceptOnes()
+    public function testNothingToUnloadParticularExceptOnes(): void
     {
         $this->_fixtureController->actionUnload(['First', '-First']);
 
         $this->assertEmpty(FixtureStorage::$firstFixtureData, 'first fixture data should not be loaded');
     }
 
-    public function testNoFixturesWereFoundInLoad()
+    public function testNoFixturesWereFoundInLoad(): void
     {
         $this->expectException('\yii\console\Exception');
         $this->_fixtureController->actionLoad(['NotExistingFixture']);
     }
 
-    public function testNoFixturesWereFoundInUnload()
+    public function testNoFixturesWereFoundInUnload(): void
     {
         $this->expectException('\yii\console\Exception');
         $this->_fixtureController->actionUnload(['NotExistingFixture']);
     }
 
-    public function testLoadActiveFixtureSequence()
+    public function testLoadActiveFixtureSequence(): void
     {
         $this->assertEmpty(FixtureStorage::$activeFixtureSequence, 'Active fixture sequence should be empty.');
 
diff --git a/tests/framework/console/controllers/HelpControllerTest.php b/tests/framework/console/controllers/HelpControllerTest.php
index 7377716de0..39d4cf3aa1 100644
--- a/tests/framework/console/controllers/HelpControllerTest.php
+++ b/tests/framework/console/controllers/HelpControllerTest.php
@@ -54,7 +54,7 @@ class HelpControllerTest extends TestCase
         return $controller->flushStdOutBuffer();
     }
 
-    public function testModuleControllersList()
+    public function testModuleControllersList(): void
     {
         $this->mockApplication([
             'enableCoreCommands' => false,
@@ -77,7 +77,7 @@ STRING
             , $result);
     }
 
-    public function testActionList()
+    public function testActionList(): void
     {
         $this->mockApplication([
             'enableCoreCommands' => false,
@@ -113,7 +113,7 @@ STRING
             , $result);
     }
 
-    public function testActionListActionOptions()
+    public function testActionListActionOptions(): void
     {
         $this->mockApplication([
             'enableCoreCommands' => false,
@@ -135,7 +135,7 @@ STRING
             , $result);
     }
 
-    public function testActionUsage()
+    public function testActionUsage(): void
     {
         $this->mockApplication([
             'enableCoreCommands' => false,
@@ -152,7 +152,7 @@ STRING
             , $result);
     }
 
-    public function testActionIndex()
+    public function testActionIndex(): void
     {
         $result = Console::stripAnsiFormat($this->runControllerAction('index'));
         $this->assertStringContainsString('This is Yii version ', $result);
@@ -161,7 +161,7 @@ STRING
         $this->assertStringContainsString('bootstrap.php help', $result);
     }
 
-    public function testActionIndexWithHelpCommand()
+    public function testActionIndexWithHelpCommand(): void
     {
         $result = Console::stripAnsiFormat($this->runControllerAction('index', ['command' => 'help/index']));
         $this->assertStringContainsString('Displays available commands or the detailed information', $result);
@@ -173,7 +173,7 @@ STRING
         $this->assertStringContainsString('--interactive: boolean, 0 or 1 (defaults to 1)', $result);
     }
 
-    public function testActionIndexWithServeCommand()
+    public function testActionIndexWithServeCommand(): void
     {
         $result = Console::stripAnsiFormat($this->runControllerAction('index', ['command' => 'serve']));
         $this->assertStringContainsString('Runs PHP built-in web server', $result);
@@ -188,7 +188,7 @@ STRING
         $this->assertStringContainsString('--router, -r: string', $result);
     }
 
-    public function testActionListContainsNoEmptyCommands()
+    public function testActionListContainsNoEmptyCommands(): void
     {
         $this->mockApplication([
             'enableCoreCommands' => false,
@@ -200,7 +200,7 @@ STRING
         $this->assertStringContainsString("fake-no-default/index\n", $result);
     }
 
-    public function testActionIndexContainsNoEmptyCommands()
+    public function testActionIndexContainsNoEmptyCommands(): void
     {
         $this->mockApplication([
             'enableCoreCommands' => false,
diff --git a/tests/framework/console/controllers/MigrateControllerTest.php b/tests/framework/console/controllers/MigrateControllerTest.php
index 20f41abfe6..71cdb1fb60 100644
--- a/tests/framework/console/controllers/MigrateControllerTest.php
+++ b/tests/framework/console/controllers/MigrateControllerTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\console\controllers;
 
+use yii\db\Exception;
 use Yii;
 use yii\console\controllers\MigrateController;
 use yii\console\ExitCode;
@@ -60,7 +61,7 @@ class MigrateControllerTest extends TestCase
         return $query->from('migration')->all();
     }
 
-    public function assertFileContent($expectedFile, $class, $table, $namespace = null)
+    public function assertFileContent($expectedFile, $class, $table, $namespace = null): void
     {
         if ($namespace) {
             $namespace = "namespace {$namespace};\n\n";
@@ -95,7 +96,7 @@ class MigrateControllerTest extends TestCase
         $this->assertFileContent($expectedFile, $class, $table, $namespace);
     }
 
-    public function assertFileContentJunction($expectedFile, $class, $junctionTable, $firstTable, $secondTable, $namespace = null)
+    public function assertFileContentJunction($expectedFile, $class, $junctionTable, $firstTable, $secondTable, $namespace = null): void
     {
         if ($namespace) {
             $namespace = "namespace {$namespace};\n\n";
@@ -341,7 +342,7 @@ class MigrateControllerTest extends TestCase
      * @param array $params
      * @dataProvider generateMigrationDataProvider
      */
-    public function testGenerateMigration($expectedFile, $migrationName, $table, $params)
+    public function testGenerateMigration($expectedFile, $migrationName, $table, $params): void
     {
         $this->migrationNamespace = 'yiiunit\runtime\test_migrations';
 
@@ -386,7 +387,7 @@ class MigrateControllerTest extends TestCase
      * @param string $secondTable
      * @dataProvider generateJunctionMigrationDataProvider
      */
-    public function testGenerateJunctionMigration($migrationName, $junctionTable, $firstTable, $secondTable)
+    public function testGenerateJunctionMigration($migrationName, $junctionTable, $firstTable, $secondTable): void
     {
         $this->migrationNamespace = 'yiiunit\runtime\test_migrations';
 
@@ -413,7 +414,7 @@ class MigrateControllerTest extends TestCase
         );
     }
 
-    public function testUpdatingLongNamedMigration()
+    public function testUpdatingLongNamedMigration(): void
     {
         $this->createMigration(str_repeat('a', 180));
 
@@ -424,7 +425,7 @@ class MigrateControllerTest extends TestCase
         $this->assertStringContainsString('is too long. Its not possible to apply this migration.', $result);
     }
 
-    public function testNamedMigrationWithCustomLimit()
+    public function testNamedMigrationWithCustomLimit(): void
     {
         Yii::$app->db->createCommand()->createTable('migration', [
             'version' => 'varchar(255) NOT NULL PRIMARY KEY', // varchar(255) is longer than the default of 180
@@ -440,7 +441,7 @@ class MigrateControllerTest extends TestCase
         $this->assertStringContainsString('Migrated up successfully.', $result);
     }
 
-    public function testCreateLongNamedMigration()
+    public function testCreateLongNamedMigration(): void
     {
         $this->setOutputCallback(function ($output) {
             return null;
@@ -460,9 +461,9 @@ class MigrateControllerTest extends TestCase
      * Test the migrate:fresh command.
      * @dataProvider refreshMigrationDataProvider
      * @param $db
-     * @throws \yii\db\Exception
+     * @throws Exception
      */
-    public function testRefreshMigration($db)
+    public function testRefreshMigration($db): void
     {
         if ($db !== 'default') {
             $this->switchDbConnection($db);
@@ -497,7 +498,7 @@ class MigrateControllerTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/12980
      */
-    public function testGetMigrationHistory()
+    public function testGetMigrationHistory(): void
     {
         $controllerConfig = [
             'migrationPath' => null,
diff --git a/tests/framework/console/controllers/MigrateControllerTestTrait.php b/tests/framework/console/controllers/MigrateControllerTestTrait.php
index 320f220bc7..db301b48bf 100644
--- a/tests/framework/console/controllers/MigrateControllerTestTrait.php
+++ b/tests/framework/console/controllers/MigrateControllerTestTrait.php
@@ -49,7 +49,7 @@ trait MigrateControllerTestTrait
         return $this->migrationExitCode;
     }
 
-    public function setUpMigrationPath()
+    public function setUpMigrationPath(): void
     {
         $this->migrationNamespace = 'yiiunit\runtime\test_migrations';
         $this->migrationPath = Yii::getAlias('@yiiunit/runtime/test_migrations');
@@ -59,7 +59,7 @@ trait MigrateControllerTestTrait
         }
     }
 
-    public function tearDownMigrationPath()
+    public function tearDownMigrationPath(): void
     {
         FileHelper::removeDirectory($this->migrationPath);
         FileHelper::removeDirectory(Yii::getAlias('@yiiunit/runtime/app_migrations'));
@@ -221,7 +221,7 @@ CODE;
 
     // Tests :
 
-    public function testCreate()
+    public function testCreate(): void
     {
         $migrationName = 'test_migration';
         $this->runMigrateControllerAction('create', [$migrationName]);
@@ -231,7 +231,7 @@ CODE;
         $this->assertStringContainsString($migrationName, basename($files[0]), 'Wrong migration name!');
     }
 
-    public function testUp()
+    public function testUp(): void
     {
         $this->createMigration('test_up1');
         $this->createMigration('test_up2');
@@ -245,7 +245,7 @@ CODE;
     /**
      * @depends testUp
      */
-    public function testUpCount()
+    public function testUpCount(): void
     {
         $this->createMigration('test_down1');
         $this->createMigration('test_down2');
@@ -259,7 +259,7 @@ CODE;
     /**
      * @depends testUp
      */
-    public function testDownCount()
+    public function testDownCount(): void
     {
         $this->createMigration('test_down_count1');
         $this->createMigration('test_down_count2');
@@ -275,7 +275,7 @@ CODE;
     /**
      * @depends testDownCount
      */
-    public function testDownAll()
+    public function testDownAll(): void
     {
         $this->createMigration('test_down_all1');
         $this->createMigration('test_down_all2');
@@ -291,7 +291,7 @@ CODE;
     /**
      * @depends testUp
      */
-    public function testHistory()
+    public function testHistory(): void
     {
         $output = $this->runMigrateControllerAction('history');
         $this->assertStringContainsString('No migration', $output);
@@ -310,7 +310,7 @@ CODE;
     /**
      * @depends testUp
      */
-    public function testNew()
+    public function testNew(): void
     {
         $this->createMigration('test_new1');
 
@@ -326,7 +326,7 @@ CODE;
         $this->assertStringNotContainsString('_test_new1', $output);
     }
 
-    public function testMark()
+    public function testMark(): void
     {
         $version = '010101_000001';
         $this->createMigration('test_mark1', $version);
@@ -337,7 +337,7 @@ CODE;
         $this->assertMigrationHistory(['m*_base', 'm*_test_mark1']);
     }
 
-    public function testMarkBase()
+    public function testMarkBase(): void
     {
         $version = '010101_000001';
         $this->createMigration('test_mark1', $version);
@@ -351,7 +351,7 @@ CODE;
         $this->assertMigrationHistory(['m*_base']);
     }
 
-    public function testTo()
+    public function testTo(): void
     {
         $version = '020202_000001';
         $this->createMigration('to1', $version);
@@ -365,7 +365,7 @@ CODE;
     /**
      * @depends testUp
      */
-    public function testRedo()
+    public function testRedo(): void
     {
         $this->createMigration('test_redo1');
         $this->runMigrateControllerAction('up');
@@ -382,7 +382,7 @@ CODE;
     /**
      * @depends testCreate
      */
-    public function testNamespaceCreate()
+    public function testNamespaceCreate(): void
     {
         // default namespace apply :
         $migrationName = 'testDefaultNamespace';
@@ -424,7 +424,7 @@ CODE;
     /**
      * @depends testUp
      */
-    public function testNamespaceUp()
+    public function testNamespaceUp(): void
     {
         $this->createNamespaceMigration('nsTest1');
         $this->createNamespaceMigration('nsTest2');
@@ -446,7 +446,7 @@ CODE;
      * @depends testNamespaceUp
      * @depends testDownCount
      */
-    public function testNamespaceDownCount()
+    public function testNamespaceDownCount(): void
     {
         $this->createNamespaceMigration('down1');
         $this->createNamespaceMigration('down2');
@@ -470,7 +470,7 @@ CODE;
      * @depends testNamespaceUp
      * @depends testHistory
      */
-    public function testNamespaceHistory()
+    public function testNamespaceHistory(): void
     {
         $controllerConfig = [
             'migrationPath' => null,
@@ -494,7 +494,7 @@ CODE;
     /**
      * @depends testMark
      */
-    public function testNamespaceMark()
+    public function testNamespaceMark(): void
     {
         $controllerConfig = [
             'migrationPath' => null,
@@ -513,7 +513,7 @@ CODE;
     /**
      * @depends testTo
      */
-    public function testNamespaceTo()
+    public function testNamespaceTo(): void
     {
         $controllerConfig = [
             'migrationPath' => null,
@@ -532,7 +532,7 @@ CODE;
     /**
      * Test migration with using multiple migration paths and namespaces.
      */
-    public function testCombinedMigrationProcess()
+    public function testCombinedMigrationProcess(): void
     {
         FileHelper::createDirectory(Yii::getAlias('@yiiunit/runtime/app_migrations'));
         FileHelper::createDirectory(Yii::getAlias('@yiiunit/runtime/extension_migrations'));
diff --git a/tests/framework/console/controllers/PHPMessageControllerTest.php b/tests/framework/console/controllers/PHPMessageControllerTest.php
index f67d464296..9551eecce2 100644
--- a/tests/framework/console/controllers/PHPMessageControllerTest.php
+++ b/tests/framework/console/controllers/PHPMessageControllerTest.php
@@ -99,7 +99,7 @@ class PHPMessageControllerTest extends BaseMessageControllerTest
     // By default phpunit runs inherited test after inline tests, so `testCreateTranslation()` would be run after
     // `testCustomFileHeaderAndDocBlock()` (that would break `@depends` annotation). This ensures that
     // `testCreateTranslation() will be run before `testCustomFileHeaderAndDocBlock()`.
-    public function testCreateTranslation()
+    public function testCreateTranslation(): void
     {
         parent::testCreateTranslation();
     }
@@ -107,7 +107,7 @@ class PHPMessageControllerTest extends BaseMessageControllerTest
     /**
      * @depends testCreateTranslation
      */
-    public function testCustomFileHeaderAndDocBlock()
+    public function testCustomFileHeaderAndDocBlock(): void
     {
         $category = 'test_headers_category';
         $message = 'test message';
@@ -148,7 +148,7 @@ class PHPMessageControllerTest extends BaseMessageControllerTest
     /**
      * @dataProvider messageFileCategoriesDataProvider
      */
-    public function testRemoveUnusedBehavior($category, $isUnused, $removeUnused, $isExpectedToExist)
+    public function testRemoveUnusedBehavior($category, $isUnused, $removeUnused, $isExpectedToExist): void
     {
         $this->saveMessages(['test message' => 'test translation'], $category);
         $filePath = $this->getMessageFilePath($category);
diff --git a/tests/framework/console/controllers/ServeControllerTest.php b/tests/framework/console/controllers/ServeControllerTest.php
index 1c6eb7b973..a57a195ba9 100644
--- a/tests/framework/console/controllers/ServeControllerTest.php
+++ b/tests/framework/console/controllers/ServeControllerTest.php
@@ -25,7 +25,7 @@ class ServeControllerTest extends TestCase
         $this->mockApplication();
     }
 
-    public function testAddressTaken()
+    public function testAddressTaken(): void
     {
         $docroot = __DIR__ . '/stub';
 
@@ -50,7 +50,7 @@ class ServeControllerTest extends TestCase
         $this->assertStringContainsString('http://localhost:8080 is taken by another process.', $result);
     }
 
-    public function testDefaultValues()
+    public function testDefaultValues(): void
     {
         $docroot = __DIR__ . '/stub';
 
@@ -76,7 +76,7 @@ class ServeControllerTest extends TestCase
         $this->assertStringContainsString('Quit the server with CTRL-C or COMMAND-C.', $result);
     }
 
-    public function testDoocRootWithNoExistValue()
+    public function testDoocRootWithNoExistValue(): void
     {
         $docroot = '/not/exist/path';
 
@@ -99,7 +99,7 @@ class ServeControllerTest extends TestCase
         $this->assertStringContainsString("Document root \"{$docroot}\" does not exist.", $result);
     }
 
-    public function testWithRouterNoExistValue()
+    public function testWithRouterNoExistValue(): void
     {
         $docroot = __DIR__ . '/stub';
         $router = '/not/exist/path';
@@ -125,7 +125,7 @@ class ServeControllerTest extends TestCase
         $this->assertStringContainsString("Routing file \"$router\" does not exist.", $result);
     }
 
-    public function testWithRouterValue()
+    public function testWithRouterValue(): void
     {
         $docroot = __DIR__ . '/stub';
         $router = __DIR__ . '/stub/index.php';
diff --git a/tests/framework/console/controllers/SilencedCacheController.php b/tests/framework/console/controllers/SilencedCacheController.php
index 659e324048..dbf05c1ca4 100644
--- a/tests/framework/console/controllers/SilencedCacheController.php
+++ b/tests/framework/console/controllers/SilencedCacheController.php
@@ -18,7 +18,7 @@ class SilencedCacheController extends CacheController
     /**
      * {@inheritdoc}
      */
-    public function stdout($string)
+    public function stdout($string): void
     {
         // do nothing
     }
diff --git a/tests/framework/console/controllers/StdOutBufferControllerTrait.php b/tests/framework/console/controllers/StdOutBufferControllerTrait.php
index 90593ef01f..92ca9ca0ef 100644
--- a/tests/framework/console/controllers/StdOutBufferControllerTrait.php
+++ b/tests/framework/console/controllers/StdOutBufferControllerTrait.php
@@ -19,7 +19,7 @@ trait StdOutBufferControllerTrait
      */
     private $stdOutBuffer = '';
 
-    public function stdout($string)
+    public function stdout($string): void
     {
         $this->stdOutBuffer .= $string;
     }
diff --git a/tests/framework/console/widgets/TableTest.php b/tests/framework/console/widgets/TableTest.php
index 1889521cda..431f1afcf7 100644
--- a/tests/framework/console/widgets/TableTest.php
+++ b/tests/framework/console/widgets/TableTest.php
@@ -46,7 +46,7 @@ class TableTest extends TestCase
     /**
      * @dataProvider getTableData
      */
-    public function testTable($headers, $rows)
+    public function testTable($headers, $rows): void
     {
         $table = new Table();
 
@@ -110,7 +110,7 @@ EXPECTED;
     /**
      * @dataProvider getMultiLineTableData
      */
-    public function testMultiLineTable($headers, $rows)
+    public function testMultiLineTable($headers, $rows): void
     {
         $table = new Table();
 
@@ -161,7 +161,7 @@ EXPECTED;
     /**
      * @dataProvider getNumericTableData
      */
-    public function testNumericTable($headers, $rows)
+    public function testNumericTable($headers, $rows): void
     {
         $table = new Table();
 
@@ -184,7 +184,7 @@ EXPECTED;
         $this->assertEqualsWithoutLE($expected, $tableContent);
     }
 
-    public function testTableWithFullwidthChars()
+    public function testTableWithFullwidthChars(): void
     {
         $table = new Table();
 
@@ -211,7 +211,7 @@ EXPECTED;
         );
     }
 
-    public function testLists()
+    public function testLists(): void
     {
         $table = new Table();
 
@@ -238,7 +238,7 @@ EXPECTED;
         );
     }
 
-    public function testListPrefix()
+    public function testListPrefix(): void
     {
         $table = new Table();
 
@@ -264,7 +264,7 @@ EXPECTED;
         );
     }
 
-    public function testLongerListPrefix()
+    public function testLongerListPrefix(): void
     {
         $table = new Table();
 
@@ -295,7 +295,7 @@ EXPECTED;
         );
     }
 
-    public function testCustomChars()
+    public function testCustomChars(): void
     {
         $table = new Table();
 
@@ -336,7 +336,7 @@ EXPECTED;
         );
     }
 
-    public function testTableWidgetSyntax()
+    public function testTableWidgetSyntax(): void
     {
         $expected = <<<'EXPECTED'
 ╔═══════════════╤═══════════════╤═══════════════╗
@@ -362,7 +362,7 @@ EXPECTED;
         );
     }
 
-    public function testShortRow()
+    public function testShortRow(): void
     {
         $table = new Table();
 
@@ -396,7 +396,7 @@ EXPECTED;
         );
     }
 
-    public function testEmptyRow()
+    public function testEmptyRow(): void
     {
         $table = new Table();
 
@@ -421,7 +421,7 @@ EXPECTED;
         );
     }
 
-    public function testEmptyHeaders()
+    public function testEmptyHeaders(): void
     {
         $table = new Table();
 
@@ -443,7 +443,7 @@ EXPECTED;
         );
     }
 
-    public function testEmptyTable()
+    public function testEmptyTable(): void
     {
         $table = new Table();
 
@@ -461,7 +461,7 @@ EXPECTED;
         );
     }
 
-    public function testEmptyAndZeroTableCell()
+    public function testEmptyAndZeroTableCell(): void
     {
         $table = new Table();
 
@@ -489,7 +489,7 @@ EXPECTED;
         );
     }
 
-    public function testColorizedInput()
+    public function testColorizedInput(): void
     {
         $table = new Table();
 
@@ -518,7 +518,7 @@ EXPECTED;
         );
     }
 
-    public function testColorizedInputStripsANSIMarkersInternally()
+    public function testColorizedInputStripsANSIMarkersInternally(): void
     {
         $table = new Table();
 
@@ -539,7 +539,7 @@ EXPECTED;
         $this->assertEquals(8 + 2, $columnWidths[2]);
     }
 
-    public function testCalculateRowHeightShouldNotThrowDivisionByZeroException()
+    public function testCalculateRowHeightShouldNotThrowDivisionByZeroException(): void
     {
         $rows = [
             ['XXXXXX', 'XXXXXXXXXXXXXXXXXXXX', '', '', 'XXXXXXXXXXXXXXXXXX', 'X', 'XXX'],
@@ -554,7 +554,7 @@ EXPECTED;
         $this->assertEqualsWithoutLE($table, $table);
     }
 
-    public function testLineBreakTableCell()
+    public function testLineBreakTableCell(): void
     {
         $table = new Table();
 
@@ -589,7 +589,7 @@ EXPECTED;
         );
     }
 
-    public function testColorizedLineBreakTableCell()
+    public function testColorizedLineBreakTableCell(): void
     {
         $table = new Table();
 
@@ -642,7 +642,7 @@ EXPECTED;
      * @param $smallString
      * @dataProvider dataMinimumWidth
      */
-    public function testMinimumWidth($smallString)
+    public function testMinimumWidth($smallString): void
     {
         $bigString = 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX';
 
@@ -669,7 +669,7 @@ EXPECTED;
         ];
     }
 
-    public function testTableWithAnsiFormat()
+    public function testTableWithAnsiFormat(): void
     {
         $table = new Table();
 
diff --git a/tests/framework/data/ActiveDataFilterTest.php b/tests/framework/data/ActiveDataFilterTest.php
index f710d5b080..57b96a6ab6 100644
--- a/tests/framework/data/ActiveDataFilterTest.php
+++ b/tests/framework/data/ActiveDataFilterTest.php
@@ -167,7 +167,7 @@ class ActiveDataFilterTest extends TestCase
      * @param array $filter
      * @param array $expectedResult
      */
-    public function testBuild($filter, $expectedResult)
+    public function testBuild($filter, $expectedResult): void
     {
         $builder = new ActiveDataFilter();
         $searchModel = (new DynamicModel(['name' => null, 'number' => null, 'price' => null, 'tags' => null]))
@@ -186,7 +186,7 @@ class ActiveDataFilterTest extends TestCase
     /**
      * @depends testBuild
      */
-    public function testBuildCallback()
+    public function testBuildCallback(): void
     {
         $builder = new ActiveDataFilter();
         $searchModel = (new DynamicModel(['name' => null]))
diff --git a/tests/framework/data/ActiveDataProviderCloningTest.php b/tests/framework/data/ActiveDataProviderCloningTest.php
index ad2f67e685..c40e50ffdc 100644
--- a/tests/framework/data/ActiveDataProviderCloningTest.php
+++ b/tests/framework/data/ActiveDataProviderCloningTest.php
@@ -14,7 +14,7 @@ use yiiunit\TestCase;
 
 class ActiveDataProviderCloningTest extends TestCase
 {
-    public function testClone()
+    public function testClone(): void
     {
         $queryFirst = new Query();
 
diff --git a/tests/framework/data/ActiveDataProviderTest.php b/tests/framework/data/ActiveDataProviderTest.php
index a4018713a2..bff2d173bf 100644
--- a/tests/framework/data/ActiveDataProviderTest.php
+++ b/tests/framework/data/ActiveDataProviderTest.php
@@ -33,7 +33,7 @@ abstract class ActiveDataProviderTest extends DatabaseTestCase
         ActiveRecord::$db = $this->getConnection();
     }
 
-    public function testActiveQuery()
+    public function testActiveQuery(): void
     {
         $provider = new ActiveDataProvider([
             'query' => Order::find()->orderBy('id'),
@@ -55,7 +55,7 @@ abstract class ActiveDataProviderTest extends DatabaseTestCase
         $this->assertCount(2, $orders);
     }
 
-    public function testActiveRelation()
+    public function testActiveRelation(): void
     {
         /** @var Customer $customer */
         $customer = Customer::findOne(2);
@@ -78,7 +78,7 @@ abstract class ActiveDataProviderTest extends DatabaseTestCase
         $this->assertCount(1, $orders);
     }
 
-    public function testActiveRelationVia()
+    public function testActiveRelationVia(): void
     {
         /** @var Order $order */
         $order = Order::findOne(2);
@@ -102,7 +102,7 @@ abstract class ActiveDataProviderTest extends DatabaseTestCase
         $this->assertCount(2, $items);
     }
 
-    public function testActiveRelationViaTable()
+    public function testActiveRelationViaTable(): void
     {
         /** @var Order $order */
         $order = Order::findOne(1);
@@ -124,7 +124,7 @@ abstract class ActiveDataProviderTest extends DatabaseTestCase
         $this->assertCount(1, $items);
     }
 
-    public function testQuery()
+    public function testQuery(): void
     {
         $query = new Query();
         $provider = new ActiveDataProvider([
@@ -148,7 +148,7 @@ abstract class ActiveDataProviderTest extends DatabaseTestCase
         $this->assertCount(2, $orders);
     }
 
-    public function testRefresh()
+    public function testRefresh(): void
     {
         $query = new Query();
         $provider = new ActiveDataProvider([
@@ -163,7 +163,7 @@ abstract class ActiveDataProviderTest extends DatabaseTestCase
         $this->assertCount(2, $provider->getModels());
     }
 
-    public function testPaginationBeforeModels()
+    public function testPaginationBeforeModels(): void
     {
         $query = new Query();
         $provider = new ActiveDataProvider([
@@ -181,7 +181,7 @@ abstract class ActiveDataProviderTest extends DatabaseTestCase
         $this->assertCount(2, $provider->getModels());
     }
 
-    public function testDoesNotPerformQueryWhenHasNoModels()
+    public function testDoesNotPerformQueryWhenHasNoModels(): void
     {
         $query = new UnqueryableQueryMock();
         $provider = new ActiveDataProvider([
diff --git a/tests/framework/data/ArrayDataProviderTest.php b/tests/framework/data/ArrayDataProviderTest.php
index 5347014a07..3c747a5486 100644
--- a/tests/framework/data/ArrayDataProviderTest.php
+++ b/tests/framework/data/ArrayDataProviderTest.php
@@ -22,7 +22,7 @@ class ArrayDataProviderTest extends TestCase
         $this->mockApplication();
     }
 
-    public function testGetModels()
+    public function testGetModels(): void
     {
         $simpleArray = [
             ['name' => 'zero'],
@@ -32,7 +32,7 @@ class ArrayDataProviderTest extends TestCase
         $this->assertEquals($simpleArray, $dataProvider->getModels());
     }
 
-    public function testGetSortedData()
+    public function testGetSortedData(): void
     {
         $simpleArray = [['sortField' => 1], ['sortField' => 0]];
         $dataProvider = new ArrayDataProvider(
@@ -57,7 +57,7 @@ class ArrayDataProviderTest extends TestCase
         $this->assertEquals($sortedArray, $dataProvider->getModels());
     }
 
-    public function testGetSortedDataByInnerArrayField()
+    public function testGetSortedDataByInnerArrayField(): void
     {
         $simpleArray = [
             ['innerArray' => ['sortField' => 1]],
@@ -88,7 +88,7 @@ class ArrayDataProviderTest extends TestCase
         $this->assertEquals($sortedArray, $dataProvider->getModels());
     }
 
-    public function testCaseSensitiveSort()
+    public function testCaseSensitiveSort(): void
     {
         // source data
         $unsortedProjects = [
@@ -157,7 +157,7 @@ class ArrayDataProviderTest extends TestCase
         $this->assertEquals($sortedProjects, $dataProvider->getModels());
     }
 
-    public function testGetKeys()
+    public function testGetKeys(): void
     {
         $pagination = ['pageSize' => 2];
 
@@ -205,7 +205,7 @@ class ArrayDataProviderTest extends TestCase
         $this->assertEquals(['key1', 'key2'], $dataProvider->getKeys());
     }
 
-    public function testSortFlags()
+    public function testSortFlags(): void
     {
         $simpleArray = [['sortField' => 1], ['sortField' => 2], ['sortField' => 11]];
         $dataProvider = new ArrayDataProvider(
diff --git a/tests/framework/data/BaseDataProviderTest.php b/tests/framework/data/BaseDataProviderTest.php
index 774844cc82..06ba88b20d 100644
--- a/tests/framework/data/BaseDataProviderTest.php
+++ b/tests/framework/data/BaseDataProviderTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\data;
 
+use ReflectionClass;
 use yii\data\BaseDataProvider;
 use yiiunit\TestCase;
 
@@ -16,9 +17,9 @@ use yiiunit\TestCase;
  */
 class BaseDataProviderTest extends TestCase
 {
-    public function testGenerateId()
+    public function testGenerateId(): void
     {
-        $rc = new \ReflectionClass(BaseDataProvider::className());
+        $rc = new ReflectionClass(BaseDataProvider::className());
         $rp = $rc->getProperty('counter');
 
         // @link https://wiki.php.net/rfc/deprecations_php_8_5#deprecate_reflectionsetaccessible
diff --git a/tests/framework/data/DataFilterTest.php b/tests/framework/data/DataFilterTest.php
index 4c02569a2b..ba82ca2d98 100644
--- a/tests/framework/data/DataFilterTest.php
+++ b/tests/framework/data/DataFilterTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\data;
 
+use stdClass;
 use yii\base\DynamicModel;
 use yii\data\DataFilter;
 use yiiunit\data\base\Singer;
@@ -27,7 +28,7 @@ class DataFilterTest extends TestCase
 
     // Tests :
 
-    public function testSetupSearchModel()
+    public function testSetupSearchModel(): void
     {
         $builder = new DataFilter();
 
@@ -56,10 +57,10 @@ class DataFilterTest extends TestCase
         $this->assertTrue($model instanceof DynamicModel);
 
         $this->expectException('yii\base\InvalidConfigException');
-        $builder->setSearchModel(new \stdClass());
+        $builder->setSearchModel(new stdClass());
     }
 
-    public function testLoad()
+    public function testLoad(): void
     {
         $filterValue = [
             'name' => 'value',
@@ -263,7 +264,7 @@ class DataFilterTest extends TestCase
      * @param bool $expectedResult
      * @param array $expectedErrors
      */
-    public function testValidate($filter, $expectedResult, $expectedErrors)
+    public function testValidate($filter, $expectedResult, $expectedErrors): void
     {
         $builder = new DataFilter();
         $searchModel = (new DynamicModel([
@@ -420,7 +421,7 @@ class DataFilterTest extends TestCase
      * @param array $filter
      * @param array $expectedResult
      */
-    public function testNormalize($filter, $expectedResult)
+    public function testNormalize($filter, $expectedResult): void
     {
         $builder = new DataFilter();
         $searchModel = (new DynamicModel([
@@ -449,7 +450,7 @@ class DataFilterTest extends TestCase
         $this->assertEquals($expectedResult, $builder->normalize(false));
     }
 
-    public function testNormalizeNonDefaultNull()
+    public function testNormalizeNonDefaultNull(): void
     {
         $builder = new DataFilter();
         $builder->nullValue = 'abcde';
@@ -458,7 +459,7 @@ class DataFilterTest extends TestCase
         $this->assertEquals(['name' => null], $builder->normalize(false));
     }
 
-    public function testSetupErrorMessages()
+    public function testSetupErrorMessages(): void
     {
         $builder = new DataFilter();
         $builder->setErrorMessages([
diff --git a/tests/framework/data/PaginationTest.php b/tests/framework/data/PaginationTest.php
index 9c71cacce1..bc19ce165e 100644
--- a/tests/framework/data/PaginationTest.php
+++ b/tests/framework/data/PaginationTest.php
@@ -79,7 +79,7 @@ class PaginationTest extends TestCase
      * @param array $params
      * @param bool $absolute
      */
-    public function testCreateUrl($page, $pageSize, $expectedUrl, $params, $absolute = false)
+    public function testCreateUrl($page, $pageSize, $expectedUrl, $params, $absolute = false): void
     {
         $pagination = new Pagination();
         $pagination->route = 'item/list';
@@ -90,7 +90,7 @@ class PaginationTest extends TestCase
     /**
      * @depends testCreateUrl
      */
-    public function testForcePageParam()
+    public function testForcePageParam(): void
     {
         $pagination = new Pagination();
         $pagination->route = 'item/list';
@@ -102,7 +102,7 @@ class PaginationTest extends TestCase
         $this->assertEquals('/index.php?r=item%2Flist', $pagination->createUrl(0));
     }
 
-    public function testValidatePage()
+    public function testValidatePage(): void
     {
         $pagination = new Pagination();
         $pagination->validatePage = true;
@@ -139,7 +139,7 @@ class PaginationTest extends TestCase
      * @param int $totalCount
      * @param int $pageCount
      */
-    public function testPageCount($pageSize, $totalCount, $pageCount)
+    public function testPageCount($pageSize, $totalCount, $pageCount): void
     {
         $pagination = new Pagination();
         $pagination->setPageSize($pageSize);
@@ -148,7 +148,7 @@ class PaginationTest extends TestCase
         $this->assertEquals($pageCount, $pagination->getPageCount());
     }
 
-    public function testGetDefaultPage()
+    public function testGetDefaultPage(): void
     {
         $this->assertEquals(0, (new Pagination())->getPage());
     }
@@ -179,7 +179,7 @@ class PaginationTest extends TestCase
      * @param int $totalCount
      * @param int $page
      */
-    public function testSetPage($value, $validate, $totalCount, $page)
+    public function testSetPage($value, $validate, $totalCount, $page): void
     {
         $pagination = new Pagination();
         $pagination->totalCount = $totalCount;
@@ -207,7 +207,7 @@ class PaginationTest extends TestCase
      * @param array|bool $pageSizeLimit
      * @param int $pageSize
      */
-    public function testGetPageSize($pageSizeLimit, $pageSize)
+    public function testGetPageSize($pageSizeLimit, $pageSize): void
     {
         $pagination = new Pagination();
         $pagination->pageSizeLimit = $pageSizeLimit;
@@ -241,7 +241,7 @@ class PaginationTest extends TestCase
      * @param array|false $pageSizeLimit
      * @param int $pageSize
      */
-    public function testSetPageSize($value, $validate, $pageSizeLimit, $pageSize)
+    public function testSetPageSize($value, $validate, $pageSizeLimit, $pageSize): void
     {
         $pagination = new Pagination();
         $pagination->pageSizeLimit = $pageSizeLimit;
@@ -268,7 +268,7 @@ class PaginationTest extends TestCase
      * @param int $page
      * @param int $offset
      */
-    public function testGetOffset($pageSize, $page, $offset)
+    public function testGetOffset($pageSize, $page, $offset): void
     {
         $pagination = new Pagination();
         $pagination->setPageSize($pageSize);
@@ -292,7 +292,7 @@ class PaginationTest extends TestCase
      * @param int $pageSize
      * @param int $limit
      */
-    public function testGetLimit($pageSize, $limit)
+    public function testGetLimit($pageSize, $limit): void
     {
         $pagination = new Pagination();
         $pagination->setPageSize($pageSize);
@@ -390,7 +390,7 @@ class PaginationTest extends TestCase
      * @param string|null $prev
      * @param string|null $next
      */
-    public function testGetLinks($page, $pageSize, $totalCount, $self, $first, $last, $prev, $next)
+    public function testGetLinks($page, $pageSize, $totalCount, $self, $first, $last, $prev, $next): void
     {
         $pagination = new Pagination();
         $pagination->totalCount = $totalCount;
diff --git a/tests/framework/data/SortTest.php b/tests/framework/data/SortTest.php
index 5b0a510f46..dc70179c42 100644
--- a/tests/framework/data/SortTest.php
+++ b/tests/framework/data/SortTest.php
@@ -26,7 +26,7 @@ class SortTest extends TestCase
         $this->mockApplication();
     }
 
-    public function testGetOrders()
+    public function testGetOrders(): void
     {
         $sort = new Sort([
             'attributes' => [
@@ -54,7 +54,7 @@ class SortTest extends TestCase
         $this->assertEquals(SORT_ASC, $orders['age']);
     }
 
-    public function testGetAttributeOrders()
+    public function testGetAttributeOrders(): void
     {
         $sort = new Sort([
             'attributes' => [
@@ -81,7 +81,7 @@ class SortTest extends TestCase
         $this->assertEquals(SORT_ASC, $orders['age']);
     }
 
-    public function testGetAttributeOrder()
+    public function testGetAttributeOrder(): void
     {
         $sort = new Sort([
             'attributes' => [
@@ -102,7 +102,7 @@ class SortTest extends TestCase
         $this->assertNull($sort->getAttributeOrder('xyz'));
     }
 
-    public function testSetAttributeOrders()
+    public function testSetAttributeOrders(): void
     {
         $sort = new Sort([
             'attributes' => [
@@ -138,7 +138,7 @@ class SortTest extends TestCase
         $this->assertEquals($orders, $sort->getAttributeOrders());
     }
 
-    public function testCreateSortParam()
+    public function testCreateSortParam(): void
     {
         $sort = new Sort([
             'attributes' => [
@@ -181,7 +181,7 @@ class SortTest extends TestCase
         $this->assertEquals('age', $sort->createSortParam('name'));
     }
 
-    public function testCreateUrl()
+    public function testCreateUrl(): void
     {
         $manager = new UrlManager([
             'baseUrl' => '/',
@@ -222,7 +222,7 @@ class SortTest extends TestCase
     /**
      * @dataProvider providerForLinkWithParams
      */
-    public function testLinkWithParams($enableMultiSort, $defaultOrder, $link)
+    public function testLinkWithParams($enableMultiSort, $defaultOrder, $link): void
     {
         $this->mockApplication();
         $manager = new UrlManager([
@@ -263,7 +263,7 @@ class SortTest extends TestCase
     /**
      * @dataProvider providerForLinkWithParamsAndPassedButEmptySort
      */
-    public function testLinkWithParamsAndPassedButEmptySort($defaultOrder)
+    public function testLinkWithParamsAndPassedButEmptySort($defaultOrder): void
     {
         $this->mockApplication();
         $manager = new UrlManager([
@@ -310,7 +310,7 @@ class SortTest extends TestCase
     /**
      * @dataProvider providerForLinkWithoutParams
      */
-    public function testLinkWithoutParams($enableMultiSort, $defaultOrder, $link)
+    public function testLinkWithoutParams($enableMultiSort, $defaultOrder, $link): void
     {
         $this->mockApplication();
         $manager = new UrlManager([
@@ -336,7 +336,7 @@ class SortTest extends TestCase
         $this->assertEquals($link, $sort->link('age'));
     }
 
-    public function testParseSortParam()
+    public function testParseSortParam(): void
     {
         $sort = new CustomSort([
             'attributes' => [
@@ -359,7 +359,7 @@ class SortTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/pull/13260
      */
-    public function testGetExpressionOrders()
+    public function testGetExpressionOrders(): void
     {
         $sort = new Sort([
             'attributes' => [
diff --git a/tests/framework/data/SqlDataProviderTest.php b/tests/framework/data/SqlDataProviderTest.php
index 9af783bef8..e997304e64 100644
--- a/tests/framework/data/SqlDataProviderTest.php
+++ b/tests/framework/data/SqlDataProviderTest.php
@@ -18,7 +18,7 @@ class SqlDataProviderTest extends DatabaseTestCase
 {
     protected $driverName = 'sqlite';
 
-    public function testGetModels()
+    public function testGetModels(): void
     {
         $dataProvider = new SqlDataProvider([
             'sql' => 'select * from `customer`',
@@ -27,7 +27,7 @@ class SqlDataProviderTest extends DatabaseTestCase
         $this->assertCount(3, $dataProvider->getModels());
     }
 
-    public function testTotalCount()
+    public function testTotalCount(): void
     {
         $dataProvider = new SqlDataProvider([
             'sql' => 'select * from `customer`',
@@ -36,7 +36,7 @@ class SqlDataProviderTest extends DatabaseTestCase
         $this->assertEquals(3, $dataProvider->getTotalCount());
     }
 
-    public function testTotalCountWithParams()
+    public function testTotalCountWithParams(): void
     {
         $dataProvider = new SqlDataProvider([
             'sql' => 'select * from `customer` where id > :minimum',
@@ -66,7 +66,7 @@ class SqlDataProviderTest extends DatabaseTestCase
      * @dataProvider providerForOrderByColumn
      * @see https://github.com/yiisoft/yii2/issues/18552
      */
-    public function testRemovingOrderBy($column)
+    public function testRemovingOrderBy($column): void
     {
         $dataProvider = new SqlDataProvider([
             'sql' => 'select * from `customer` order by ' . $column . ' desc',
diff --git a/tests/framework/db/ActiveQueryModelConnectionTest.php b/tests/framework/db/ActiveQueryModelConnectionTest.php
index 4adb9d8abb..e8a220c427 100644
--- a/tests/framework/db/ActiveQueryModelConnectionTest.php
+++ b/tests/framework/db/ActiveQueryModelConnectionTest.php
@@ -32,7 +32,7 @@ class ActiveQueryModelConnectionTest extends TestCase
         ActiveRecord::$db = $this->modelConnection;
     }
 
-    private function prepareConnectionMock($connection)
+    private function prepareConnectionMock($connection): void
     {
         $command = $this->getMockBuilder('yii\db\Command')->getMock();
         $command->method('queryOne')->willReturn(false);
@@ -41,7 +41,7 @@ class ActiveQueryModelConnectionTest extends TestCase
         $connection->expects($this->once())->method('getQueryBuilder')->willReturn($builder);
     }
 
-    public function testEnsureModelConnectionForOne()
+    public function testEnsureModelConnectionForOne(): void
     {
         $this->globalConnection->expects($this->never())->method('getQueryBuilder');
         $this->prepareConnectionMock($this->modelConnection);
@@ -50,7 +50,7 @@ class ActiveQueryModelConnectionTest extends TestCase
         $query->one();
     }
 
-    public function testEnsureGlobalConnectionForOne()
+    public function testEnsureGlobalConnectionForOne(): void
     {
         $this->modelConnection->expects($this->never())->method('getQueryBuilder');
         $this->prepareConnectionMock($this->globalConnection);
@@ -59,7 +59,7 @@ class ActiveQueryModelConnectionTest extends TestCase
         $query->one();
     }
 
-    public function testEnsureModelConnectionForAll()
+    public function testEnsureModelConnectionForAll(): void
     {
         $this->globalConnection->expects($this->never())->method('getQueryBuilder');
         $this->prepareConnectionMock($this->modelConnection);
@@ -68,7 +68,7 @@ class ActiveQueryModelConnectionTest extends TestCase
         $query->all();
     }
 
-    public function testEnsureGlobalConnectionForAll()
+    public function testEnsureGlobalConnectionForAll(): void
     {
         $this->modelConnection->expects($this->never())->method('getQueryBuilder');
         $this->prepareConnectionMock($this->globalConnection);
diff --git a/tests/framework/db/ActiveQueryTest.php b/tests/framework/db/ActiveQueryTest.php
index 6fb6b575a9..e7969ad73b 100644
--- a/tests/framework/db/ActiveQueryTest.php
+++ b/tests/framework/db/ActiveQueryTest.php
@@ -31,7 +31,7 @@ abstract class ActiveQueryTest extends DatabaseTestCase
         ActiveRecord::$db = $this->getConnection();
     }
 
-    public function testConstructor()
+    public function testConstructor(): void
     {
         $config = [
             'on' => ['a' => 'b'],
@@ -43,10 +43,10 @@ abstract class ActiveQueryTest extends DatabaseTestCase
         $this->assertEquals($query->joinWith, $config['joinWith']);
     }
 
-    public function testTriggerInitEvent()
+    public function testTriggerInitEvent(): void
     {
         $where = '1==1';
-        $callback = function (\yii\base\Event $event) use ($where) {
+        $callback = function (Event $event) use ($where) {
             $event->sender->where = $where;
         };
         Event::on(ActiveQuery::className(), ActiveQuery::EVENT_INIT, $callback);
@@ -58,7 +58,7 @@ abstract class ActiveQueryTest extends DatabaseTestCase
     /**
      * @todo tests for internal logic of prepare()
      */
-    public function testPrepare()
+    public function testPrepare(): void
     {
         $query = new ActiveQuery(Customer::className());
         $builder = new QueryBuilder(new Connection());
@@ -66,7 +66,7 @@ abstract class ActiveQueryTest extends DatabaseTestCase
         $this->assertInstanceOf('yii\db\Query', $result);
     }
 
-    public function testPopulate_EmptyRows()
+    public function testPopulate_EmptyRows(): void
     {
         $query = new ActiveQuery(Customer::className());
         $rows = [];
@@ -77,7 +77,7 @@ abstract class ActiveQueryTest extends DatabaseTestCase
     /**
      * @todo tests for internal logic of populate()
      */
-    public function testPopulate_FilledRows()
+    public function testPopulate_FilledRows(): void
     {
         $query = new ActiveQuery(Customer::className());
         $rows = $query->all();
@@ -88,7 +88,7 @@ abstract class ActiveQueryTest extends DatabaseTestCase
     /**
      * @todo tests for internal logic of one()
      */
-    public function testOne()
+    public function testOne(): void
     {
         $query = new ActiveQuery(Customer::className());
         $result = $query->one();
@@ -98,7 +98,7 @@ abstract class ActiveQueryTest extends DatabaseTestCase
     /**
      * @todo test internal logic of createCommand()
      */
-    public function testCreateCommand()
+    public function testCreateCommand(): void
     {
         $query = new ActiveQuery(Customer::className());
         $result = $query->createCommand();
@@ -108,7 +108,7 @@ abstract class ActiveQueryTest extends DatabaseTestCase
     /**
      * @todo tests for internal logic of queryScalar()
      */
-    public function testQueryScalar()
+    public function testQueryScalar(): void
     {
         $query = new ActiveQuery(Customer::className());
         $result = $this->invokeMethod($query, 'queryScalar', ['name', null]);
@@ -118,7 +118,7 @@ abstract class ActiveQueryTest extends DatabaseTestCase
     /**
      * @todo tests for internal logic of joinWith()
      */
-    public function testJoinWith()
+    public function testJoinWith(): void
     {
         $query = new ActiveQuery(Customer::className());
         $result = $query->joinWith('profile');
@@ -130,7 +130,7 @@ abstract class ActiveQueryTest extends DatabaseTestCase
     /**
      * @todo tests for internal logic of innerJoinWith()
      */
-    public function testInnerJoinWith()
+    public function testInnerJoinWith(): void
     {
         $query = new ActiveQuery(Customer::className());
         $result = $query->innerJoinWith('profile');
@@ -139,7 +139,7 @@ abstract class ActiveQueryTest extends DatabaseTestCase
         ], $result->joinWith);
     }
 
-    public function testBuildJoinWithRemoveDuplicateJoinByTableName()
+    public function testBuildJoinWithRemoveDuplicateJoinByTableName(): void
     {
         $query = new ActiveQuery(Customer::className());
         $query->innerJoinWith('orders')
@@ -162,14 +162,14 @@ abstract class ActiveQueryTest extends DatabaseTestCase
     /**
      * @todo tests for the regex inside getQueryTableName
      */
-    public function testGetQueryTableName_from_not_set()
+    public function testGetQueryTableName_from_not_set(): void
     {
         $query = new ActiveQuery(Customer::className());
         $result = $this->invokeMethod($query, 'getTableNameAndAlias');
         $this->assertEquals(['customer', 'customer'], $result);
     }
 
-    public function testGetQueryTableName_from_set()
+    public function testGetQueryTableName_from_set(): void
     {
         $options = ['from' => ['alias' => 'customer']];
         $query = new ActiveQuery(Customer::className(), $options);
@@ -177,7 +177,7 @@ abstract class ActiveQueryTest extends DatabaseTestCase
         $this->assertEquals(['customer', 'alias'], $result);
     }
 
-    public function testOnCondition()
+    public function testOnCondition(): void
     {
         $query = new ActiveQuery(Customer::className());
         $on = ['active' => true];
@@ -187,7 +187,7 @@ abstract class ActiveQueryTest extends DatabaseTestCase
         $this->assertEquals($params, $result->params);
     }
 
-    public function testAndOnCondition_on_not_set()
+    public function testAndOnCondition_on_not_set(): void
     {
         $query = new ActiveQuery(Customer::className());
         $on = ['active' => true];
@@ -197,7 +197,7 @@ abstract class ActiveQueryTest extends DatabaseTestCase
         $this->assertEquals($params, $result->params);
     }
 
-    public function testAndOnCondition_on_set()
+    public function testAndOnCondition_on_set(): void
     {
         $onOld = ['active' => true];
         $query = new ActiveQuery(Customer::className());
@@ -210,7 +210,7 @@ abstract class ActiveQueryTest extends DatabaseTestCase
         $this->assertEquals($params, $result->params);
     }
 
-    public function testOrOnCondition_on_not_set()
+    public function testOrOnCondition_on_not_set(): void
     {
         $query = new ActiveQuery(Customer::className());
         $on = ['active' => true];
@@ -220,7 +220,7 @@ abstract class ActiveQueryTest extends DatabaseTestCase
         $this->assertEquals($params, $result->params);
     }
 
-    public function testOrOnCondition_on_set()
+    public function testOrOnCondition_on_set(): void
     {
         $onOld = ['active' => true];
         $query = new ActiveQuery(Customer::className());
@@ -236,7 +236,7 @@ abstract class ActiveQueryTest extends DatabaseTestCase
     /**
      * @todo tests for internal logic of viaTable()
      */
-    public function testViaTable()
+    public function testViaTable(): void
     {
         $query = new ActiveQuery(Customer::className(), ['primaryModel' => new Order()]);
         $result = $query->viaTable(Profile::className(), ['id' => 'item_id']);
@@ -244,7 +244,7 @@ abstract class ActiveQueryTest extends DatabaseTestCase
         $this->assertInstanceOf('yii\db\ActiveQuery', $result->via);
     }
 
-    public function testAlias_not_set()
+    public function testAlias_not_set(): void
     {
         $query = new ActiveQuery(Customer::className());
         $result = $query->alias('alias');
@@ -252,7 +252,7 @@ abstract class ActiveQueryTest extends DatabaseTestCase
         $this->assertEquals(['alias' => 'customer'], $result->from);
     }
 
-    public function testAlias_yet_set()
+    public function testAlias_yet_set(): void
     {
         $aliasOld = ['old'];
         $query = new ActiveQuery(Customer::className());
@@ -267,7 +267,7 @@ abstract class ActiveQueryTest extends DatabaseTestCase
         return new ActiveQuery(null);
     }
 
-    public function testGetTableNames_notFilledFrom()
+    public function testGetTableNames_notFilledFrom(): void
     {
         $query = new ActiveQuery(Profile::className());
 
@@ -278,7 +278,7 @@ abstract class ActiveQueryTest extends DatabaseTestCase
         ], $tables);
     }
 
-    public function testGetTableNames_wontFillFrom()
+    public function testGetTableNames_wontFillFrom(): void
     {
         $query = new ActiveQuery(Profile::className());
         $this->assertEquals($query->from, null);
@@ -292,7 +292,7 @@ abstract class ActiveQueryTest extends DatabaseTestCase
      * Issue:     Plan     1 -- * Account * -- * User
      * Our Tests: Category 1 -- * Item    * -- * Order
      */
-    public function testDeeplyNestedTableRelationWith()
+    public function testDeeplyNestedTableRelationWith(): void
     {
         /** @var Category $category */
         $categories = Category::find()->with('orders')->indexBy('id')->all();
diff --git a/tests/framework/db/ActiveRecordTest.php b/tests/framework/db/ActiveRecordTest.php
index e8107d9ad2..173aae9b47 100644
--- a/tests/framework/db/ActiveRecordTest.php
+++ b/tests/framework/db/ActiveRecordTest.php
@@ -8,6 +8,9 @@
 
 namespace yiiunit\framework\db;
 
+use Yii;
+use yii\base\InvalidArgumentException;
+use yii\base\InvalidConfigException;
 use yii\db\ActiveQuery;
 use yii\db\ActiveRecordInterface;
 use yii\db\Query;
@@ -108,7 +111,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         return OrderItemWithNullFK::className();
     }
 
-    public function testCustomColumns()
+    public function testCustomColumns(): void
     {
         // find custom column
         if ($this->driverName === 'oci') {
@@ -122,7 +125,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         $this->assertEquals(4, $customer->status2);
     }
 
-    public function testStatisticalFind()
+    public function testStatisticalFind(): void
     {
         // find count, sum, average, min, max, scalar
         $this->assertEquals(3, Customer::find()->count());
@@ -134,14 +137,14 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         $this->assertEquals(3, Customer::find()->select('COUNT(*)')->scalar());
     }
 
-    public function testFindScalar()
+    public function testFindScalar(): void
     {
         // query scalar
         $customerName = Customer::find()->where(['[[id]]' => 2])->select('[[name]]')->scalar();
         $this->assertEquals('user2', $customerName);
     }
 
-    public function testFindExists()
+    public function testFindExists(): void
     {
         $this->assertTrue(Customer::find()->where(['[[id]]' => 2])->exists());
         $this->assertFalse(Customer::find()->where(['[[id]]' => 42])->exists());
@@ -149,14 +152,14 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         $this->assertFalse(Customer::find()->where(['[[id]]' => 42])->select('[[name]]')->exists());
     }
 
-    public function testFindColumn()
+    public function testFindColumn(): void
     {
         /** @var TestCase|ActiveRecordTestTrait $this */
         $this->assertEquals(['user1', 'user2', 'user3'], Customer::find()->select('[[name]]')->column());
         $this->assertEquals(['user3', 'user2', 'user1'], Customer::find()->orderBy(['[[name]]' => SORT_DESC])->select('[[name]]')->column());
     }
 
-    public function testFindBySql()
+    public function testFindBySql(): void
     {
         // find one
         $customer = Customer::findBySql('SELECT * FROM {{customer}} ORDER BY [[id]] DESC')->one();
@@ -178,7 +181,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
      *
      * @see https://github.com/yiisoft/yii2/issues/8593
      */
-    public function testCountWithFindBySql()
+    public function testCountWithFindBySql(): void
     {
         $query = Customer::findBySql('SELECT * FROM {{customer}}');
         $this->assertEquals(3, $query->count());
@@ -186,7 +189,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         $this->assertEquals(1, $query->count());
     }
 
-    public function testFindLazyViaTable()
+    public function testFindLazyViaTable(): void
     {
         /** @var Order $order */
         $order = Order::findOne(1);
@@ -203,7 +206,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         $this->assertIsArray($order);
     }
 
-    public function testFindEagerViaTable()
+    public function testFindEagerViaTable(): void
     {
         $orders = Order::find()->with('books')->orderBy('id')->all();
         $this->assertCount(3, $orders);
@@ -237,7 +240,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
     }
 
     // deeply nested table relation
-    public function testDeeplyNestedTableRelation()
+    public function testDeeplyNestedTableRelation(): void
     {
         /** @var Customer $customer */
         $customer = Customer::findOne(1);
@@ -258,7 +261,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
      * Issue:     Plan     1 -- * Account * -- * User
      * Our Tests: Category 1 -- * Item    * -- * Order
      */
-    public function testDeeplyNestedTableRelation2()
+    public function testDeeplyNestedTableRelation2(): void
     {
         /** @var Category $category */
         $category = Category::findOne(1);
@@ -279,7 +282,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         $this->assertEquals(2, $orders[0]->id);
     }
 
-    public function testStoreNull()
+    public function testStoreNull(): void
     {
         $record = new NullValues();
         $this->assertNull($record->var1);
@@ -327,7 +330,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         $this->assertEquals('', $record->stringcol);
     }
 
-    public function testStoreEmpty()
+    public function testStoreEmpty(): void
     {
         $record = new NullValues();
 
@@ -345,7 +348,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         $this->assertSame($record->var2, $record->var3);
     }
 
-    public function testIsPrimaryKey()
+    public function testIsPrimaryKey(): void
     {
         $this->assertFalse(Customer::isPrimaryKey([]));
         $this->assertTrue(Customer::isPrimaryKey(['id']));
@@ -362,7 +365,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         $this->assertFalse(OrderItem::isPrimaryKey(['order_id', 'item_id', 'quantity']));
     }
 
-    public function testJoinWith()
+    public function testJoinWith(): void
     {
         // left join and eager loading
         $orders = Order::find()->joinWith('customer')->orderBy('customer.id DESC, order.id')->all();
@@ -567,7 +570,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
     /**
      * @depends testJoinWith
      */
-    public function testJoinWithDuplicateSimple()
+    public function testJoinWithDuplicateSimple(): void
     {
         // left join and eager loading
         $orders = Order::find()
@@ -587,7 +590,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
     /**
      * @depends testJoinWith
      */
-    public function testJoinWithDuplicateCallbackFiltering()
+    public function testJoinWithDuplicateCallbackFiltering(): void
     {
         // inner join filtering and eager loading
         $orders = Order::find()
@@ -607,7 +610,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
     /**
      * @depends testJoinWith
      */
-    public function testJoinWithDuplicateCallbackFilteringConditionsOnPrimary()
+    public function testJoinWithDuplicateCallbackFilteringConditionsOnPrimary(): void
     {
         // inner join filtering, eager loading, conditions on both primary and relation
         $orders = Order::find()
@@ -625,7 +628,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
     /**
      * @depends testJoinWith
      */
-    public function testJoinWithDuplicateWithSubRelation()
+    public function testJoinWithDuplicateWithSubRelation(): void
     {
         // join with sub-relation
         $orders = Order::find()
@@ -646,7 +649,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
     /**
      * @depends testJoinWith
      */
-    public function testJoinWithDuplicateTableAlias1()
+    public function testJoinWithDuplicateTableAlias1(): void
     {
         // join with table alias
         $orders = Order::find()
@@ -668,7 +671,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
     /**
      * @depends testJoinWith
      */
-    public function testJoinWithDuplicateTableAlias2()
+    public function testJoinWithDuplicateTableAlias2(): void
     {
         // join with table alias
         $orders = Order::find()
@@ -688,7 +691,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
     /**
      * @depends testJoinWith
      */
-    public function testJoinWithDuplicateTableAliasSubRelation()
+    public function testJoinWithDuplicateTableAliasSubRelation(): void
     {
         // join with table alias sub-relation
         $orders = Order::find()
@@ -713,7 +716,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
     /**
      * @depends testJoinWith
      */
-    public function testJoinWithDuplicateSubRelationCalledInsideClosure()
+    public function testJoinWithDuplicateSubRelationCalledInsideClosure(): void
     {
         // join with sub-relation called inside Closure
         $orders = Order::find()
@@ -741,7 +744,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
     /**
      * @depends testJoinWith
      */
-    public function testJoinWithAndScope()
+    public function testJoinWithAndScope(): void
     {
         // hasOne inner join
         $customers = Customer::find()->active()->innerJoinWith('profile')->orderBy('customer.id')->all();
@@ -777,7 +780,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
      *
      * @see https://github.com/yiisoft/yii2/pull/2650
      */
-    public function testJoinWithVia()
+    public function testJoinWithVia(): void
     {
         Order::getDb()->getQueryBuilder()->separator = "\n";
         $rows = Order::find()->joinWith('itemsInOrder1')->joinWith([
@@ -793,7 +796,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
      *
      * @see https://github.com/yiisoft/yii2/issues/19507
      */
-    public function testJoinWithEager()
+    public function testJoinWithEager(): void
     {
         $eagerCustomers = Customer::find()->joinWith(['items'])->all();
         $eagerItemsCount = 0;
@@ -825,7 +828,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
      * @dataProvider aliasMethodProvider
      * @param string $aliasMethod whether alias is specified explicitly or using the query syntax {{@tablename}}
      */
-    public function testJoinWithAlias($aliasMethod)
+    public function testJoinWithAlias($aliasMethod): void
     {
         // left join and eager loading
         /** @var ActiveQuery $query */
@@ -1009,7 +1012,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         $this->assertEquals(2, $orders[0]->items[0]->category->id);
     }
 
-    public function testJoinWithSameTable()
+    public function testJoinWithSameTable(): void
     {
         // join with the same table but different aliases
         // alias is defined in the relation definition
@@ -1097,7 +1100,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
      * @see https://github.com/yiisoft/yii2/issues/10201
      * @see https://github.com/yiisoft/yii2/issues/9047
      */
-    public function testFindCompositeRelationWithJoin()
+    public function testFindCompositeRelationWithJoin(): void
     {
         /** @var OrderItem $orderItem */
         $orderItem = OrderItem::findOne([1, 1]);
@@ -1109,7 +1112,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         $this->assertInstanceOf('yiiunit\data\ar\OrderItem', $orderItemWithJoin);
     }
 
-    public function testFindSimpleRelationWithJoin()
+    public function testFindSimpleRelationWithJoin(): void
     {
         /** @var Order $order */
         $order = Order::findOne(1);
@@ -1143,7 +1146,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
      * @param string $orderTableName
      * @param string $orderItemTableName
      */
-    public function testRelationWhereParams($orderTableName, $orderItemTableName)
+    public function testRelationWhereParams($orderTableName, $orderItemTableName): void
     {
         Order::$tableName = $orderTableName;
         OrderItem::$tableName = $orderItemTableName;
@@ -1163,7 +1166,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         OrderItem::$tableName = null;
     }
 
-    public function testOutdatedRelationsAreResetForNewRecords()
+    public function testOutdatedRelationsAreResetForNewRecords(): void
     {
         $orderItem = new OrderItem();
         $orderItem->order_id = 1;
@@ -1184,7 +1187,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         $this->assertEquals(2, $orderItem->item->id);
     }
 
-    public function testOutdatedRelationsAreResetForExistingRecords()
+    public function testOutdatedRelationsAreResetForExistingRecords(): void
     {
         $orderItem = OrderItem::findOne(1);
         $this->assertEquals(1, $orderItem->order->id);
@@ -1203,7 +1206,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         $this->assertEquals(1, $orderItem->item->id);
     }
 
-    public function testOutdatedCompositeKeyRelationsAreReset()
+    public function testOutdatedCompositeKeyRelationsAreReset(): void
     {
         $dossier = Dossier::findOne([
             'department_id' => 1,
@@ -1231,7 +1234,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         $this->assertEquals('Will Smith', $dossier->employee->fullName);
     }
 
-    public function testOutdatedViaTableRelationsAreReset()
+    public function testOutdatedViaTableRelationsAreReset(): void
     {
         $order = Order::findOne(1);
         $orderItemIds = ArrayHelper::getColumn($order->items, 'id');
@@ -1254,7 +1257,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         $this->assertSame([2], $orderItemIds);
     }
 
-    public function testAlias()
+    public function testAlias(): void
     {
         $query = Order::find();
         $this->assertNull($query->from);
@@ -1275,7 +1278,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         ], $query->from);
     }
 
-    public function testInverseOf()
+    public function testInverseOf(): void
     {
         // eager loading: find one and all
         $customer = Customer::find()->with('orders2')->where(['id' => 1])->one();
@@ -1330,7 +1333,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         $this->assertSame($orders[1]['customer2']['orders2'][1]['id'], $orders[1]['id']);
     }
 
-    public function testInverseOfDynamic()
+    public function testInverseOfDynamic(): void
     {
         $customer = Customer::findOne(1);
 
@@ -1356,7 +1359,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         $this->assertEquals($customer['id'], $orders2['customer2']['id']);
     }
 
-    public function testDefaultValues()
+    public function testDefaultValues(): void
     {
         $model = new Type();
         $model->loadDefaultValues();
@@ -1388,7 +1391,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         $this->assertEquals(['int_col2' => 1], $model->toArray());
     }
 
-    public function testUnlinkAllViaTable()
+    public function testUnlinkAllViaTable(): void
     {
         /** @var ActiveRecordInterface $orderClass */
         $orderClass = $this->getOrderClass();
@@ -1422,7 +1425,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         $this->assertEquals(5, $itemClass::find()->count());
     }
 
-    public function testCastValues()
+    public function testCastValues(): void
     {
         $model = new Type();
         $model->int_col = 123;
@@ -1451,7 +1454,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         $this->assertSame(false, $model->bool_col2);
     }
 
-    public function testIssues()
+    public function testIssues(): void
     {
         // https://github.com/yiisoft/yii2/issues/4938
         $category = Category::findOne(2);
@@ -1488,7 +1491,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         $this->assertEquals(1, $model->status);
     }
 
-    public function testPopulateRecordCallWhenQueryingOnParentClass()
+    public function testPopulateRecordCallWhenQueryingOnParentClass(): void
     {
         (new Cat())->save(false);
         (new Dog())->save(false);
@@ -1500,14 +1503,14 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         $this->assertEquals('meow', $animal->getDoes());
     }
 
-    public function testSaveEmpty()
+    public function testSaveEmpty(): void
     {
         $record = new NullValues();
         $this->assertTrue($record->save(false));
         $this->assertEquals(1, $record->id);
     }
 
-    public function testOptimisticLock()
+    public function testOptimisticLock(): void
     {
         /** @var Document $record */
         $record = Document::findOne(1);
@@ -1522,7 +1525,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         $record->save(false);
     }
 
-    public function testPopulateWithoutPk()
+    public function testPopulateWithoutPk(): void
     {
         // tests with single pk asArray
         $aggregation = Customer::find()
@@ -1632,7 +1635,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/9006
      */
-    public function testBit()
+    public function testBit(): void
     {
         $falseBit = BitValues::findOne(1);
         $this->assertEquals(false, $falseBit->val);
@@ -1641,7 +1644,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         $this->assertEquals(true, $trueBit->val);
     }
 
-    public function testLinkWhenRelationIsIndexed2()
+    public function testLinkWhenRelationIsIndexed2(): void
     {
         $order = Order::find()
             ->with('orderItems2')
@@ -1657,7 +1660,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         $this->assertTrue(isset($order->orderItems2['3']));
     }
 
-    public function testLinkWhenRelationIsIndexed3()
+    public function testLinkWhenRelationIsIndexed3(): void
     {
         $order = Order::find()
             ->with('orderItems3')
@@ -1673,7 +1676,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         $this->assertTrue(isset($order->orderItems3['1_3']));
     }
 
-    public function testUpdateAttributes()
+    public function testUpdateAttributes(): void
     {
         $order = Order::findOne(1);
         $newTotal = 978;
@@ -1691,7 +1694,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         $this->assertEquals($newTotal, $newOrder->total);
     }
 
-    public function testEmulateExecution()
+    public function testEmulateExecution(): void
     {
         $this->assertGreaterThan(0, Customer::find()->count());
 
@@ -1751,7 +1754,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/12213
      */
-    public function testUnlinkAllOnCondition()
+    public function testUnlinkAllOnCondition(): void
     {
         /** @var Category $categoryClass */
         $categoryClass = $this->getCategoryClass();
@@ -1782,7 +1785,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/12213
      */
-    public function testUnlinkAllOnConditionViaTable()
+    public function testUnlinkAllOnConditionViaTable(): void
     {
         /** @var Order $orderClass */
         $orderClass = $this->getOrderClass();
@@ -1812,7 +1815,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
     /**
      * https://github.com/yiisoft/yii2/pull/13891
      */
-    public function testIndexByAfterLoadingRelations()
+    public function testIndexByAfterLoadingRelations(): void
     {
         $orderClass = $this->getOrderClass();
 
@@ -1832,7 +1835,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
     /**
      * Verify that {{}} are not going to be replaced in parameters.
      */
-    public function testNoTablenameReplacement()
+    public function testNoTablenameReplacement(): void
     {
         /** @var Customer $customer */
         $class = $this->getCustomerClass();
@@ -1859,7 +1862,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
      *
      * @see https://github.com/yiisoft/yii2/issues/13757
      */
-    public function testAmbiguousColumnFindOne()
+    public function testAmbiguousColumnFindOne(): void
     {
         CustomerQuery::$joinWithProfile = true;
         $model = Customer::findOne(1);
@@ -1867,7 +1870,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         CustomerQuery::$joinWithProfile = false;
     }
 
-    public function testFindOneByColumnName()
+    public function testFindOneByColumnName(): void
     {
         $model = Customer::findOne(['id' => 1]);
         $this->assertEquals(1, $model->id);
@@ -1882,12 +1885,12 @@ abstract class ActiveRecordTest extends DatabaseTestCase
      * @dataProvider filterTableNamesFromAliasesProvider
      * @param $fromParams
      * @param $expectedAliases
-     * @throws \yii\base\InvalidConfigException
+     * @throws InvalidConfigException
      */
-    public function testFilterTableNamesFromAliases($fromParams, $expectedAliases)
+    public function testFilterTableNamesFromAliases($fromParams, $expectedAliases): void
     {
         $query = Customer::find()->from($fromParams);
-        $aliases = $this->invokeMethod(\Yii::createObject(Customer::className()), 'filterValidAliases', [$query]);
+        $aliases = $this->invokeMethod(Yii::createObject(Customer::className()), 'filterValidAliases', [$query]);
 
         $this->assertEquals($expectedAliases, $aliases);
     }
@@ -1926,10 +1929,10 @@ abstract class ActiveRecordTest extends DatabaseTestCase
     /**
      * @dataProvider legalValuesForFindByCondition
      */
-    public function testLegalValuesForFindByCondition($modelClassName, $validFilter)
+    public function testLegalValuesForFindByCondition($modelClassName, $validFilter): void
     {
         /** @var Query $query */
-        $query = $this->invokeMethod(\Yii::createObject($modelClassName), 'findByCondition', [$validFilter]);
+        $query = $this->invokeMethod(Yii::createObject($modelClassName), 'findByCondition', [$validFilter]);
         Customer::getDb()->queryBuilder->build($query);
 
         $this->assertTrue(true);
@@ -1967,12 +1970,12 @@ abstract class ActiveRecordTest extends DatabaseTestCase
     /**
      * @dataProvider illegalValuesForFindByCondition
      */
-    public function testValueEscapingInFindByCondition($modelClassName, $filterWithInjection)
+    public function testValueEscapingInFindByCondition($modelClassName, $filterWithInjection): void
     {
-        $this->expectException(\yii\base\InvalidArgumentException::class);
+        $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessageMatches('/^Key "(.+)?" is not a column name and can not be used as a filter$/');
         /** @var Query $query */
-        $query = $this->invokeMethod(\Yii::createObject($modelClassName), 'findByCondition', $filterWithInjection);
+        $query = $this->invokeMethod(Yii::createObject($modelClassName), 'findByCondition', $filterWithInjection);
         Customer::getDb()->queryBuilder->build($query);
     }
 
@@ -1981,7 +1984,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
      *
      * @see https://github.com/yiisoft/yii2/issues/13859
      */
-    public function testAmbiguousColumnIndexBy()
+    public function testAmbiguousColumnIndexBy(): void
     {
         switch ($this->driverName) {
             case 'pgsql':
@@ -2010,7 +2013,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
      *
      * @depends testJoinWith
      */
-    public function testFindWithConstructors()
+    public function testFindWithConstructors(): void
     {
         /** @var OrderWithConstructor[] $orders */
         $orders = OrderWithConstructor::find()
@@ -2055,15 +2058,15 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         $this->assertCount(3, $orders);
     }
 
-    public function testCustomARRelation()
+    public function testCustomARRelation(): void
     {
         $orderItem = OrderItem::findOne(1);
         $this->assertInstanceOf(Order::className(), $orderItem->custom);
     }
 
-    public function testRefresh_querySetAlias_findRecord()
+    public function testRefresh_querySetAlias_findRecord(): void
     {
-        $customer = new \yiiunit\data\ar\CustomerWithAlias();
+        $customer = new CustomerWithAlias();
         $customer->id = 1;
 
         $customer->refresh();
@@ -2071,7 +2074,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         $this->assertEquals(1, $customer->id);
     }
 
-    public function testResetNotSavedRelation()
+    public function testResetNotSavedRelation(): void
     {
         $order = new Order();
         $order->customer_id = 1;
@@ -2085,7 +2088,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         $this->assertEquals(1, sizeof($order->orderItems));
     }
 
-    public function testIssetThrowable()
+    public function testIssetThrowable(): void
     {
         $cat = new Cat();
         $this->assertFalse(isset($cat->throwable));
@@ -2094,7 +2097,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/15482
      */
-    public function testEagerLoadingUsingStringIdentifiers()
+    public function testEagerLoadingUsingStringIdentifiers(): void
     {
         if (!in_array($this->driverName, ['mysql', 'pgsql', 'sqlite'])) {
             $this->markTestSkipped('This test has fixtures only for databases MySQL, PostgreSQL and SQLite.');
@@ -2118,7 +2121,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/16492
      */
-    public function testEagerLoadingWithTypeCastedCompositeIdentifier()
+    public function testEagerLoadingWithTypeCastedCompositeIdentifier(): void
     {
         $aggregation = Order::find()->joinWith('quantityOrderItems', true)->all();
         foreach ($aggregation as $item) {
@@ -2142,7 +2145,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
      * @dataProvider providerForUnlinkDelete
      * @see https://github.com/yiisoft/yii2/issues/17174
      */
-    public function testUnlinkWithViaOnCondition($delete, $count)
+    public function testUnlinkWithViaOnCondition($delete, $count): void
     {
         /** @var ActiveRecordInterface $orderClass */
         $orderClass = $this->getOrderClass();
@@ -2167,7 +2170,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         ]));
     }
 
-    public function testVirtualRelation()
+    public function testVirtualRelation(): void
     {
         /** @var ActiveRecordInterface $orderClass */
         $orderClass = $this->getOrderClass();
@@ -2202,7 +2205,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
      * @dataProvider labelTestModelProvider
      * @param \yii\db\ActiveRecord $model
      */
-    public function testGetAttributeLabel($model)
+    public function testGetAttributeLabel($model): void
     {
         $this->assertEquals('model3.attr1 from model2', $model->getAttributeLabel('model2.model3.attr1'));
         $this->assertEquals('attr2 from model3', $model->getAttributeLabel('model2.model3.attr2'));
@@ -2211,7 +2214,7 @@ abstract class ActiveRecordTest extends DatabaseTestCase
         $this->assertEquals($model->generateAttributeLabel($attr), $model->getAttributeLabel($attr));
     }
 
-    public function testLoadRelations()
+    public function testLoadRelations(): void
     {
         // Test eager loading relations for multiple primary models using loadRelationsFor().
         /** @var Customer[] $customers */
diff --git a/tests/framework/db/BatchQueryResultTest.php b/tests/framework/db/BatchQueryResultTest.php
index 6415c7afa7..22321b987b 100644
--- a/tests/framework/db/BatchQueryResultTest.php
+++ b/tests/framework/db/BatchQueryResultTest.php
@@ -21,7 +21,7 @@ abstract class BatchQueryResultTest extends DatabaseTestCase
         ActiveRecord::$db = $this->getConnection();
     }
 
-    public function testQuery()
+    public function testQuery(): void
     {
         $db = $this->getConnection();
 
@@ -86,7 +86,7 @@ abstract class BatchQueryResultTest extends DatabaseTestCase
         $this->assertEquals('address3', $allRows['user3']['address']);
     }
 
-    public function testActiveQuery()
+    public function testActiveQuery(): void
     {
         $db = $this->getConnection();
 
@@ -109,7 +109,7 @@ abstract class BatchQueryResultTest extends DatabaseTestCase
         $this->assertCount(0, $customers[2]->orders);
     }
 
-    public function testBatchWithoutDbParameter()
+    public function testBatchWithoutDbParameter(): void
     {
         $query = Customer::find()->orderBy('id')->limit(3);
         $customers = $this->getAllRowsFromBatch($query->batch(2));
@@ -119,7 +119,7 @@ abstract class BatchQueryResultTest extends DatabaseTestCase
         $this->assertEquals('user3', $customers[2]->name);
     }
 
-    public function testBatchWithIndexBy()
+    public function testBatchWithIndexBy(): void
     {
         $query = Customer::find()->orderBy('id')->limit(3)->indexBy('id');
         $customers = $this->getAllRowsFromBatch($query->batch(2));
diff --git a/tests/framework/db/ColumnSchemaBuilderTest.php b/tests/framework/db/ColumnSchemaBuilderTest.php
index 85bfd07369..28b151cc22 100644
--- a/tests/framework/db/ColumnSchemaBuilderTest.php
+++ b/tests/framework/db/ColumnSchemaBuilderTest.php
@@ -55,7 +55,7 @@ abstract class ColumnSchemaBuilderTest extends DatabaseTestCase
      * @param int|null $length
      * @param mixed $calls
      */
-    public function testCustomTypes($expected, $type, $length, $calls)
+    public function testCustomTypes($expected, $type, $length, $calls): void
     {
         $this->checkBuildString($expected, $type, $length, $calls);
     }
@@ -66,7 +66,7 @@ abstract class ColumnSchemaBuilderTest extends DatabaseTestCase
      * @param int|null $length
      * @param array $calls
      */
-    public function checkBuildString($expected, $type, $length, $calls)
+    public function checkBuildString($expected, $type, $length, $calls): void
     {
         $builder = $this->getColumnSchemaBuilder($type, $length);
         foreach ($calls as $call) {
diff --git a/tests/framework/db/CommandTest.php b/tests/framework/db/CommandTest.php
index 8cb4ce737a..a2254031b2 100644
--- a/tests/framework/db/CommandTest.php
+++ b/tests/framework/db/CommandTest.php
@@ -8,6 +8,12 @@
 
 namespace yiiunit\framework\db;
 
+use PDO;
+use Throwable;
+use yii\base\InvalidArgumentException;
+use yiiunit\framework\db\enums\Status;
+use yiiunit\framework\db\enums\StatusTypeString;
+use yiiunit\framework\db\enums\StatusTypeInt;
 use ArrayObject;
 use yii\caching\ArrayCache;
 use yii\db\Connection;
@@ -21,7 +27,7 @@ abstract class CommandTest extends DatabaseTestCase
 {
     protected $upsertTestCharCast = 'CAST([[address]] AS VARCHAR(255))';
 
-    public function testConstruct()
+    public function testConstruct(): void
     {
         $db = $this->getConnection(false);
 
@@ -35,7 +41,7 @@ abstract class CommandTest extends DatabaseTestCase
         $this->assertEquals($sql, $command->sql);
     }
 
-    public function testGetSetSql()
+    public function testGetSetSql(): void
     {
         $db = $this->getConnection(false);
 
@@ -48,7 +54,7 @@ abstract class CommandTest extends DatabaseTestCase
         $this->assertEquals($sql2, $command->sql);
     }
 
-    public function testAutoQuoting()
+    public function testAutoQuoting(): void
     {
         $db = $this->getConnection(false);
 
@@ -57,7 +63,7 @@ abstract class CommandTest extends DatabaseTestCase
         $this->assertEquals('SELECT `id`, `t`.`name` FROM `customer` t', $command->sql);
     }
 
-    public function testPrepareCancel()
+    public function testPrepareCancel(): void
     {
         $db = $this->getConnection(false);
 
@@ -69,7 +75,7 @@ abstract class CommandTest extends DatabaseTestCase
         $this->assertNull($command->pdoStatement);
     }
 
-    public function testExecute()
+    public function testExecute(): void
     {
         $db = $this->getConnection();
 
@@ -86,7 +92,7 @@ abstract class CommandTest extends DatabaseTestCase
         $command->execute();
     }
 
-    public function testQuery()
+    public function testQuery(): void
     {
         $db = $this->getConnection();
 
@@ -147,7 +153,7 @@ abstract class CommandTest extends DatabaseTestCase
         $command->query();
     }
 
-    public function testBindParamValue()
+    public function testBindParamValue(): void
     {
         if (\defined('HHVM_VERSION') && $this->driverName === 'pgsql') {
             $this->markTestSkipped('HHVMs PgSQL implementation has some specific behavior that breaks some parts of this test.');
@@ -178,7 +184,7 @@ SQL;
         $command = $db->createCommand($sql);
         $intCol = 123;
         $charCol = str_repeat('abc', 33) . 'x'; // a 100 char string
-        $command->bindParam(':int_col', $intCol, \PDO::PARAM_INT);
+        $command->bindParam(':int_col', $intCol, PDO::PARAM_INT);
         $command->bindParam(':char_col', $charCol);
         if ($this->driverName === 'oci') {
             // can't bind floats without support from a custom PDO driver
@@ -189,10 +195,10 @@ SQL;
             // You can create a table with a column of datatype CHAR(1) and store either “Y” or “N” in that column
             // to indicate TRUE or FALSE.
             $boolCol = '0';
-            $command->bindParam(':float_col', $floatCol, \PDO::PARAM_INT);
-            $command->bindParam(':numeric_col', $numericCol, \PDO::PARAM_INT);
+            $command->bindParam(':float_col', $floatCol, PDO::PARAM_INT);
+            $command->bindParam(':numeric_col', $numericCol, PDO::PARAM_INT);
             $command->bindParam(':blob_col', $blobCol);
-            $command->bindParam(':bool_col', $boolCol, \PDO::PARAM_BOOL);
+            $command->bindParam(':bool_col', $boolCol, PDO::PARAM_BOOL);
         } else {
             $floatCol = 1.230;
             $numericCol = '1.23';
@@ -201,7 +207,7 @@ SQL;
             $command->bindParam(':float_col', $floatCol);
             $command->bindParam(':numeric_col', $numericCol);
             $command->bindParam(':blob_col', $blobCol);
-            $command->bindParam(':bool_col', $boolCol, \PDO::PARAM_BOOL);
+            $command->bindParam(':bool_col', $boolCol, PDO::PARAM_BOOL);
         }
         $this->assertEquals(1, $command->execute());
 
@@ -253,7 +259,7 @@ SQL;
      * @dataProvider paramsNonWhereProvider
      * @param string $sql
      */
-    public function testBindParamsNonWhere($sql)
+    public function testBindParamsNonWhere($sql): void
     {
         $db = $this->getConnection();
 
@@ -267,7 +273,7 @@ SQL;
         $this->assertEquals('Params', $command->queryScalar());
     }
 
-    public function testFetchMode()
+    public function testFetchMode(): void
     {
         $db = $this->getConnection();
 
@@ -280,18 +286,18 @@ SQL;
         // FETCH_OBJ, customized via fetchMode property
         $sql = 'SELECT * FROM {{customer}}';
         $command = $db->createCommand($sql);
-        $command->fetchMode = \PDO::FETCH_OBJ;
+        $command->fetchMode = PDO::FETCH_OBJ;
         $result = $command->queryOne();
         $this->assertIsObject($result);
 
         // FETCH_NUM, customized in query method
         $sql = 'SELECT * FROM {{customer}}';
         $command = $db->createCommand($sql);
-        $result = $command->queryOne([], \PDO::FETCH_NUM);
+        $result = $command->queryOne([], PDO::FETCH_NUM);
         $this->assertTrue(\is_array($result) && isset($result[0]));
     }
 
-    public function testBatchInsert()
+    public function testBatchInsert(): void
     {
         $command = $this->getConnection()->createCommand();
         $command->batchInsert(
@@ -314,7 +320,7 @@ SQL;
         $this->assertEquals(0, $command->execute());
     }
 
-    public function testBatchInsertWithYield()
+    public function testBatchInsertWithYield(): void
     {
         include __DIR__ . '/testBatchInsertWithYield.php';
     }
@@ -326,7 +332,7 @@ SQL;
      *
      * https://github.com/yiisoft/yii2/issues/6526
      */
-    public function testBatchInsertDataTypesLocale()
+    public function testBatchInsertDataTypesLocale(): void
     {
         $locale = setlocale(LC_NUMERIC, 0);
         if (false === $locale) {
@@ -367,7 +373,7 @@ SQL;
         } catch (\Exception $e) {
             setlocale(LC_NUMERIC, $locale);
             throw $e;
-        } catch (\Throwable $e) {
+        } catch (Throwable $e) {
             setlocale(LC_NUMERIC, $locale);
             throw $e;
         }
@@ -426,7 +432,7 @@ SQL;
      * @param mixed $expected
      * @param array $expectedParams
      */
-    public function testBatchInsertSQL($table, $columns, $values, $expected, array $expectedParams = [])
+    public function testBatchInsertSQL($table, $columns, $values, $expected, array $expectedParams = []): void
     {
         $command = $this->getConnection()->createCommand();
         $command->batchInsert($table, $columns, $values);
@@ -435,7 +441,7 @@ SQL;
         $this->assertSame($expectedParams, $command->params);
     }
 
-    public function testInsert()
+    public function testInsert(): void
     {
         $db = $this->getConnection();
         $db->createCommand('DELETE FROM {{customer}}')->execute();
@@ -461,7 +467,7 @@ SQL;
     /**
      * verify that {{}} are not going to be replaced in parameters.
      */
-    public function testNoTablenameReplacement()
+    public function testNoTablenameReplacement(): void
     {
         $db = $this->getConnection();
 
@@ -498,7 +504,7 @@ SQL;
     /**
      * Test INSERT INTO ... SELECT SQL statement.
      */
-    public function testInsertSelect()
+    public function testInsertSelect(): void
     {
         $db = $this->getConnection();
         $db->createCommand('DELETE FROM {{customer}}')->execute();
@@ -513,7 +519,7 @@ SQL;
             ]
         )->execute();
 
-        $query = new \yii\db\Query();
+        $query = new Query();
         $query->select(
             [
                 '{{customer}}.[[email]] as name',
@@ -553,7 +559,7 @@ SQL;
     /**
      * Test INSERT INTO ... SELECT SQL statement with alias syntax.
      */
-    public function testInsertSelectAlias()
+    public function testInsertSelectAlias(): void
     {
         $db = $this->getConnection();
         $db->createCommand('DELETE FROM {{customer}}')->execute();
@@ -568,7 +574,7 @@ SQL;
             ]
         )->execute();
 
-        $query = new \yii\db\Query();
+        $query = new Query();
         $query->select(
             [
                 'email' => '{{customer}}.[[email]]',
@@ -625,15 +631,15 @@ SQL;
      *
      * @param mixed $invalidSelectColumns
      */
-    public function testInsertSelectFailed($invalidSelectColumns)
+    public function testInsertSelectFailed($invalidSelectColumns): void
     {
-        $query = new \yii\db\Query();
+        $query = new Query();
         $query->select($invalidSelectColumns)->from('{{customer}}');
 
         $db = $this->getConnection();
         $command = $db->createCommand();
 
-        $this->expectException(\yii\base\InvalidArgumentException::class);
+        $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Expected select query object with enumerated (named) parameters');
 
         $this->expectException('yii\base\InvalidParamException');
@@ -641,7 +647,7 @@ SQL;
         $command->insert('{{customer}}', $query)->execute();
     }
 
-    public function testInsertExpression()
+    public function testInsertExpression(): void
     {
         $db = $this->getConnection();
         $db->createCommand('DELETE FROM {{order_with_null_fk}}')->execute();
@@ -679,7 +685,7 @@ SQL;
         ], $record);
     }
 
-    public function testsInsertQueryAsColumnValue()
+    public function testsInsertQueryAsColumnValue(): void
     {
         $time = time();
 
@@ -698,7 +704,7 @@ SQL;
             $orderId = $db->getLastInsertID();
         }
 
-        $columnValueQuery = new \yii\db\Query();
+        $columnValueQuery = new Query();
         $columnValueQuery->select('created_at')->from('{{order}}')->where(['id' => $orderId]);
 
         $command = $db->createCommand();
@@ -717,7 +723,7 @@ SQL;
         $db->createCommand('DELETE FROM {{order}} WHERE [[id]] = ' . $orderId)->execute();
     }
 
-    public function testCreateTable()
+    public function testCreateTable(): void
     {
         $db = $this->getConnection();
 
@@ -733,7 +739,7 @@ SQL;
         ], $records);
     }
 
-    public function testAlterTable()
+    public function testAlterTable(): void
     {
         if ($this->driverName === 'sqlite') {
             $this->markTestSkipped('Sqlite does not support alterTable');
@@ -758,7 +764,7 @@ SQL;
         ], $records);
     }
 
-    public function testDropTable()
+    public function testDropTable(): void
     {
         $db = $this->getConnection();
 
@@ -768,7 +774,7 @@ SQL;
         $this->assertNull($db->getSchema()->getTableSchema($tableName));
     }
 
-    public function testTruncateTable()
+    public function testTruncateTable(): void
     {
         $db = $this->getConnection();
 
@@ -779,7 +785,7 @@ SQL;
         $this->assertCount(0, $rows);
     }
 
-    public function testRenameTable()
+    public function testRenameTable(): void
     {
         $db = $this->getConnection();
 
@@ -1026,7 +1032,7 @@ SQL;
      * @param array $firstData
      * @param array $secondData
      */
-    public function testUpsert(array $firstData, array $secondData)
+    public function testUpsert(array $firstData, array $secondData): void
     {
         $db = $this->getConnection();
         $this->assertEquals(0, $db->createCommand('SELECT COUNT(*) FROM {{T_upsert}}')->queryScalar());
@@ -1075,7 +1081,7 @@ SQL;
     }
     */
 
-    public function testAddDropPrimaryKey()
+    public function testAddDropPrimaryKey(): void
     {
         $db = $this->getConnection(false);
         $tableName = 'test_pk';
@@ -1102,7 +1108,7 @@ SQL;
         $this->assertEquals(['int1', 'int2'], $schema->getTablePrimaryKey($tableName, true)->columnNames);
     }
 
-    public function testAddDropForeignKey()
+    public function testAddDropForeignKey(): void
     {
         $db = $this->getConnection(false);
         $tableName = 'test_fk';
@@ -1135,7 +1141,7 @@ SQL;
         $this->assertEquals(['int3', 'int4'], $schema->getTableForeignKeys($tableName, true)[0]->foreignColumnNames);
     }
 
-    public function testCreateDropIndex()
+    public function testCreateDropIndex(): void
     {
         $db = $this->getConnection(false);
         $tableName = 'test_idx';
@@ -1179,7 +1185,7 @@ SQL;
         $this->assertTrue($schema->getTableIndexes($tableName, true)[0]->isUnique);
     }
 
-    public function testAddDropUnique()
+    public function testAddDropUnique(): void
     {
         $db = $this->getConnection(false);
         $tableName = 'test_uq';
@@ -1206,7 +1212,7 @@ SQL;
         $this->assertEquals(['int1', 'int2'], $schema->getTableUniques($tableName, true)[0]->columnNames);
     }
 
-    public function testAddDropCheck()
+    public function testAddDropCheck(): void
     {
         $db = $this->getConnection(false);
 
@@ -1237,12 +1243,12 @@ SQL;
         $this->assertEmpty($schema->getTableChecks($tableName, true));
     }
 
-    public function testAddDropDefaultValue()
+    public function testAddDropDefaultValue(): void
     {
         $this->markTestSkipped($this->driverName . ' does not support adding/dropping default value constraints.');
     }
 
-    public function testIntegrityViolation()
+    public function testIntegrityViolation(): void
     {
         $this->expectException('\yii\db\IntegrityException');
 
@@ -1254,7 +1260,7 @@ SQL;
         $command->execute();
     }
 
-    public function testLastInsertId()
+    public function testLastInsertId(): void
     {
         $db = $this->getConnection();
 
@@ -1264,7 +1270,7 @@ SQL;
         $this->assertEquals(3, $db->getSchema()->getLastInsertID());
     }
 
-    public function testQueryCache()
+    public function testQueryCache(): void
     {
         $db = $this->getConnection();
         $db->enableQueryCache = true;
@@ -1309,10 +1315,10 @@ SQL;
         }, 10);
     }
 
-    public function testColumnCase()
+    public function testColumnCase(): void
     {
         $db = $this->getConnection(false);
-        $this->assertEquals(\PDO::CASE_NATURAL, $db->slavePdo->getAttribute(\PDO::ATTR_CASE));
+        $this->assertEquals(PDO::CASE_NATURAL, $db->slavePdo->getAttribute(PDO::ATTR_CASE));
 
         $sql = 'SELECT [[customer_id]], [[total]] FROM {{order}}';
         $rows = $db->createCommand($sql)->queryAll();
@@ -1320,13 +1326,13 @@ SQL;
         $this->assertTrue(isset($rows[0]['customer_id']));
         $this->assertTrue(isset($rows[0]['total']));
 
-        $db->slavePdo->setAttribute(\PDO::ATTR_CASE, \PDO::CASE_LOWER);
+        $db->slavePdo->setAttribute(PDO::ATTR_CASE, PDO::CASE_LOWER);
         $rows = $db->createCommand($sql)->queryAll();
         $this->assertTrue(isset($rows[0]));
         $this->assertTrue(isset($rows[0]['customer_id']));
         $this->assertTrue(isset($rows[0]['total']));
 
-        $db->slavePdo->setAttribute(\PDO::ATTR_CASE, \PDO::CASE_UPPER);
+        $db->slavePdo->setAttribute(PDO::ATTR_CASE, PDO::CASE_UPPER);
         $rows = $db->createCommand($sql)->queryAll();
         $this->assertTrue(isset($rows[0]));
         $this->assertTrue(isset($rows[0]['CUSTOMER_ID']));
@@ -1397,14 +1403,14 @@ SQL;
      * @param array $params
      * @param string $expectedRawSql
      */
-    public function testGetRawSql($sql, array $params, $expectedRawSql)
+    public function testGetRawSql($sql, array $params, $expectedRawSql): void
     {
         $db = $this->getConnection(false);
         $command = $db->createCommand($sql, $params);
         $this->assertEquals($expectedRawSql, $command->getRawSql());
     }
 
-    public function testAutoRefreshTableSchema()
+    public function testAutoRefreshTableSchema(): void
     {
         if ($this->driverName === 'sqlsrv') {
             // related to https://github.com/yiisoft/yii2/pull/17364
@@ -1451,7 +1457,7 @@ SQL;
         $this->assertNull($db->getSchema()->getTableSchema($tableName));
     }
 
-    public function testTransaction()
+    public function testTransaction(): void
     {
         $connection = $this->getConnection(false);
         $this->assertNull($connection->transaction);
@@ -1462,7 +1468,7 @@ SQL;
         $this->assertEquals(1, $connection->createCommand("SELECT COUNT(*) FROM {{profile}} WHERE [[description]] = 'command transaction'")->queryScalar());
     }
 
-    public function testRetryHandler()
+    public function testRetryHandler(): void
     {
         $connection = $this->getConnection(false);
         $this->assertNull($connection->transaction);
@@ -1491,10 +1497,10 @@ SQL;
         $this->assertTrue($hitCatch);
     }
 
-    public function testCreateView()
+    public function testCreateView(): void
     {
         $db = $this->getConnection();
-        $subquery = (new \yii\db\Query())
+        $subquery = (new Query())
             ->select('bar')
             ->from('testCreateViewTable')
             ->where(['>', 'bar', '5']);
@@ -1516,7 +1522,7 @@ SQL;
         $this->assertEquals([['bar' => 6]], $records);
     }
 
-    public function testDropView()
+    public function testDropView(): void
     {
         $db = $this->getConnection();
         $viewName = 'animal_view'; // since it already exists in the fixtures
@@ -1527,26 +1533,26 @@ SQL;
     }
 
     // TODO: Remove in Yii 2.1
-    public function testBindValuesSupportsDeprecatedPDOCastingFormat()
+    public function testBindValuesSupportsDeprecatedPDOCastingFormat(): void
     {
         $db = $this->getConnection();
-        $db->createCommand()->setSql('SELECT :p1')->bindValues([':p1' => [2, \PDO::PARAM_STR]]);
+        $db->createCommand()->setSql('SELECT :p1')->bindValues([':p1' => [2, PDO::PARAM_STR]]);
         $this->assertTrue(true);
     }
 
-    public function testBindValuesSupportsEnums()
+    public function testBindValuesSupportsEnums(): void
     {
         if (version_compare(PHP_VERSION, '8.1.0') >= 0) {
             $db = $this->getConnection();
             $command = $db->createCommand();
 
-            $command->setSql('SELECT :p1')->bindValues([':p1' => enums\Status::Active]);
+            $command->setSql('SELECT :p1')->bindValues([':p1' => Status::Active]);
             $this->assertSame('Active', $command->params[':p1']);
 
-            $command->setSql('SELECT :p1')->bindValues([':p1' => enums\StatusTypeString::Active]);
+            $command->setSql('SELECT :p1')->bindValues([':p1' => StatusTypeString::Active]);
             $this->assertSame('active', $command->params[':p1']);
 
-            $command->setSql('SELECT :p1')->bindValues([':p1' => enums\StatusTypeInt::Active]);
+            $command->setSql('SELECT :p1')->bindValues([':p1' => StatusTypeInt::Active]);
             $this->assertSame(1, $command->params[':p1']);
         } else {
             $this->markTestSkipped('Enums are not supported in PHP < 8.1');
diff --git a/tests/framework/db/ConnectionTest.php b/tests/framework/db/ConnectionTest.php
index 23ef80bbb1..7e937310fb 100644
--- a/tests/framework/db/ConnectionTest.php
+++ b/tests/framework/db/ConnectionTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\db;
 
+use Exception;
 use Yii;
 use yii\base\InvalidConfigException;
 use yii\caching\ArrayCache;
@@ -18,7 +19,7 @@ use yii\db\Transaction;
 
 abstract class ConnectionTest extends DatabaseTestCase
 {
-    public function testConstruct()
+    public function testConstruct(): void
     {
         $connection = $this->getConnection(false);
         $params = $this->database;
@@ -28,7 +29,7 @@ abstract class ConnectionTest extends DatabaseTestCase
         $this->assertEquals($params['password'], $connection->password);
     }
 
-    public function testOpenClose()
+    public function testOpenClose(): void
     {
         $connection = $this->getConnection(false, false);
 
@@ -49,7 +50,7 @@ abstract class ConnectionTest extends DatabaseTestCase
         $connection->open();
     }
 
-    public function testQueryBuilderConfigurationAfterOpenClose()
+    public function testQueryBuilderConfigurationAfterOpenClose(): void
     {
         $connection = $this->getConnection(false, false);
         $connection->setQueryBuilder([
@@ -93,7 +94,7 @@ abstract class ConnectionTest extends DatabaseTestCase
         );
     }
 
-    public function testSerialize()
+    public function testSerialize(): void
     {
         $connection = $this->getConnection(false, false);
         $connection->open();
@@ -108,13 +109,13 @@ abstract class ConnectionTest extends DatabaseTestCase
         $this->assertEquals(123, $unserialized->createCommand('SELECT 123')->queryScalar());
     }
 
-    public function testGetDriverName()
+    public function testGetDriverName(): void
     {
         $connection = $this->getConnection(false, false);
         $this->assertEquals($this->driverName, $connection->driverName);
     }
 
-    public function testQuoteValue()
+    public function testQuoteValue(): void
     {
         $connection = $this->getConnection(false);
         $this->assertEquals(123, $connection->quoteValue(123));
@@ -122,7 +123,7 @@ abstract class ConnectionTest extends DatabaseTestCase
         $this->assertEquals("'It\\'s interesting'", $connection->quoteValue("It's interesting"));
     }
 
-    public function testQuoteTableName()
+    public function testQuoteTableName(): void
     {
         $connection = $this->getConnection(false, false);
         $this->assertEquals('`table`', $connection->quoteTableName('table'));
@@ -135,7 +136,7 @@ abstract class ConnectionTest extends DatabaseTestCase
         $this->assertEquals('`table(0)`', $connection->quoteTableName('table(0)'));
     }
 
-    public function testQuoteColumnName()
+    public function testQuoteColumnName(): void
     {
         $connection = $this->getConnection(false, false);
         $this->assertEquals('`column`', $connection->quoteColumnName('column'));
@@ -148,7 +149,7 @@ abstract class ConnectionTest extends DatabaseTestCase
         $this->assertEquals('`column`', $connection->quoteSql('{{column}}'));
     }
 
-    public function testQuoteFullColumnName()
+    public function testQuoteFullColumnName(): void
     {
         $connection = $this->getConnection(false, false);
         $this->assertEquals('`table`.`column`', $connection->quoteColumnName('table.column'));
@@ -170,7 +171,7 @@ abstract class ConnectionTest extends DatabaseTestCase
         $this->assertEquals('`table`.`column`', $connection->quoteSql('{{%table}}.`column`'));
     }
 
-    public function testTransaction()
+    public function testTransaction(): void
     {
         $connection = $this->getConnection(false);
         $this->assertNull($connection->transaction);
@@ -205,7 +206,7 @@ abstract class ConnectionTest extends DatabaseTestCase
         );
     }
 
-    public function testTransactionIsolation()
+    public function testTransactionIsolation(): void
     {
         $connection = $this->getConnection(true);
 
@@ -224,15 +225,15 @@ abstract class ConnectionTest extends DatabaseTestCase
         $this->assertTrue(true); // should not be any exception so far
     }
 
-    public function testTransactionShortcutException()
+    public function testTransactionShortcutException(): void
     {
         $connection = $this->getConnection(true);
 
-        $this->expectException(\Exception::class);
+        $this->expectException(Exception::class);
 
         $connection->transaction(function () use ($connection) {
             $connection->createCommand()->insert('profile', ['description' => 'test transaction shortcut'])->execute();
-            throw new \Exception('Exception in transaction shortcut');
+            throw new Exception('Exception in transaction shortcut');
         });
 
         $profilesCount = $connection
@@ -241,7 +242,7 @@ abstract class ConnectionTest extends DatabaseTestCase
         $this->assertEquals(0, $profilesCount, 'profile should not be inserted in transaction shortcut');
     }
 
-    public function testTransactionShortcutCorrect()
+    public function testTransactionShortcutCorrect(): void
     {
         $connection = $this->getConnection(true);
 
@@ -259,7 +260,7 @@ abstract class ConnectionTest extends DatabaseTestCase
         $this->assertEquals(1, $profilesCount, 'profile should be inserted in transaction shortcut');
     }
 
-    public function testTransactionShortcutCustom()
+    public function testTransactionShortcutCustom(): void
     {
         $connection = $this->getConnection(true);
 
@@ -278,7 +279,7 @@ abstract class ConnectionTest extends DatabaseTestCase
      * Tests nested transactions with partial rollback.
      * @see https://github.com/yiisoft/yii2/issues/9851
      */
-    public function testNestedTransaction()
+    public function testNestedTransaction(): void
     {
         /** @var Connection $connection */
         $connection = $this->getConnection(true);
@@ -292,7 +293,7 @@ abstract class ConnectionTest extends DatabaseTestCase
         });
     }
 
-    public function testNestedTransactionNotSupported()
+    public function testNestedTransactionNotSupported(): void
     {
         $connection = $this->getConnection();
         $connection->enableSavepoint = false;
@@ -303,7 +304,7 @@ abstract class ConnectionTest extends DatabaseTestCase
         });
     }
 
-    public function testEnableQueryLog()
+    public function testEnableQueryLog(): void
     {
         $connection = $this->getConnection();
         foreach (['qlog1', 'qlog2', 'qlog3', 'qlog4'] as $table) {
@@ -316,54 +317,54 @@ abstract class ConnectionTest extends DatabaseTestCase
         $connection->enableLogging = true;
         $connection->enableProfiling = true;
 
-        \Yii::getLogger()->messages = [];
+        Yii::getLogger()->messages = [];
         $connection->createCommand()->createTable('qlog1', ['id' => 'pk'])->execute();
-        $this->assertCount(3, \Yii::getLogger()->messages);
+        $this->assertCount(3, Yii::getLogger()->messages);
         $this->assertNotNull($connection->getTableSchema('qlog1', true));
 
-        \Yii::getLogger()->messages = [];
+        Yii::getLogger()->messages = [];
         $connection->createCommand('SELECT * FROM {{qlog1}}')->queryAll();
-        $this->assertCount(3, \Yii::getLogger()->messages);
+        $this->assertCount(3, Yii::getLogger()->messages);
 
         // profiling only
         $connection->enableLogging = false;
         $connection->enableProfiling = true;
 
-        \Yii::getLogger()->messages = [];
+        Yii::getLogger()->messages = [];
         $connection->createCommand()->createTable('qlog2', ['id' => 'pk'])->execute();
-        $this->assertCount(2, \Yii::getLogger()->messages);
+        $this->assertCount(2, Yii::getLogger()->messages);
         $this->assertNotNull($connection->getTableSchema('qlog2', true));
 
-        \Yii::getLogger()->messages = [];
+        Yii::getLogger()->messages = [];
         $connection->createCommand('SELECT * FROM {{qlog2}}')->queryAll();
-        $this->assertCount(2, \Yii::getLogger()->messages);
+        $this->assertCount(2, Yii::getLogger()->messages);
 
         // logging only
         $connection->enableLogging = true;
         $connection->enableProfiling = false;
 
-        \Yii::getLogger()->messages = [];
+        Yii::getLogger()->messages = [];
         $connection->createCommand()->createTable('qlog3', ['id' => 'pk'])->execute();
-        $this->assertCount(1, \Yii::getLogger()->messages);
+        $this->assertCount(1, Yii::getLogger()->messages);
         $this->assertNotNull($connection->getTableSchema('qlog3', true));
 
-        \Yii::getLogger()->messages = [];
+        Yii::getLogger()->messages = [];
         $connection->createCommand('SELECT * FROM {{qlog3}}')->queryAll();
-        $this->assertCount(1, \Yii::getLogger()->messages);
+        $this->assertCount(1, Yii::getLogger()->messages);
 
         // disabled
         $connection->enableLogging = false;
         $connection->enableProfiling = false;
 
-        \Yii::getLogger()->messages = [];
+        Yii::getLogger()->messages = [];
         $connection->createCommand()->createTable('qlog4', ['id' => 'pk'])->execute();
         $this->assertNotNull($connection->getTableSchema('qlog4', true));
-        $this->assertCount(0, \Yii::getLogger()->messages);
+        $this->assertCount(0, Yii::getLogger()->messages);
         $connection->createCommand('SELECT * FROM {{qlog4}}')->queryAll();
-        $this->assertCount(0, \Yii::getLogger()->messages);
+        $this->assertCount(0, Yii::getLogger()->messages);
     }
 
-    public function testExceptionContainsRawQuery()
+    public function testExceptionContainsRawQuery(): void
     {
         $connection = $this->getConnection();
         if ($connection->getTableSchema('qlog1', true) === null) {
@@ -396,7 +397,7 @@ abstract class ConnectionTest extends DatabaseTestCase
     /**
      * @param Connection $connection
      */
-    private function runExceptionTest($connection)
+    private function runExceptionTest($connection): void
     {
         $thrown = false;
         try {
@@ -430,7 +431,7 @@ abstract class ConnectionTest extends DatabaseTestCase
      * Make sure each connection element has its own PDO instance i.e. own connection to the DB.
      * Also transaction elements should not be shared between two connections.
      */
-    public function testClone()
+    public function testClone(): void
     {
         $connection = $this->getConnection(true, false);
         $this->assertNull($connection->transaction);
@@ -482,7 +483,7 @@ abstract class ConnectionTest extends DatabaseTestCase
      *
      * @see https://github.com/yiisoft/yii2/issues/14165
      */
-    public function testGetPdoAfterClose()
+    public function testGetPdoAfterClose(): void
     {
         $connection = $this->getConnection();
         $connection->slaves[] = [
@@ -503,7 +504,7 @@ abstract class ConnectionTest extends DatabaseTestCase
         $this->assertNotSame($masterPdo, $slavePdo);
     }
 
-    public function testServerStatusCacheWorks()
+    public function testServerStatusCacheWorks(): void
     {
         $cache = new ArrayCache();
         Yii::$app->set('cache', $cache);
@@ -533,7 +534,7 @@ abstract class ConnectionTest extends DatabaseTestCase
         $connection->close();
     }
 
-    public function testServerStatusCacheCanBeDisabled()
+    public function testServerStatusCacheCanBeDisabled(): void
     {
         $cache = new ArrayCache();
         Yii::$app->set('cache', $cache);
diff --git a/tests/framework/db/DatabaseTestCase.php b/tests/framework/db/DatabaseTestCase.php
index 1d0d7d9347..23ffac69ed 100644
--- a/tests/framework/db/DatabaseTestCase.php
+++ b/tests/framework/db/DatabaseTestCase.php
@@ -8,6 +8,8 @@
 
 namespace yiiunit\framework\db;
 
+use Exception;
+use Yii;
 use yii\caching\DummyCache;
 use yii\db\Connection;
 use yiiunit\TestCase;
@@ -27,7 +29,7 @@ abstract class DatabaseTestCase extends TestCase
     protected function setUp(): void
     {
         if ($this->driverName === null) {
-            throw new \Exception('driverName is not set for a DatabaseTestCase.');
+            throw new Exception('driverName is not set for a DatabaseTestCase.');
         }
 
         parent::setUp();
@@ -55,7 +57,7 @@ abstract class DatabaseTestCase extends TestCase
     /**
      * @param  bool $reset whether to clean up the test database
      * @param  bool $open  whether to open and populate test database
-     * @return \yii\db\Connection
+     * @return Connection
      */
     public function getConnection($reset = true, $open = true)
     {
@@ -71,7 +73,7 @@ abstract class DatabaseTestCase extends TestCase
         }
         try {
             $this->_db = $this->prepareDatabase($config, $fixture, $open);
-        } catch (\Exception $e) {
+        } catch (Exception $e) {
             $this->markTestSkipped('Something wrong when preparing database: ' . $e->getMessage());
         }
 
@@ -83,8 +85,8 @@ abstract class DatabaseTestCase extends TestCase
         if (!isset($config['class'])) {
             $config['class'] = 'yii\db\Connection';
         }
-        /** @var \yii\db\Connection $db */
-        $db = \Yii::createObject($config);
+        /** @var Connection $db */
+        $db = Yii::createObject($config);
         if (!$open) {
             return $db;
         }
@@ -132,7 +134,7 @@ abstract class DatabaseTestCase extends TestCase
     }
 
     /**
-     * @return \yii\db\Connection
+     * @return Connection
      */
     protected function getConnectionWithInvalidSlave()
     {
diff --git a/tests/framework/db/GetTablesAliasTestTrait.php b/tests/framework/db/GetTablesAliasTestTrait.php
index 5b8f04fdad..831c97147e 100644
--- a/tests/framework/db/GetTablesAliasTestTrait.php
+++ b/tests/framework/db/GetTablesAliasTestTrait.php
@@ -8,6 +8,8 @@
 
 namespace yiiunit\framework\db;
 
+use stdClass;
+use yii\db\Expression;
 use yii\db\ActiveQuery;
 use yii\db\Query;
 
@@ -18,7 +20,7 @@ trait GetTablesAliasTestTrait
      */
     abstract protected function createQuery();
 
-    public function testGetTableNames_isFromArrayWithAlias()
+    public function testGetTableNames_isFromArrayWithAlias(): void
     {
         $query = $this->createQuery();
         $query->from = [
@@ -38,7 +40,7 @@ trait GetTablesAliasTestTrait
         ], $tables);
     }
 
-    public function testGetTableNames_isFromArrayWithoutAlias()
+    public function testGetTableNames_isFromArrayWithoutAlias(): void
     {
         $query = $this->createQuery();
         $query->from = [
@@ -54,7 +56,7 @@ trait GetTablesAliasTestTrait
         ], $tables);
     }
 
-    public function testGetTableNames_isFromString()
+    public function testGetTableNames_isFromString(): void
     {
         $query = $this->createQuery();
         $query->from = 'profile AS \'prf\', user "usr", `order`, "customer", "a b" as "c d"';
@@ -70,17 +72,17 @@ trait GetTablesAliasTestTrait
         ], $tables);
     }
 
-    public function testGetTableNames_isFromObject_generateException()
+    public function testGetTableNames_isFromObject_generateException(): void
     {
         $query = $this->createQuery();
-        $query->from = new \stdClass();
+        $query->from = new stdClass();
 
         $this->expectException('\yii\base\InvalidConfigException');
 
         $query->getTablesUsedInFrom();
     }
 
-    public function testGetTablesAlias_isFromString()
+    public function testGetTablesAlias_isFromString(): void
     {
         $query = $this->createQuery();
         $query->from = 'profile AS \'prf\', user "usr", service srv, order, [a b] [c d], {{something}} AS myalias';
@@ -100,7 +102,7 @@ trait GetTablesAliasTestTrait
     /**
      * @see https://github.com/yiisoft/yii2/issues/14150
      */
-    public function testGetTableNames_isFromPrefixedTableName()
+    public function testGetTableNames_isFromPrefixedTableName(): void
     {
         $query = $this->createQuery();
         $query->from = '{{%order_item}}';
@@ -115,7 +117,7 @@ trait GetTablesAliasTestTrait
     /**
      * @see https://github.com/yiisoft/yii2/issues/14211
      */
-    public function testGetTableNames_isFromTableNameWithDatabase()
+    public function testGetTableNames_isFromTableNameWithDatabase(): void
     {
         $query = $this->createQuery();
         $query->from = 'tickets.workflows';
@@ -127,10 +129,10 @@ trait GetTablesAliasTestTrait
         ], $tables);
     }
 
-    public function testGetTableNames_isFromAliasedExpression()
+    public function testGetTableNames_isFromAliasedExpression(): void
     {
         $query = $this->createQuery();
-        $expression = new \yii\db\Expression('(SELECT id FROM user)');
+        $expression = new Expression('(SELECT id FROM user)');
         $query->from = $expression;
 
         $this->expectException('yii\base\InvalidParamException');
@@ -140,10 +142,10 @@ trait GetTablesAliasTestTrait
         $this->assertEquals(['{{x}}' => $expression], $tables);
     }
 
-    public function testGetTableNames_isFromAliasedArrayWithExpression()
+    public function testGetTableNames_isFromAliasedArrayWithExpression(): void
     {
         $query = $this->createQuery();
-        $query->from = ['x' => new \yii\db\Expression('(SELECT id FROM user)')];
+        $query->from = ['x' => new Expression('(SELECT id FROM user)')];
 
         $tables = $query->getTablesUsedInFrom();
 
@@ -152,7 +154,7 @@ trait GetTablesAliasTestTrait
         ], $tables);
     }
 
-    public function testGetTableNames_isFromAliasedSubquery()
+    public function testGetTableNames_isFromAliasedSubquery(): void
     {
         $query = $this->createQuery();
         $subQuery = $this->createQuery();
diff --git a/tests/framework/db/QueryBuilderTest.php b/tests/framework/db/QueryBuilderTest.php
index e0fb82cfa0..2699db38a3 100644
--- a/tests/framework/db/QueryBuilderTest.php
+++ b/tests/framework/db/QueryBuilderTest.php
@@ -8,6 +8,10 @@
 
 namespace yiiunit\framework\db;
 
+use Yii;
+use Exception;
+use Closure;
+use yii\base\NotSupportedException;
 use yii\db\ColumnSchemaBuilder;
 use yii\db\conditions\BetweenColumnsCondition;
 use yii\db\conditions\LikeCondition;
@@ -48,13 +52,13 @@ abstract class QueryBuilderTest extends DatabaseTestCase
      * @param bool $reset
      * @param bool $open
      * @return QueryBuilder
-     * @throws \Exception
+     * @throws Exception
      */
     protected function getQueryBuilder($reset = true, $open = false)
     {
         $connection = $this->getConnection($reset, $open);
 
-        \Yii::$container->set('db', $connection);
+        Yii::$container->set('db', $connection);
 
         switch ($this->driverName) {
             case 'mysql':
@@ -70,7 +74,7 @@ abstract class QueryBuilderTest extends DatabaseTestCase
             case 'oci':
                 return new OracleQueryBuilder($connection);
         }
-        throw new \Exception('Test is not implemented for ' . $this->driverName);
+        throw new Exception('Test is not implemented for ' . $this->driverName);
     }
 
     /**
@@ -1060,7 +1064,7 @@ abstract class QueryBuilderTest extends DatabaseTestCase
         return array_values($items);
     }
 
-    public function testGetColumnType()
+    public function testGetColumnType(): void
     {
         $qb = $this->getQueryBuilder();
 
@@ -1081,7 +1085,7 @@ abstract class QueryBuilderTest extends DatabaseTestCase
         }
     }
 
-    public function testCreateTableColumnTypes()
+    public function testCreateTableColumnTypes(): void
     {
         $qb = $this->getQueryBuilder();
         if ($qb->db->getTableSchema('column_type_table', true) !== null) {
@@ -1321,9 +1325,9 @@ abstract class QueryBuilderTest extends DatabaseTestCase
      * @dataProvider buildFromDataProvider
      * @param $table
      * @param $expected
-     * @throws \Exception
+     * @throws Exception
      */
-    public function testBuildFrom($table, $expected)
+    public function testBuildFrom($table, $expected): void
     {
         $params = [];
         $sql = $this->getQueryBuilder()->buildFrom([$table], $params);
@@ -1345,9 +1349,9 @@ abstract class QueryBuilderTest extends DatabaseTestCase
      * @param array $condition
      * @param string $expected
      * @param array $expectedParams
-     * @throws \Exception
+     * @throws Exception
      */
-    public function testBuildCondition($condition, $expected, $expectedParams)
+    public function testBuildCondition($condition, $expected, $expectedParams): void
     {
         $query = (new Query())->where($condition);
         list($sql, $params) = $this->getQueryBuilder()->build($query);
@@ -1361,7 +1365,7 @@ abstract class QueryBuilderTest extends DatabaseTestCase
      * @param string $expected
      * @param array $expectedParams
      */
-    public function testBuildFilterCondition($condition, $expected, $expectedParams)
+    public function testBuildFilterCondition($condition, $expected, $expectedParams): void
     {
         $query = (new Query())->filterWhere($condition);
         list($sql, $params) = $this->getQueryBuilder()->build($query);
@@ -1399,7 +1403,7 @@ abstract class QueryBuilderTest extends DatabaseTestCase
      * @dataProvider primaryKeysProvider
      * @param string $sql
      */
-    public function testAddDropPrimaryKey($sql, \Closure $builder)
+    public function testAddDropPrimaryKey($sql, Closure $builder): void
     {
         $this->assertSame($this->getConnection(false)->quoteSql($sql), $builder($this->getQueryBuilder(false)));
     }
@@ -1435,7 +1439,7 @@ abstract class QueryBuilderTest extends DatabaseTestCase
      * @dataProvider foreignKeysProvider
      * @param string $sql
      */
-    public function testAddDropForeignKey($sql, \Closure $builder)
+    public function testAddDropForeignKey($sql, Closure $builder): void
     {
         $this->assertSame($this->getConnection(false)->quoteSql($sql), $builder($this->getQueryBuilder(false)));
     }
@@ -1483,7 +1487,7 @@ abstract class QueryBuilderTest extends DatabaseTestCase
      * @dataProvider indexesProvider
      * @param string $sql
      */
-    public function testCreateDropIndex($sql, \Closure $builder)
+    public function testCreateDropIndex($sql, Closure $builder): void
     {
         $this->assertSame($this->getConnection(false)->quoteSql($sql), $builder($this->getQueryBuilder(false)));
     }
@@ -1520,7 +1524,7 @@ abstract class QueryBuilderTest extends DatabaseTestCase
      * @dataProvider uniquesProvider
      * @param string $sql
      */
-    public function testAddDropUnique($sql, \Closure $builder)
+    public function testAddDropUnique($sql, Closure $builder): void
     {
         $this->assertSame($this->getConnection(false)->quoteSql($sql), $builder($this->getQueryBuilder(false)));
     }
@@ -1549,7 +1553,7 @@ abstract class QueryBuilderTest extends DatabaseTestCase
      * @dataProvider checksProvider
      * @param string $sql
      */
-    public function testAddDropCheck($sql, \Closure $builder)
+    public function testAddDropCheck($sql, Closure $builder): void
     {
         $this->assertSame($this->getConnection(false)->quoteSql($sql), $builder($this->getQueryBuilder(false)));
     }
@@ -1578,7 +1582,7 @@ abstract class QueryBuilderTest extends DatabaseTestCase
      * @dataProvider defaultValuesProvider
      * @param string $sql
      */
-    public function testAddDropDefaultValue($sql, \Closure $builder)
+    public function testAddDropDefaultValue($sql, Closure $builder): void
     {
         $this->assertSame($this->getConnection(false)->quoteSql($sql), $builder($this->getQueryBuilder(false)));
     }
@@ -1596,7 +1600,7 @@ abstract class QueryBuilderTest extends DatabaseTestCase
      * @param string $cond
      * @param string $expectedQuerySql
      */
-    public function testBuildWhereExists($cond, $expectedQuerySql)
+    public function testBuildWhereExists($cond, $expectedQuerySql): void
     {
         $expectedQueryParams = [];
 
@@ -1614,7 +1618,7 @@ abstract class QueryBuilderTest extends DatabaseTestCase
         $this->assertEquals($expectedQueryParams, $actualQueryParams);
     }
 
-    public function testBuildWhereExistsWithParameters()
+    public function testBuildWhereExistsWithParameters(): void
     {
         $expectedQuerySql = $this->replaceQuotes(
             'SELECT [[id]] FROM [[TotalExample]] [[t]] WHERE (EXISTS (SELECT [[1]] FROM [[Website]] [[w]] WHERE (w.id = t.website_id) AND (w.merchant_id = :merchant_id))) AND (t.some_column = :some_value)'
@@ -1638,7 +1642,7 @@ abstract class QueryBuilderTest extends DatabaseTestCase
         $this->assertEquals($expectedQueryParams, $queryParams);
     }
 
-    public function testBuildWhereExistsWithArrayParameters()
+    public function testBuildWhereExistsWithArrayParameters(): void
     {
         $expectedQuerySql = $this->replaceQuotes(
             'SELECT [[id]] FROM [[TotalExample]] [[t]] WHERE (EXISTS (SELECT [[1]] FROM [[Website]] [[w]] WHERE (w.id = t.website_id) AND (([[w]].[[merchant_id]]=:qp0) AND ([[w]].[[user_id]]=:qp1)))) AND ([[t]].[[some_column]]=:qp2)'
@@ -1666,7 +1670,7 @@ abstract class QueryBuilderTest extends DatabaseTestCase
      * This test contains three select queries connected with UNION and UNION ALL constructions.
      * It could be useful to use "phpunit --group=db --filter testBuildUnion" command for run it.
      */
-    public function testBuildUnion()
+    public function testBuildUnion(): void
     {
         $expectedQuerySql = $this->replaceQuotes(
             '(SELECT [[id]] FROM [[TotalExample]] [[t1]] WHERE (w > 0) AND (x < 2)) UNION ( SELECT [[id]] FROM [[TotalTotalExample]] [[t2]] WHERE w > 5 ) UNION ALL ( SELECT [[id]] FROM [[TotalTotalExample]] [[t3]] WHERE w = 3 )'
@@ -1690,7 +1694,7 @@ abstract class QueryBuilderTest extends DatabaseTestCase
         $this->assertEquals([], $queryParams);
     }
 
-    public function testBuildWithQuery()
+    public function testBuildWithQuery(): void
     {
         $expectedQuerySql = $this->replaceQuotes(
             'WITH a1 AS (SELECT [[id]] FROM [[t1]] WHERE expr = 1), a2 AS ((SELECT [[id]] FROM [[t2]] INNER JOIN [[a1]] ON t2.id = a1.id WHERE expr = 2) UNION ( SELECT [[id]] FROM [[t3]] WHERE expr = 3 )) SELECT * FROM [[a2]]'
@@ -1721,7 +1725,7 @@ abstract class QueryBuilderTest extends DatabaseTestCase
         $this->assertEquals([], $queryParams);
     }
 
-    public function testBuildWithQueryRecursive()
+    public function testBuildWithQueryRecursive(): void
     {
         $expectedQuerySql = $this->replaceQuotes(
             'WITH RECURSIVE a1 AS (SELECT [[id]] FROM [[t1]] WHERE expr = 1) SELECT * FROM [[a1]]'
@@ -1740,7 +1744,7 @@ abstract class QueryBuilderTest extends DatabaseTestCase
         $this->assertEquals([], $queryParams);
     }
 
-    public function testSelectSubquery()
+    public function testSelectSubquery(): void
     {
         $subquery = (new Query())
             ->select('COUNT(*)')
@@ -1756,7 +1760,7 @@ abstract class QueryBuilderTest extends DatabaseTestCase
         $this->assertEmpty($params);
     }
 
-    public function testComplexSelect()
+    public function testComplexSelect(): void
     {
         $query = (new Query())
             ->select([
@@ -1777,7 +1781,7 @@ abstract class QueryBuilderTest extends DatabaseTestCase
         $this->assertEmpty($params);
     }
 
-    public function testSelectExpression()
+    public function testSelectExpression(): void
     {
         $query = (new Query())
             ->select(new Expression('1 AS ab'))
@@ -1809,7 +1813,7 @@ abstract class QueryBuilderTest extends DatabaseTestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/10869
      */
-    public function testFromIndexHint()
+    public function testFromIndexHint(): void
     {
         $query = (new Query())->from([new Expression('{{%user}} USE INDEX (primary)')]);
         list($sql, $params) = $this->getQueryBuilder()->build($query);
@@ -1826,7 +1830,7 @@ abstract class QueryBuilderTest extends DatabaseTestCase
         $this->assertEmpty($params);
     }
 
-    public function testFromSubquery()
+    public function testFromSubquery(): void
     {
         // query subquery
         $subquery = (new Query())->from('user')->where('account_id = accounts.id');
@@ -1859,7 +1863,7 @@ abstract class QueryBuilderTest extends DatabaseTestCase
         $this->assertEmpty($params);
     }
 
-    public function testOrderBy()
+    public function testOrderBy(): void
     {
         // simple string
         $query = (new Query())
@@ -1903,7 +1907,7 @@ abstract class QueryBuilderTest extends DatabaseTestCase
         $this->assertEquals([':to' => 4], $params);
     }
 
-    public function testGroupBy()
+    public function testGroupBy(): void
     {
         // simple string
         $query = (new Query())
@@ -2044,7 +2048,7 @@ abstract class QueryBuilderTest extends DatabaseTestCase
      * @param string $expectedSQL
      * @param array $expectedParams
      */
-    public function testInsert($table, $columns, $params, $expectedSQL, $expectedParams)
+    public function testInsert($table, $columns, $params, $expectedSQL, $expectedParams): void
     {
         $actualParams = $params;
         $actualSQL = $this->getQueryBuilder()->insert($table, $columns, $actualParams);
@@ -2055,7 +2059,7 @@ abstract class QueryBuilderTest extends DatabaseTestCase
     /**
      * Dummy test to speed up QB's tests which rely on DB schema
      */
-    public function testInitFixtures()
+    public function testInitFixtures(): void
     {
         $this->assertInstanceOf('yii\db\QueryBuilder', $this->getQueryBuilder(true, true));
     }
@@ -2268,10 +2272,10 @@ abstract class QueryBuilderTest extends DatabaseTestCase
      * @param array|null $updateColumns
      * @param string|string[] $expectedSQL
      * @param array $expectedParams
-     * @throws \yii\base\NotSupportedException
-     * @throws \Exception
+     * @throws NotSupportedException
+     * @throws Exception
      */
-    public function testUpsert($table, $insertColumns, $updateColumns, $expectedSQL, $expectedParams)
+    public function testUpsert($table, $insertColumns, $updateColumns, $expectedSQL, $expectedParams): void
     {
         $actualParams = [];
         $actualSQL = $this->getQueryBuilder(true, $this->driverName === 'sqlite')->upsert($table, $insertColumns, $updateColumns, $actualParams);
@@ -2341,9 +2345,9 @@ abstract class QueryBuilderTest extends DatabaseTestCase
      * @param array $columns
      * @param array $value
      * @param string $expected
-     * @throws \Exception
+     * @throws Exception
      */
-    public function testBatchInsert($table, $columns, $value, $expected)
+    public function testBatchInsert($table, $columns, $value, $expected): void
     {
         $queryBuilder = $this->getQueryBuilder();
 
@@ -2380,7 +2384,7 @@ abstract class QueryBuilderTest extends DatabaseTestCase
      * @param string $expectedSQL
      * @param array $expectedParams
      */
-    public function testUpdate($table, $columns, $condition, $expectedSQL, $expectedParams)
+    public function testUpdate($table, $columns, $condition, $expectedSQL, $expectedParams): void
     {
         $actualParams = [];
         $actualSQL = $this->getQueryBuilder()->update($table, $columns, $condition, $actualParams);
@@ -2412,7 +2416,7 @@ abstract class QueryBuilderTest extends DatabaseTestCase
      * @param string $expectedSQL
      * @param array $expectedParams
      */
-    public function testDelete($table, $condition, $expectedSQL, $expectedParams)
+    public function testDelete($table, $condition, $expectedSQL, $expectedParams): void
     {
         $actualParams = [];
         $actualSQL = $this->getQueryBuilder()->delete($table, $condition, $actualParams);
@@ -2420,7 +2424,7 @@ abstract class QueryBuilderTest extends DatabaseTestCase
         $this->assertSame($expectedParams, $actualParams);
     }
 
-    public function testCommentColumn()
+    public function testCommentColumn(): void
     {
         $qb = $this->getQueryBuilder();
 
@@ -2437,7 +2441,7 @@ abstract class QueryBuilderTest extends DatabaseTestCase
         $this->assertEquals($this->replaceQuotes($expected), $sql);
     }
 
-    public function testCommentTable()
+    public function testCommentTable(): void
     {
         $qb = $this->getQueryBuilder();
 
@@ -2518,7 +2522,7 @@ abstract class QueryBuilderTest extends DatabaseTestCase
      * @param string $expected
      * @param array $expectedParams
      */
-    public function testBuildLikeCondition($condition, $expected, $expectedParams)
+    public function testBuildLikeCondition($condition, $expected, $expectedParams): void
     {
         $query = (new Query())->where($condition);
         list($sql, $params) = $this->getQueryBuilder()->build($query);
@@ -2529,7 +2533,7 @@ abstract class QueryBuilderTest extends DatabaseTestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/15653
      */
-    public function testIssue15653()
+    public function testIssue15653(): void
     {
         $query = (new Query())
             ->from('admin_user')
diff --git a/tests/framework/db/QueryTest.php b/tests/framework/db/QueryTest.php
index fb4a08645f..6b007abe40 100644
--- a/tests/framework/db/QueryTest.php
+++ b/tests/framework/db/QueryTest.php
@@ -18,7 +18,7 @@ abstract class QueryTest extends DatabaseTestCase
 {
     use GetTablesAliasTestTrait;
 
-    public function testSelect()
+    public function testSelect(): void
     {
         // default
         $query = new Query();
@@ -107,14 +107,14 @@ abstract class QueryTest extends DatabaseTestCase
         $this->assertEquals(['DISTINCT ON(tour_dates.date_from) tour_dates.date_from', 'tour_dates.id' => 'tour_dates.id'], $query->select);
     }
 
-    public function testFrom()
+    public function testFrom(): void
     {
         $query = new Query();
         $query->from('user');
         $this->assertEquals(['user'], $query->from);
     }
 
-    public function testFromTableIsArrayWithExpression()
+    public function testFromTableIsArrayWithExpression(): void
     {
         $query = new Query();
         $tables = new Expression('(SELECT id,name FROM user) u');
@@ -127,7 +127,7 @@ abstract class QueryTest extends DatabaseTestCase
         return new Query();
     }
 
-    public function testWhere()
+    public function testWhere(): void
     {
         $query = new Query();
         $query->where('id = :id', [':id' => 1]);
@@ -143,7 +143,7 @@ abstract class QueryTest extends DatabaseTestCase
         $this->assertEquals([':id' => 1, ':name' => 'something', ':age' => '30'], $query->params);
     }
 
-    public function testFilterWhereWithHashFormat()
+    public function testFilterWhereWithHashFormat(): void
     {
         $query = new Query();
         $query->filterWhere([
@@ -160,7 +160,7 @@ abstract class QueryTest extends DatabaseTestCase
         $this->assertEquals(['id' => 0], $query->where);
     }
 
-    public function testFilterWhereWithOperatorFormat()
+    public function testFilterWhereWithOperatorFormat(): void
     {
         $query = new Query();
         $condition = ['like', 'name', 'Alex'];
@@ -195,7 +195,7 @@ abstract class QueryTest extends DatabaseTestCase
         $this->assertEquals($condition, $query->where);
     }
 
-    public function testFilterHavingWithHashFormat()
+    public function testFilterHavingWithHashFormat(): void
     {
         $query = new Query();
         $query->filterHaving([
@@ -212,7 +212,7 @@ abstract class QueryTest extends DatabaseTestCase
         $this->assertEquals(['id' => 0], $query->having);
     }
 
-    public function testFilterHavingWithOperatorFormat()
+    public function testFilterHavingWithOperatorFormat(): void
     {
         $query = new Query();
         $condition = ['like', 'name', 'Alex'];
@@ -247,7 +247,7 @@ abstract class QueryTest extends DatabaseTestCase
         $this->assertEquals($condition, $query->having);
     }
 
-    public function testFilterRecursively()
+    public function testFilterRecursively(): void
     {
         $query = new Query();
         $query->filterWhere(['and', ['like', 'name', ''], ['like', 'title', ''], ['id' => 1], ['not', ['like', 'name', '']]]);
@@ -258,7 +258,7 @@ abstract class QueryTest extends DatabaseTestCase
     {
     }*/
 
-    public function testGroup()
+    public function testGroup(): void
     {
         $query = new Query();
         $query->groupBy('team');
@@ -271,7 +271,7 @@ abstract class QueryTest extends DatabaseTestCase
         $this->assertEquals(['team', 'company', 'age'], $query->groupBy);
     }
 
-    public function testHaving()
+    public function testHaving(): void
     {
         $query = new Query();
         $query->having('id = :id', [':id' => 1]);
@@ -287,7 +287,7 @@ abstract class QueryTest extends DatabaseTestCase
         $this->assertEquals([':id' => 1, ':name' => 'something', ':age' => '30'], $query->params);
     }
 
-    public function testOrder()
+    public function testOrder(): void
     {
         $query = new Query();
         $query->orderBy('team');
@@ -314,7 +314,7 @@ abstract class QueryTest extends DatabaseTestCase
         $this->assertEquals([$expression, $expression], $query->orderBy);
     }
 
-    public function testLimitOffset()
+    public function testLimitOffset(): void
     {
         $query = new Query();
         $query->limit(10)->offset(5);
@@ -322,7 +322,7 @@ abstract class QueryTest extends DatabaseTestCase
         $this->assertEquals(5, $query->offset);
     }
 
-    public function testLimitOffsetWithExpression()
+    public function testLimitOffsetWithExpression(): void
     {
         $query = (new Query())->from('customer')->select('id')->orderBy('id');
         $query
@@ -337,7 +337,7 @@ abstract class QueryTest extends DatabaseTestCase
         $this->assertEquals([2, 3], $result);
     }
 
-    public function testUnion()
+    public function testUnion(): void
     {
         $connection = $this->getConnection();
         $query = (new Query())
@@ -355,7 +355,7 @@ abstract class QueryTest extends DatabaseTestCase
         $this->assertCount(4, $result);
     }
 
-    public function testOne()
+    public function testOne(): void
     {
         $db = $this->getConnection();
 
@@ -366,7 +366,7 @@ abstract class QueryTest extends DatabaseTestCase
         $this->assertFalse($result);
     }
 
-    public function testExists()
+    public function testExists(): void
     {
         $db = $this->getConnection();
 
@@ -377,7 +377,7 @@ abstract class QueryTest extends DatabaseTestCase
         $this->assertFalse($result);
     }
 
-    public function testColumn()
+    public function testColumn(): void
     {
         $db = $this->getConnection();
         $result = (new Query())->select('name')->from('customer')->orderBy(['id' => SORT_DESC])->column($db);
@@ -422,7 +422,7 @@ abstract class QueryTest extends DatabaseTestCase
      *
      * @see https://github.com/yiisoft/yii2/issues/13859
      */
-    public function testAmbiguousColumnIndexBy()
+    public function testAmbiguousColumnIndexBy(): void
     {
         switch ($this->driverName) {
             case 'pgsql':
@@ -447,7 +447,7 @@ abstract class QueryTest extends DatabaseTestCase
         ], $result);
     }
 
-    public function testCount()
+    public function testCount(): void
     {
         $db = $this->getConnection();
 
@@ -472,7 +472,7 @@ abstract class QueryTest extends DatabaseTestCase
      * @depends testFilterWhereWithHashFormat
      * @depends testFilterWhereWithOperatorFormat
      */
-    public function testAndFilterCompare()
+    public function testAndFilterCompare(): void
     {
         $query = new Query();
 
@@ -505,7 +505,7 @@ abstract class QueryTest extends DatabaseTestCase
      *
      * @depends testCount
      */
-    public function testCountHavingWithoutGroupBy()
+    public function testCountHavingWithoutGroupBy(): void
     {
         if (!\in_array($this->driverName, ['mysql'])) {
             $this->markTestSkipped("{$this->driverName} does not support having without group by.");
@@ -517,7 +517,7 @@ abstract class QueryTest extends DatabaseTestCase
         $this->assertEquals(1, $count);
     }
 
-    public function testEmulateExecution()
+    public function testEmulateExecution(): void
     {
         $db = $this->getConnection();
 
@@ -614,7 +614,7 @@ abstract class QueryTest extends DatabaseTestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/13745
      */
-    public function testMultipleLikeConditions()
+    public function testMultipleLikeConditions(): void
     {
         $db = $this->getConnection();
         $tableName = 'like_test';
@@ -660,12 +660,12 @@ abstract class QueryTest extends DatabaseTestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/15355
      */
-    public function testExpressionInFrom()
+    public function testExpressionInFrom(): void
     {
         $db = $this->getConnection();
         $query = (new Query())
             ->from(
-                new \yii\db\Expression(
+                new Expression(
                     '(SELECT [[id]], [[name]], [[email]], [[address]], [[status]] FROM {{customer}}) c'
                 )
             )
@@ -675,7 +675,7 @@ abstract class QueryTest extends DatabaseTestCase
         $this->assertEquals('user3', $result['name']);
     }
 
-    public function testQueryCache()
+    public function testQueryCache(): void
     {
         $db = $this->getConnection();
         $db->enableQueryCache = true;
@@ -736,7 +736,7 @@ abstract class QueryTest extends DatabaseTestCase
     /**
      * checks that all needed properties copied from source to new query
      */
-    public function testQueryCreation()
+    public function testQueryCreation(): void
     {
         $where = 'id > :min_user_id';
         $limit = 50;
diff --git a/tests/framework/db/SchemaTest.php b/tests/framework/db/SchemaTest.php
index 366f5c4170..86526410ae 100644
--- a/tests/framework/db/SchemaTest.php
+++ b/tests/framework/db/SchemaTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\db;
 
+use Exception;
 use PDO;
 use yii\caching\ArrayCache;
 use yii\caching\FileCache;
@@ -35,7 +36,7 @@ abstract class SchemaTest extends DatabaseTestCase
         ];
     }
 
-    public function testGetSchemaNames()
+    public function testGetSchemaNames(): void
     {
         /** @var Schema $schema */
         $schema = $this->getConnection()->schema;
@@ -51,7 +52,7 @@ abstract class SchemaTest extends DatabaseTestCase
      * @dataProvider pdoAttributesProvider
      * @param array $pdoAttributes
      */
-    public function testGetTableNames($pdoAttributes)
+    public function testGetTableNames($pdoAttributes): void
     {
         $connection = $this->getConnection();
         foreach ($pdoAttributes as $name => $value) {
@@ -84,7 +85,7 @@ abstract class SchemaTest extends DatabaseTestCase
      * @dataProvider pdoAttributesProvider
      * @param array $pdoAttributes
      */
-    public function testGetTableSchemas($pdoAttributes)
+    public function testGetTableSchemas($pdoAttributes): void
     {
         $connection = $this->getConnection();
         foreach ($pdoAttributes as $name => $value) {
@@ -103,22 +104,22 @@ abstract class SchemaTest extends DatabaseTestCase
         }
     }
 
-    public function testGetTableSchemasWithAttrCase()
+    public function testGetTableSchemasWithAttrCase(): void
     {
         $db = $this->getConnection(false);
-        $db->slavePdo->setAttribute(\PDO::ATTR_CASE, \PDO::CASE_LOWER);
+        $db->slavePdo->setAttribute(PDO::ATTR_CASE, PDO::CASE_LOWER);
         $this->assertEquals(\count($db->schema->getTableNames()), \count($db->schema->getTableSchemas()));
 
-        $db->slavePdo->setAttribute(\PDO::ATTR_CASE, \PDO::CASE_UPPER);
+        $db->slavePdo->setAttribute(PDO::ATTR_CASE, PDO::CASE_UPPER);
         $this->assertEquals(\count($db->schema->getTableNames()), \count($db->schema->getTableSchemas()));
     }
 
-    public function testGetNonExistingTableSchema()
+    public function testGetNonExistingTableSchema(): void
     {
         $this->assertNull($this->getConnection()->schema->getTableSchema('nonexisting_table'));
     }
 
-    public function testSchemaCache()
+    public function testSchemaCache(): void
     {
         /** @var Connection $db */
         $db = $this->getConnection();
@@ -142,7 +143,7 @@ abstract class SchemaTest extends DatabaseTestCase
     /**
      * @depends testSchemaCache
      */
-    public function testRefreshTableSchema()
+    public function testRefreshTableSchema(): void
     {
         /** @var Schema $schema */
         $schema = $this->getConnection()->schema;
@@ -201,7 +202,7 @@ abstract class SchemaTest extends DatabaseTestCase
      * @dataProvider tableSchemaCachePrefixesProvider
      * @depends      testSchemaCache
      */
-    public function testTableSchemaCacheWithTablePrefixes($tablePrefix, $tableName, $testTablePrefix, $testTableName)
+    public function testTableSchemaCacheWithTablePrefixes($tablePrefix, $tableName, $testTablePrefix, $testTableName): void
     {
         /** @var Schema $schema */
         $schema = $this->getConnection()->schema;
@@ -232,7 +233,7 @@ abstract class SchemaTest extends DatabaseTestCase
         $this->assertNotSame($testNoCacheTable, $testRefreshedTable);
     }
 
-    public function testCompositeFk()
+    public function testCompositeFk(): void
     {
         /** @var Schema $schema */
         $schema = $this->getConnection()->schema;
@@ -246,18 +247,18 @@ abstract class SchemaTest extends DatabaseTestCase
         $this->assertEquals('item_id', $table->foreignKeys['FK_composite_fk_order_item']['item_id']);
     }
 
-    public function testGetPDOType()
+    public function testGetPDOType(): void
     {
         $values = [
-            [null, \PDO::PARAM_NULL],
-            ['', \PDO::PARAM_STR],
-            ['hello', \PDO::PARAM_STR],
-            [0, \PDO::PARAM_INT],
-            [1, \PDO::PARAM_INT],
-            [1337, \PDO::PARAM_INT],
-            [true, \PDO::PARAM_BOOL],
-            [false, \PDO::PARAM_BOOL],
-            [$fp = fopen(__FILE__, 'rb'), \PDO::PARAM_LOB],
+            [null, PDO::PARAM_NULL],
+            ['', PDO::PARAM_STR],
+            ['hello', PDO::PARAM_STR],
+            [0, PDO::PARAM_INT],
+            [1, PDO::PARAM_INT],
+            [1337, PDO::PARAM_INT],
+            [true, PDO::PARAM_BOOL],
+            [false, PDO::PARAM_BOOL],
+            [$fp = fopen(__FILE__, 'rb'), PDO::PARAM_LOB],
         ];
 
         /** @var Schema $schema */
@@ -491,7 +492,7 @@ abstract class SchemaTest extends DatabaseTestCase
         ];
     }
 
-    public function testNegativeDefaultValues()
+    public function testNegativeDefaultValues(): void
     {
         /** @var Schema $schema */
         $schema = $this->getConnection()->schema;
@@ -505,7 +506,7 @@ abstract class SchemaTest extends DatabaseTestCase
         $this->assertEquals(-33.22, $table->getColumn('numeric_col')->defaultValue);
     }
 
-    public function testColumnSchema()
+    public function testColumnSchema(): void
     {
         $columns = $this->getExpectedColumns();
 
@@ -540,7 +541,7 @@ abstract class SchemaTest extends DatabaseTestCase
         }
     }
 
-    public function testColumnSchemaDbTypecastWithEmptyCharType()
+    public function testColumnSchemaDbTypecastWithEmptyCharType(): void
     {
         $columnSchema = new ColumnSchema(['type' => Schema::TYPE_CHAR]);
         $this->assertSame('', $columnSchema->dbTypecast(''));
@@ -551,7 +552,7 @@ abstract class SchemaTest extends DatabaseTestCase
      * @param mixed $value
      * @param bool $expected
      */
-    public function testColumnSchemaDbTypecastBooleanPhpType($value, $expected)
+    public function testColumnSchemaDbTypecastBooleanPhpType($value, $expected): void
     {
         $columnSchema = new ColumnSchema(['phpType' => Schema::TYPE_BOOLEAN]);
         $this->assertSame($expected, $columnSchema->dbTypecast($value));
@@ -579,7 +580,7 @@ abstract class SchemaTest extends DatabaseTestCase
         ];
     }
 
-    public function testFindUniqueIndexes()
+    public function testFindUniqueIndexes(): void
     {
         if ($this->driverName === 'sqlsrv') {
             $this->markTestSkipped('`\yii\db\mssql\Schema::findUniqueIndexes()` returns only unique constraints not unique indexes.');
@@ -589,7 +590,7 @@ abstract class SchemaTest extends DatabaseTestCase
 
         try {
             $db->createCommand()->dropTable('uniqueIndex')->execute();
-        } catch (\Exception $e) {
+        } catch (Exception $e) {
         }
         $db->createCommand()->createTable('uniqueIndex', [
             'somecol' => 'string',
@@ -630,7 +631,7 @@ abstract class SchemaTest extends DatabaseTestCase
         ], $uniqueIndexes);
     }
 
-    public function testContraintTablesExistance()
+    public function testContraintTablesExistance(): void
     {
         $tableNames = [
             'T_constraints_1',
@@ -768,7 +769,7 @@ abstract class SchemaTest extends DatabaseTestCase
      * @param string $type
      * @param mixed $expected
      */
-    public function testTableSchemaConstraints($tableName, $type, $expected)
+    public function testTableSchemaConstraints($tableName, $type, $expected): void
     {
         if ($expected === false) {
             $this->expectException('yii\base\NotSupportedException');
@@ -784,7 +785,7 @@ abstract class SchemaTest extends DatabaseTestCase
      * @param string $type
      * @param mixed $expected
      */
-    public function testTableSchemaConstraintsWithPdoUppercase($tableName, $type, $expected)
+    public function testTableSchemaConstraintsWithPdoUppercase($tableName, $type, $expected): void
     {
         if ($expected === false) {
             $this->expectException('yii\base\NotSupportedException');
@@ -802,7 +803,7 @@ abstract class SchemaTest extends DatabaseTestCase
      * @param string $type
      * @param mixed $expected
      */
-    public function testTableSchemaConstraintsWithPdoLowercase($tableName, $type, $expected)
+    public function testTableSchemaConstraintsWithPdoLowercase($tableName, $type, $expected): void
     {
         if ($expected === false) {
             $this->expectException('yii\base\NotSupportedException');
diff --git a/tests/framework/db/cubrid/CommandTest.php b/tests/framework/db/cubrid/CommandTest.php
index 1a273e8ba7..29b2add60f 100644
--- a/tests/framework/db/cubrid/CommandTest.php
+++ b/tests/framework/db/cubrid/CommandTest.php
@@ -16,7 +16,7 @@ class CommandTest extends \yiiunit\framework\db\CommandTest
 {
     public $driverName = 'cubrid';
 
-    public function testBindParamValue()
+    public function testBindParamValue(): void
     {
         $db = $this->getConnection();
 
@@ -76,7 +76,7 @@ class CommandTest extends \yiiunit\framework\db\CommandTest
         $this->assertEquals('user5@example.com', $command->queryScalar());
     }
 
-    public function testAutoQuoting()
+    public function testAutoQuoting(): void
     {
         $db = $this->getConnection(false);
 
@@ -94,7 +94,7 @@ class CommandTest extends \yiiunit\framework\db\CommandTest
         return $data;
     }
 
-    public function testAddDropCheck()
+    public function testAddDropCheck(): void
     {
         $this->markTestSkipped('CUBRID does not support adding/dropping check constraints.');
     }
diff --git a/tests/framework/db/cubrid/ConnectionTest.php b/tests/framework/db/cubrid/ConnectionTest.php
index 5a05cdab12..1ce9af0616 100644
--- a/tests/framework/db/cubrid/ConnectionTest.php
+++ b/tests/framework/db/cubrid/ConnectionTest.php
@@ -16,7 +16,7 @@ class ConnectionTest extends \yiiunit\framework\db\ConnectionTest
 {
     public $driverName = 'cubrid';
 
-    public function testQuoteValue()
+    public function testQuoteValue(): void
     {
         $connection = $this->getConnection(false);
         $this->assertEquals(123, $connection->quoteValue(123));
@@ -24,7 +24,7 @@ class ConnectionTest extends \yiiunit\framework\db\ConnectionTest
         $this->assertEquals("'It''s interesting'", $connection->quoteValue("It's interesting"));
     }
 
-    public function testQuoteTableName()
+    public function testQuoteTableName(): void
     {
         $connection = $this->getConnection(false);
         $this->assertEquals('"table"', $connection->quoteTableName('table'));
@@ -36,7 +36,7 @@ class ConnectionTest extends \yiiunit\framework\db\ConnectionTest
         $this->assertEquals('(table)', $connection->quoteTableName('(table)'));
     }
 
-    public function testQuoteColumnName()
+    public function testQuoteColumnName(): void
     {
         $connection = $this->getConnection(false);
         $this->assertEquals('"column"', $connection->quoteColumnName('column'));
@@ -49,7 +49,7 @@ class ConnectionTest extends \yiiunit\framework\db\ConnectionTest
         $this->assertEquals('"column"', $connection->quoteSql('{{column}}'));
     }
 
-    public function testQuoteFullColumnName()
+    public function testQuoteFullColumnName(): void
     {
         $connection = $this->getConnection(false, false);
         $this->assertEquals('"table"."column"', $connection->quoteColumnName('table.column'));
diff --git a/tests/framework/db/cubrid/QueryBuilderTest.php b/tests/framework/db/cubrid/QueryBuilderTest.php
index dd1b7f94e7..ee0a30476b 100644
--- a/tests/framework/db/cubrid/QueryBuilderTest.php
+++ b/tests/framework/db/cubrid/QueryBuilderTest.php
@@ -8,6 +8,8 @@
 
 namespace yiiunit\framework\db\cubrid;
 
+use PDO;
+
 /**
  * @group db
  * @group cubrid
@@ -33,17 +35,17 @@ class QueryBuilderTest extends \yiiunit\framework\db\QueryBuilderTest
         return array_merge(parent::columnTypes(), []);
     }
 
-    public function checksProvider()
+    public function checksProvider(): void
     {
         $this->markTestSkipped('Adding/dropping check constraints is not supported in CUBRID.');
     }
 
-    public function defaultValuesProvider()
+    public function defaultValuesProvider(): void
     {
         $this->markTestSkipped('Adding/dropping default constraints is not supported in CUBRID.');
     }
 
-    public function testResetSequence()
+    public function testResetSequence(): void
     {
         $qb = $this->getQueryBuilder();
 
@@ -56,9 +58,9 @@ class QueryBuilderTest extends \yiiunit\framework\db\QueryBuilderTest
         $this->assertEquals($expected, $sql);
     }
 
-    public function testCommentColumn()
+    public function testCommentColumn(): void
     {
-        $version = $this->getQueryBuilder(false)->db->getSlavePdo(true)->getAttribute(\PDO::ATTR_SERVER_VERSION);
+        $version = $this->getQueryBuilder(false)->db->getSlavePdo(true)->getAttribute(PDO::ATTR_SERVER_VERSION);
         if (version_compare($version, '10.0', '<')) {
             $this->markTestSkipped('Comments on columns are supported starting with CUBRID 10.0.');
             return;
diff --git a/tests/framework/db/cubrid/SchemaTest.php b/tests/framework/db/cubrid/SchemaTest.php
index ac0a2dc7d5..23f9a374f9 100644
--- a/tests/framework/db/cubrid/SchemaTest.php
+++ b/tests/framework/db/cubrid/SchemaTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\db\cubrid;
 
+use PDO;
 use yii\db\Expression;
 use yiiunit\framework\db\AnyCaseValue;
 
@@ -19,23 +20,23 @@ class SchemaTest extends \yiiunit\framework\db\SchemaTest
 {
     public $driverName = 'cubrid';
 
-    public function testGetSchemaNames()
+    public function testGetSchemaNames(): void
     {
         $this->markTestSkipped('Schemas are not supported in CUBRID.');
     }
 
-    public function testGetPDOType()
+    public function testGetPDOType(): void
     {
         $values = [
-            [null, \PDO::PARAM_NULL],
-            ['', \PDO::PARAM_STR],
-            ['hello', \PDO::PARAM_STR],
-            [0, \PDO::PARAM_INT],
-            [1, \PDO::PARAM_INT],
-            [1337, \PDO::PARAM_INT],
-            [true, \PDO::PARAM_INT],
-            [false, \PDO::PARAM_INT],
-            [$fp = fopen(__FILE__, 'rb'), \PDO::PARAM_LOB],
+            [null, PDO::PARAM_NULL],
+            ['', PDO::PARAM_STR],
+            ['hello', PDO::PARAM_STR],
+            [0, PDO::PARAM_INT],
+            [1, PDO::PARAM_INT],
+            [1337, PDO::PARAM_INT],
+            [true, PDO::PARAM_INT],
+            [false, PDO::PARAM_INT],
+            [$fp = fopen(__FILE__, 'rb'), PDO::PARAM_LOB],
         ];
 
         $schema = $this->getConnection()->schema;
@@ -107,12 +108,12 @@ class SchemaTest extends \yiiunit\framework\db\SchemaTest
         return $result;
     }
 
-    public function lowercaseConstraintsProvider()
+    public function lowercaseConstraintsProvider(): void
     {
         $this->markTestSkipped('This test hangs on CUBRID.');
     }
 
-    public function uppercaseConstraintsProvider()
+    public function uppercaseConstraintsProvider(): void
     {
         $this->markTestSkipped('This test hangs on CUBRID.');
     }
diff --git a/tests/framework/db/mssql/ActiveRecordTest.php b/tests/framework/db/mssql/ActiveRecordTest.php
index 43bcfa5a65..ccb2b15065 100644
--- a/tests/framework/db/mssql/ActiveRecordTest.php
+++ b/tests/framework/db/mssql/ActiveRecordTest.php
@@ -22,12 +22,12 @@ class ActiveRecordTest extends \yiiunit\framework\db\ActiveRecordTest
 {
     public $driverName = 'sqlsrv';
 
-    public function testExplicitPkOnAutoIncrement()
+    public function testExplicitPkOnAutoIncrement(): void
     {
         $this->markTestSkipped('MSSQL does not support explicit value for an IDENTITY column.');
     }
 
-    public function testCastValues()
+    public function testCastValues(): void
     {
         $model = new Type();
         $model->int_col = 123;
@@ -59,7 +59,7 @@ class ActiveRecordTest extends \yiiunit\framework\db\ActiveRecordTest
     /**
      * @throws Exception
      */
-    public function testSaveWithTrigger()
+    public function testSaveWithTrigger(): void
     {
         $db = $this->getConnection();
 
@@ -93,7 +93,7 @@ END';
     /**
      * @throws Exception
      */
-    public function testSaveWithComputedColumn()
+    public function testSaveWithComputedColumn(): void
     {
         $db = $this->getConnection();
 
@@ -120,7 +120,7 @@ END';
     /**
      * @throws Exception
      */
-    public function testSaveWithRowVersionColumn()
+    public function testSaveWithRowVersionColumn(): void
     {
         $db = $this->getConnection();
 
@@ -137,7 +137,7 @@ END';
     /**
      * @throws Exception
      */
-    public function testSaveWithRowVersionNullColumn()
+    public function testSaveWithRowVersionNullColumn(): void
     {
         $db = $this->getConnection();
 
diff --git a/tests/framework/db/mssql/CommandTest.php b/tests/framework/db/mssql/CommandTest.php
index 82f61073c7..f161c9c001 100644
--- a/tests/framework/db/mssql/CommandTest.php
+++ b/tests/framework/db/mssql/CommandTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\db\mssql;
 
+use yii\db\pgsql\Schema;
 use yii\db\Query;
 
 /**
@@ -18,7 +19,7 @@ class CommandTest extends \yiiunit\framework\db\CommandTest
 {
     protected $driverName = 'sqlsrv';
 
-    public function testAutoQuoting()
+    public function testAutoQuoting(): void
     {
         $db = $this->getConnection(false);
 
@@ -27,12 +28,12 @@ class CommandTest extends \yiiunit\framework\db\CommandTest
         $this->assertEquals('SELECT [id], [t].[name] FROM [customer] t', $command->sql);
     }
 
-    public function testPrepareCancel()
+    public function testPrepareCancel(): void
     {
         $this->markTestSkipped('MSSQL driver does not support this feature.');
     }
 
-    public function testBindParamValue()
+    public function testBindParamValue(): void
     {
         $db = $this->getConnection();
 
@@ -98,12 +99,12 @@ class CommandTest extends \yiiunit\framework\db\CommandTest
         ];
     }
 
-    public function testAddDropDefaultValue()
+    public function testAddDropDefaultValue(): void
     {
         $db = $this->getConnection(false);
         $tableName = 'test_def';
         $name = 'test_def_constraint';
-        /** @var \yii\db\pgsql\Schema $schema */
+        /** @var Schema $schema */
         $schema = $db->getSchema();
 
         if ($schema->getTableSchema($tableName) !== null) {
@@ -132,7 +133,7 @@ class CommandTest extends \yiiunit\framework\db\CommandTest
         return $data;
     }
 
-    public function testUpsertVarbinary()
+    public function testUpsertVarbinary(): void
     {
         $db = $this->getConnection();
 
diff --git a/tests/framework/db/mssql/ConnectionTest.php b/tests/framework/db/mssql/ConnectionTest.php
index 4b78a36875..bb00efc63d 100644
--- a/tests/framework/db/mssql/ConnectionTest.php
+++ b/tests/framework/db/mssql/ConnectionTest.php
@@ -16,7 +16,7 @@ class ConnectionTest extends \yiiunit\framework\db\ConnectionTest
 {
     protected $driverName = 'sqlsrv';
 
-    public function testQuoteValue()
+    public function testQuoteValue(): void
     {
         $connection = $this->getConnection(false);
         $this->assertEquals(123, $connection->quoteValue(123));
@@ -24,7 +24,7 @@ class ConnectionTest extends \yiiunit\framework\db\ConnectionTest
         $this->assertEquals("'It''s interesting'", $connection->quoteValue("It's interesting"));
     }
 
-    public function testQuoteTableName()
+    public function testQuoteTableName(): void
     {
         $connection = $this->getConnection(false);
         $this->assertEquals('[table]', $connection->quoteTableName('table'));
@@ -36,7 +36,7 @@ class ConnectionTest extends \yiiunit\framework\db\ConnectionTest
         $this->assertEquals('(table)', $connection->quoteTableName('(table)'));
     }
 
-    public function testQuoteColumnName()
+    public function testQuoteColumnName(): void
     {
         $connection = $this->getConnection(false);
         $this->assertEquals('[column]', $connection->quoteColumnName('column'));
@@ -49,7 +49,7 @@ class ConnectionTest extends \yiiunit\framework\db\ConnectionTest
         $this->assertEquals('[column]', $connection->quoteSql('{{column}}'));
     }
 
-    public function testQuoteFullColumnName()
+    public function testQuoteFullColumnName(): void
     {
         $connection = $this->getConnection(false, false);
         $this->assertEquals('[table].[column]', $connection->quoteColumnName('table.column'));
diff --git a/tests/framework/db/mssql/QueryBuilderTest.php b/tests/framework/db/mssql/QueryBuilderTest.php
index 8c585ce8c9..285e90d4b3 100644
--- a/tests/framework/db/mssql/QueryBuilderTest.php
+++ b/tests/framework/db/mssql/QueryBuilderTest.php
@@ -28,7 +28,7 @@ class QueryBuilderTest extends \yiiunit\framework\db\QueryBuilderTest
         '\\\\' => '[\\]',
     ];
 
-    public function testOffsetLimit()
+    public function testOffsetLimit(): void
     {
         $expectedQuerySql = 'SELECT [id] FROM [example] ORDER BY (SELECT NULL) OFFSET 5 ROWS FETCH NEXT 10 ROWS ONLY';
         $expectedQueryParams = [];
@@ -42,7 +42,7 @@ class QueryBuilderTest extends \yiiunit\framework\db\QueryBuilderTest
         $this->assertEquals($expectedQueryParams, $actualQueryParams);
     }
 
-    public function testLimit()
+    public function testLimit(): void
     {
         $expectedQuerySql = 'SELECT [id] FROM [example] ORDER BY (SELECT NULL) OFFSET 0 ROWS FETCH NEXT 10 ROWS ONLY';
         $expectedQueryParams = [];
@@ -56,7 +56,7 @@ class QueryBuilderTest extends \yiiunit\framework\db\QueryBuilderTest
         $this->assertEquals($expectedQueryParams, $actualQueryParams);
     }
 
-    public function testOffset()
+    public function testOffset(): void
     {
         $expectedQuerySql = 'SELECT [id] FROM [example] ORDER BY (SELECT NULL) OFFSET 10 ROWS';
         $expectedQueryParams = [];
@@ -128,7 +128,7 @@ class QueryBuilderTest extends \yiiunit\framework\db\QueryBuilderTest
         return $db->createCommand($sql)->execute();
     }
 
-    public function testCommentAdditionOnTableAndOnColumn()
+    public function testCommentAdditionOnTableAndOnColumn(): void
     {
         $table = 'profile';
         $tableComment = 'A comment for profile table.';
@@ -175,7 +175,7 @@ class QueryBuilderTest extends \yiiunit\framework\db\QueryBuilderTest
         ], $result[0]);
     }
 
-    public function testCommentAdditionOnQuotedTableOrColumn()
+    public function testCommentAdditionOnQuotedTableOrColumn(): void
     {
         $table = 'stranger \'table';
         $tableComment = 'A comment for stranger \'table.';
@@ -200,7 +200,7 @@ class QueryBuilderTest extends \yiiunit\framework\db\QueryBuilderTest
         ], $resultColumn[0]);
     }
 
-    public function testCommentRemovalFromTableAndFromColumn()
+    public function testCommentRemovalFromTableAndFromColumn(): void
     {
         $table = 'profile';
         $tableComment = 'A comment for profile table.';
@@ -217,7 +217,7 @@ class QueryBuilderTest extends \yiiunit\framework\db\QueryBuilderTest
         $this->assertEquals([], $result);
     }
 
-    public function testCommentRemovalFromQuotedTableOrColumn()
+    public function testCommentRemovalFromQuotedTableOrColumn(): void
     {
         $table = 'stranger \'table';
         $tableComment = 'A comment for stranger \'table.';
@@ -234,12 +234,12 @@ class QueryBuilderTest extends \yiiunit\framework\db\QueryBuilderTest
         $this->assertEquals([], $result);
     }
 
-    public function testCommentColumn()
+    public function testCommentColumn(): void
     {
         $this->markTestSkipped('Testing the behavior, not sql generation anymore.');
     }
 
-    public function testCommentTable()
+    public function testCommentTable(): void
     {
         $this->markTestSkipped('Testing the behavior, not sql generation anymore.');
     }
@@ -361,7 +361,7 @@ class QueryBuilderTest extends \yiiunit\framework\db\QueryBuilderTest
         ];
     }
 
-    public function testResetSequence()
+    public function testResetSequence(): void
     {
         $qb = $this->getQueryBuilder();
 
@@ -447,7 +447,7 @@ class QueryBuilderTest extends \yiiunit\framework\db\QueryBuilderTest
         return $data;
     }
 
-    public function testAlterColumn()
+    public function testAlterColumn(): void
     {
         $qb = $this->getQueryBuilder();
 
@@ -639,7 +639,7 @@ ALTER TABLE [foo1] ADD CONSTRAINT [UQ_foo1_bar] UNIQUE ([bar])";
         $this->assertEquals($expected, $sql);
     }
 
-    public function testAlterColumnOnDb()
+    public function testAlterColumnOnDb(): void
     {
         $connection = $this->getConnection();
 
@@ -657,7 +657,7 @@ ALTER TABLE [foo1] ADD CONSTRAINT [UQ_foo1_bar] UNIQUE ([bar])";
         $this->assertEquals(false, $schema->getColumn('bar')->allowNull);
     }
 
-    public function testAlterColumnWithNull()
+    public function testAlterColumnWithNull(): void
     {
         $qb = $this->getQueryBuilder();
 
@@ -689,7 +689,7 @@ ALTER TABLE [foo1] ADD CONSTRAINT [DF_foo1_bar] DEFAULT NULL FOR [bar]";
         $this->assertEquals($expected, $sql);
     }
 
-    public function testAlterColumnWithExpression()
+    public function testAlterColumnWithExpression(): void
     {
         $qb = $this->getQueryBuilder();
 
@@ -721,7 +721,7 @@ ALTER TABLE [foo1] ADD CONSTRAINT [DF_foo1_bar] DEFAULT CAST(GETDATE() AS INT) F
         $this->assertEquals($expected, $sql);
     }
 
-    public function testAlterColumnWithCheckConstraintOnDb()
+    public function testAlterColumnWithCheckConstraintOnDb(): void
     {
         $connection = $this->getConnection();
 
@@ -735,7 +735,7 @@ ALTER TABLE [foo1] ADD CONSTRAINT [DF_foo1_bar] DEFAULT CAST(GETDATE() AS INT) F
         $this->assertEquals(1, $connection->createCommand($sql)->execute());
     }
 
-    public function testAlterColumnWithCheckConstraintOnDbWithException()
+    public function testAlterColumnWithCheckConstraintOnDbWithException(): void
     {
         $connection = $this->getConnection();
 
@@ -747,7 +747,7 @@ ALTER TABLE [foo1] ADD CONSTRAINT [DF_foo1_bar] DEFAULT CAST(GETDATE() AS INT) F
         $this->assertEquals(1, $connection->createCommand($sql)->execute());
     }
 
-    public function testAlterColumnWithUniqueConstraintOnDbWithException()
+    public function testAlterColumnWithUniqueConstraintOnDbWithException(): void
     {
         $connection = $this->getConnection();
 
@@ -761,7 +761,7 @@ ALTER TABLE [foo1] ADD CONSTRAINT [DF_foo1_bar] DEFAULT CAST(GETDATE() AS INT) F
         $this->assertEquals(1, $connection->createCommand($sql)->execute());
     }
 
-    public function testDropColumn()
+    public function testDropColumn(): void
     {
         $qb = $this->getQueryBuilder();
 
@@ -792,7 +792,7 @@ ALTER TABLE [foo1] DROP COLUMN [bar]";
         $this->assertEquals($expected, $sql);
     }
 
-    public function testDropColumnOnDb()
+    public function testDropColumnOnDb(): void
     {
         $connection = $this->getConnection();
 
diff --git a/tests/framework/db/mssql/QueryCacheTest.php b/tests/framework/db/mssql/QueryCacheTest.php
index 78fcbb012e..01f0a3fb30 100644
--- a/tests/framework/db/mssql/QueryCacheTest.php
+++ b/tests/framework/db/mssql/QueryCacheTest.php
@@ -20,7 +20,7 @@ class QueryCacheTest extends DatabaseTestCase
 {
     protected $driverName = 'sqlsrv';
 
-    public function testQueryCacheFileCache()
+    public function testQueryCacheFileCache(): void
     {
         $db = $this->getConnection();
         $db->enableQueryCache = true;
diff --git a/tests/framework/db/mssql/QueryTest.php b/tests/framework/db/mssql/QueryTest.php
index 3f4de9b733..9fe5c445e6 100644
--- a/tests/framework/db/mssql/QueryTest.php
+++ b/tests/framework/db/mssql/QueryTest.php
@@ -18,7 +18,7 @@ class QueryTest extends \yiiunit\framework\db\QueryTest
 {
     protected $driverName = 'sqlsrv';
 
-    public function testUnion()
+    public function testUnion(): void
     {
         $connection = $this->getConnection();
 
diff --git a/tests/framework/db/mssql/SchemaTest.php b/tests/framework/db/mssql/SchemaTest.php
index 3a45bf8637..0414abaad5 100644
--- a/tests/framework/db/mssql/SchemaTest.php
+++ b/tests/framework/db/mssql/SchemaTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\db\mssql;
 
+use yii\base\NotSupportedException;
 use yii\db\DefaultValueConstraint;
 use yii\db\mssql\Schema;
 use yiiunit\framework\db\AnyValue;
@@ -45,7 +46,7 @@ class SchemaTest extends \yiiunit\framework\db\SchemaTest
         return $result;
     }
 
-    public function testGetStringFieldsSize()
+    public function testGetStringFieldsSize(): void
     {
         /** @var Connection $db */
         $db = $this->getConnection();
@@ -90,9 +91,9 @@ class SchemaTest extends \yiiunit\framework\db\SchemaTest
      * @dataProvider quoteTableNameDataProvider
      * @param $name
      * @param $expectedName
-     * @throws \yii\base\NotSupportedException
+     * @throws NotSupportedException
      */
-    public function testQuoteTableName($name, $expectedName)
+    public function testQuoteTableName($name, $expectedName): void
     {
         $schema = $this->getConnection()->getSchema();
         $quotedName = $schema->quoteTableName($name);
@@ -117,9 +118,9 @@ class SchemaTest extends \yiiunit\framework\db\SchemaTest
      * @dataProvider getTableSchemaDataProvider
      * @param $name
      * @param $expectedName
-     * @throws \yii\base\NotSupportedException
+     * @throws NotSupportedException
      */
-    public function testGetTableSchema($name, $expectedName)
+    public function testGetTableSchema($name, $expectedName): void
     {
         $schema = $this->getConnection()->getSchema();
         $tableSchema = $schema->getTableSchema($name);
@@ -183,7 +184,7 @@ class SchemaTest extends \yiiunit\framework\db\SchemaTest
         return $columns;
     }
 
-    public function testGetPrimaryKey()
+    public function testGetPrimaryKey(): void
     {
         $db = $this->getConnection();
 
diff --git a/tests/framework/db/mssql/type/BooleanTest.php b/tests/framework/db/mssql/type/BooleanTest.php
index 26d3af23d1..01aa035e7f 100644
--- a/tests/framework/db/mssql/type/BooleanTest.php
+++ b/tests/framework/db/mssql/type/BooleanTest.php
@@ -19,7 +19,7 @@ class BooleanTest extends DatabaseTestCase
 {
     protected $driverName = 'sqlsrv';
 
-    public function testBoolean()
+    public function testBoolean(): void
     {
         $db = $this->getConnection(true);
         $schema = $db->getSchema();
@@ -60,7 +60,7 @@ class BooleanTest extends DatabaseTestCase
         $this->assertTrue($phpTypeCast);
     }
 
-    public function testBooleanWithValueInteger()
+    public function testBooleanWithValueInteger(): void
     {
         $db = $this->getConnection(true);
         $schema = $db->getSchema();
@@ -101,7 +101,7 @@ class BooleanTest extends DatabaseTestCase
         $this->assertTrue($phpTypeCast);
     }
 
-    public function testBooleanValueNegative()
+    public function testBooleanValueNegative(): void
     {
         $db = $this->getConnection(true);
         $schema = $db->getSchema();
@@ -133,7 +133,7 @@ class BooleanTest extends DatabaseTestCase
         $this->assertTrue($phpTypeCast);
     }
 
-    public function testBooleanWithValueNull()
+    public function testBooleanWithValueNull(): void
     {
         $db = $this->getConnection(true);
         $schema = $db->getSchema();
@@ -165,7 +165,7 @@ class BooleanTest extends DatabaseTestCase
         $this->assertNull($phpTypeCast);
     }
 
-    public function testBooleanWithValueOverflow()
+    public function testBooleanWithValueOverflow(): void
     {
         $db = $this->getConnection(true);
         $schema = $db->getSchema();
diff --git a/tests/framework/db/mssql/type/VarbinaryTest.php b/tests/framework/db/mssql/type/VarbinaryTest.php
index e3811b4330..b3f3eb6d1d 100644
--- a/tests/framework/db/mssql/type/VarbinaryTest.php
+++ b/tests/framework/db/mssql/type/VarbinaryTest.php
@@ -19,7 +19,7 @@ class VarbinaryTest extends DatabaseTestCase
 {
     protected $driverName = 'sqlsrv';
 
-    public function testVarbinary()
+    public function testVarbinary(): void
     {
         $db = $this->getConnection();
 
diff --git a/tests/framework/db/mysql/ActiveRecordTest.php b/tests/framework/db/mysql/ActiveRecordTest.php
index bbda237c45..1509a57fc9 100644
--- a/tests/framework/db/mysql/ActiveRecordTest.php
+++ b/tests/framework/db/mysql/ActiveRecordTest.php
@@ -19,7 +19,7 @@ class ActiveRecordTest extends \yiiunit\framework\db\ActiveRecordTest
 {
     public $driverName = 'mysql';
 
-    public function testCastValues()
+    public function testCastValues(): void
     {
         $model = new Type();
         $model->int_col = 123;
@@ -48,7 +48,7 @@ class ActiveRecordTest extends \yiiunit\framework\db\ActiveRecordTest
         //$this->assertSame(false, $model->bool_col2);
     }
 
-    public function testJsonColumn()
+    public function testJsonColumn(): void
     {
         if (version_compare($this->getConnection()->getSchema()->getServerVersion(), '5.7', '<')) {
             $this->markTestSkipped('JSON columns are not supported in MySQL < 5.7');
diff --git a/tests/framework/db/mysql/BaseActiveRecordTest.php b/tests/framework/db/mysql/BaseActiveRecordTest.php
index 8acdc27ac8..a6812ccd59 100644
--- a/tests/framework/db/mysql/BaseActiveRecordTest.php
+++ b/tests/framework/db/mysql/BaseActiveRecordTest.php
@@ -17,7 +17,7 @@ class BaseActiveRecordTest extends \yiiunit\framework\db\BaseActiveRecordTest
      *
      * @dataProvider provideArrayValueWithChange
      */
-    public function testJsonDirtyAttributesWithDataChange($actual, $modified)
+    public function testJsonDirtyAttributesWithDataChange($actual, $modified): void
     {
         if (version_compare($this->getConnection()->getSchema()->getServerVersion(), '5.7', '<')) {
             $this->markTestSkipped('JSON columns are not supported in MySQL < 5.7');
diff --git a/tests/framework/db/mysql/CommandTest.php b/tests/framework/db/mysql/CommandTest.php
index 498d0f1feb..f77f612260 100644
--- a/tests/framework/db/mysql/CommandTest.php
+++ b/tests/framework/db/mysql/CommandTest.php
@@ -18,7 +18,7 @@ class CommandTest extends \yiiunit\framework\db\CommandTest
 
     protected $upsertTestCharCast = 'CONVERT([[address]], CHAR)';
 
-    public function testAddDropCheckSeveral()
+    public function testAddDropCheckSeveral(): void
     {
         $db = $this->getConnection(false);
 
diff --git a/tests/framework/db/mysql/ConnectionTest.php b/tests/framework/db/mysql/ConnectionTest.php
index 8a700afa01..e4320d785c 100644
--- a/tests/framework/db/mysql/ConnectionTest.php
+++ b/tests/framework/db/mysql/ConnectionTest.php
@@ -21,7 +21,7 @@ class ConnectionTest extends \yiiunit\framework\db\ConnectionTest
     /**
      * @doesNotPerformAssertions
      */
-    public function testTransactionAutocommit()
+    public function testTransactionAutocommit(): void
     {
         /** @var Connection $connection */
         $connection = $this->getConnection(true);
diff --git a/tests/framework/db/mysql/QueryBuilderTest.php b/tests/framework/db/mysql/QueryBuilderTest.php
index 03455f0e0c..8ff9696a94 100644
--- a/tests/framework/db/mysql/QueryBuilderTest.php
+++ b/tests/framework/db/mysql/QueryBuilderTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\db\mysql;
 
+use PDO;
 use yii\base\DynamicModel;
 use yii\db\Expression;
 use yii\db\JsonExpression;
@@ -126,7 +127,7 @@ class QueryBuilderTest extends \yiiunit\framework\db\QueryBuilderTest
         /**
          * @link https://github.com/yiisoft/yii2/issues/14367
          */
-        $mysqlVersion = $this->getDb()->getSlavePdo(true)->getAttribute(\PDO::ATTR_SERVER_VERSION);
+        $mysqlVersion = $this->getDb()->getSlavePdo(true)->getAttribute(PDO::ATTR_SERVER_VERSION);
         $supportsFractionalSeconds = version_compare($mysqlVersion, '5.6.4', '>=');
         if ($supportsFractionalSeconds) {
             $expectedValues = [
@@ -197,12 +198,12 @@ class QueryBuilderTest extends \yiiunit\framework\db\QueryBuilderTest
         return $result;
     }
 
-    public function defaultValuesProvider()
+    public function defaultValuesProvider(): void
     {
         $this->markTestSkipped('Adding/dropping default constraints is not supported in MySQL.');
     }
 
-    public function testResetSequence()
+    public function testResetSequence(): void
     {
         $qb = $this->getQueryBuilder();
 
@@ -339,7 +340,7 @@ class QueryBuilderTest extends \yiiunit\framework\db\QueryBuilderTest
         return $items;
     }
 
-    public function testIssue17449()
+    public function testIssue17449(): void
     {
         $db = $this->getConnection();
         $pdo = $db->pdo;
@@ -366,7 +367,7 @@ MySqlStatement;
     /**
      * Test for issue https://github.com/yiisoft/yii2/issues/14663
      */
-    public function testInsertInteger()
+    public function testInsertInteger(): void
     {
         $db = $this->getConnection();
         $command = $db->createCommand();
@@ -391,7 +392,7 @@ MySqlStatement;
     /**
      * Test for issue https://github.com/yiisoft/yii2/issues/15500
      */
-    public function testDefaultValues()
+    public function testDefaultValues(): void
     {
         $db = $this->getConnection();
         $command = $db->createCommand();
diff --git a/tests/framework/db/mysql/QueryTest.php b/tests/framework/db/mysql/QueryTest.php
index 30d2adc1a8..6fddd84886 100644
--- a/tests/framework/db/mysql/QueryTest.php
+++ b/tests/framework/db/mysql/QueryTest.php
@@ -22,7 +22,7 @@ class QueryTest extends \yiiunit\framework\db\QueryTest
     /**
      * Tests MySQL specific syntax for index hints.
      */
-    public function testQueryIndexHint()
+    public function testQueryIndexHint(): void
     {
         $db = $this->getConnection();
 
@@ -33,7 +33,7 @@ class QueryTest extends \yiiunit\framework\db\QueryTest
         $this->assertArrayHasKey('email', $row);
     }
 
-    public function testLimitOffsetWithExpression()
+    public function testLimitOffsetWithExpression(): void
     {
         $query = (new Query())->from('customer')->select('id')->orderBy('id');
         // In MySQL limit and offset arguments must both be nonnegative integer constant
diff --git a/tests/framework/db/mysql/SchemaTest.php b/tests/framework/db/mysql/SchemaTest.php
index 91bdaa3419..b63e556c95 100644
--- a/tests/framework/db/mysql/SchemaTest.php
+++ b/tests/framework/db/mysql/SchemaTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\db\mysql;
 
+use PDO;
 use yii\db\Expression;
 use yii\db\mysql\ColumnSchema;
 use yii\db\mysql\Schema;
@@ -21,9 +22,9 @@ class SchemaTest extends \yiiunit\framework\db\SchemaTest
 {
     public $driverName = 'mysql';
 
-    public function testLoadDefaultDatetimeColumn()
+    public function testLoadDefaultDatetimeColumn(): void
     {
-        if (!version_compare($this->getConnection()->pdo->getAttribute(\PDO::ATTR_SERVER_VERSION), '5.6', '>=')) {
+        if (!version_compare($this->getConnection()->pdo->getAttribute(PDO::ATTR_SERVER_VERSION), '5.6', '>=')) {
             $this->markTestSkipped('Default datetime columns are supported since MySQL 5.6.');
         }
         $sql = <<<SQL
@@ -45,9 +46,9 @@ SQL;
         $this->assertEquals('CURRENT_TIMESTAMP', (string)$dt->defaultValue);
     }
 
-    public function testDefaultDatetimeColumnWithMicrosecs()
+    public function testDefaultDatetimeColumnWithMicrosecs(): void
     {
-        if (!version_compare($this->getConnection()->pdo->getAttribute(\PDO::ATTR_SERVER_VERSION), '5.6.4', '>=')) {
+        if (!version_compare($this->getConnection()->pdo->getAttribute(PDO::ATTR_SERVER_VERSION), '5.6.4', '>=')) {
             $this->markTestSkipped('CURRENT_TIMESTAMP with microseconds as default column value is supported since MySQL 5.6.4.');
         }
         $sql = <<<SQL
@@ -70,7 +71,7 @@ SQL;
         $this->assertEquals('CURRENT_TIMESTAMP(3)', (string)$ts->defaultValue);
     }
 
-    public function testGetSchemaNames()
+    public function testGetSchemaNames(): void
     {
         $this->markTestSkipped('Schemas are not supported in MySQL.');
     }
@@ -95,7 +96,7 @@ SQL;
      * @param string $type
      * @param mixed $expected
      */
-    public function testTableSchemaConstraints($tableName, $type, $expected)
+    public function testTableSchemaConstraints($tableName, $type, $expected): void
     {
         $version = $this->getConnection(false)->getServerVersion();
 
@@ -130,7 +131,7 @@ SQL;
      * @param string $type
      * @param mixed $expected
      */
-    public function testTableSchemaConstraintsWithPdoUppercase($tableName, $type, $expected)
+    public function testTableSchemaConstraintsWithPdoUppercase($tableName, $type, $expected): void
     {
         $version = $this->getConnection(false)->getServerVersion();
 
@@ -156,7 +157,7 @@ SQL;
         }
 
         $connection = $this->getConnection(false);
-        $connection->getSlavePdo(true)->setAttribute(\PDO::ATTR_CASE, \PDO::CASE_UPPER);
+        $connection->getSlavePdo(true)->setAttribute(PDO::ATTR_CASE, PDO::CASE_UPPER);
         $constraints = $connection->getSchema()->{'getTable' . ucfirst($type)}($tableName, true);
         $this->assertMetadataEquals($expected, $constraints);
     }
@@ -167,7 +168,7 @@ SQL;
      * @param string $type
      * @param mixed $expected
      */
-    public function testTableSchemaConstraintsWithPdoLowercase($tableName, $type, $expected)
+    public function testTableSchemaConstraintsWithPdoLowercase($tableName, $type, $expected): void
     {
         $version = $this->getConnection(false)->getServerVersion();
 
@@ -193,7 +194,7 @@ SQL;
         }
 
         $connection = $this->getConnection(false);
-        $connection->getSlavePdo(true)->setAttribute(\PDO::ATTR_CASE, \PDO::CASE_LOWER);
+        $connection->getSlavePdo(true)->setAttribute(PDO::ATTR_CASE, PDO::CASE_LOWER);
         $constraints = $connection->getSchema()->{'getTable' . ucfirst($type)}($tableName, true);
         $this->assertMetadataEquals($expected, $constraints);
     }
@@ -205,7 +206,7 @@ SQL;
      * @see https://mariadb.com/kb/en/library/now/#description
      * @see https://github.com/yiisoft/yii2/issues/15167
      */
-    public function testAlternativeDisplayOfDefaultCurrentTimestampInMariaDB()
+    public function testAlternativeDisplayOfDefaultCurrentTimestampInMariaDB(): void
     {
         /**
          * We do not have a real database MariaDB >= 10.2.3 for tests, so we emulate the information that database
@@ -235,7 +236,7 @@ SQL;
      *
      * @see https://github.com/yiisoft/yii2/issues/19047
      */
-    public function testAlternativeDisplayOfDefaultCurrentTimestampAsNullInMariaDB()
+    public function testAlternativeDisplayOfDefaultCurrentTimestampAsNullInMariaDB(): void
     {
         $schema = new Schema();
         $column = $this->invokeMethod($schema, 'loadColumnSchema', [[
diff --git a/tests/framework/db/mysql/connection/DeadLockTest.php b/tests/framework/db/mysql/connection/DeadLockTest.php
index 72559b548f..ed6bb74cec 100644
--- a/tests/framework/db/mysql/connection/DeadLockTest.php
+++ b/tests/framework/db/mysql/connection/DeadLockTest.php
@@ -8,6 +8,10 @@
 
 namespace yiiunit\framework\db\mysql\connection;
 
+use yiiunit\framework\db\mysql\ConnectionTest;
+use Throwable;
+use RuntimeException;
+use ErrorException;
 use yii\db\Connection;
 use yii\db\Exception;
 use yii\db\Transaction;
@@ -16,7 +20,7 @@ use yii\db\Transaction;
  * @group db
  * @group mysql
  */
-class DeadLockTest extends \yiiunit\framework\db\mysql\ConnectionTest
+class DeadLockTest extends ConnectionTest
 {
     /** @var string Shared log filename for children */
     private $logFile;
@@ -30,7 +34,7 @@ class DeadLockTest extends \yiiunit\framework\db\mysql\ConnectionTest
      * @link https://github.com/yiisoft/yii2/issues/12715
      * @link https://github.com/yiisoft/yii2/pull/13346
      */
-    public function testDeadlockException()
+    public function testDeadlockException(): void
     {
         if (\stripos($this->getConnection(false)->getServerVersion(), 'MariaDB') !== false) {
             $this->markTestSkipped('MariaDB does not support this test');
@@ -91,7 +95,7 @@ class DeadLockTest extends \yiiunit\framework\db\mysql\ConnectionTest
             }
             $this->deleteLog();
             throw $e;
-        } catch (\Throwable $e) {
+        } catch (Throwable $e) {
             // wait all children
             while (-1 !== pcntl_wait($status)) {
                 // nothing to do
@@ -177,7 +181,7 @@ class DeadLockTest extends \yiiunit\framework\db\mysql\ConnectionTest
                     $this->log('child 1: send signal to child 2');
                     // let child to continue
                     if (!posix_kill($pidSecond, SIGUSR1)) {
-                        throw new \RuntimeException('Cannot send signal');
+                        throw new RuntimeException('Cannot send signal');
                     }
 
                     // now child 2 tries to do the 2nd update, and hits the lock and waits
@@ -204,7 +208,7 @@ class DeadLockTest extends \yiiunit\framework\db\mysql\ConnectionTest
         } catch (\Exception $e) {
             $this->log('child 1: ! exit <<' . \get_class($e) . ' #' . $e->getCode() . ': ' . $e->getMessage() . "\n" . $e->getTraceAsString() . '>>');
             return 1;
-        } catch (\Throwable $e) {
+        } catch (Throwable $e) {
             $this->log('child 1: ! exit <<' . \get_class($e) . ' #' . $e->getCode() . ': ' . $e->getMessage() . "\n" . $e->getTraceAsString() . '>>');
             return 1;
         }
@@ -267,7 +271,7 @@ class DeadLockTest extends \yiiunit\framework\db\mysql\ConnectionTest
         } catch (\Exception $e) {
             $this->log('child 2: ! exit <<' . \get_class($e) . ' #' . $e->getCode() . ': ' . $e->getMessage() . "\n" . $e->getTraceAsString() . '>>');
             return 1;
-        } catch (\Throwable $e) {
+        } catch (Throwable $e) {
             $this->log('child 2: ! exit <<' . \get_class($e) . ' #' . $e->getCode() . ': ' . $e->getMessage() . "\n" . $e->getTraceAsString() . '>>');
             return 1;
         }
@@ -281,11 +285,11 @@ class DeadLockTest extends \yiiunit\framework\db\mysql\ConnectionTest
      * all the rest tests. So, all the rest tests in this case will run both in the child
      * and parent processes. Such mess must be prevented with child's own error handler.
      */
-    private function setErrorHandler()
+    private function setErrorHandler(): void
     {
         if (PHP_VERSION_ID < 70000) {
             set_error_handler(function ($errno, $errstr, $errfile, $errline) {
-                throw new \ErrorException($errstr, $errno, $errno, $errfile, $errline);
+                throw new ErrorException($errstr, $errno, $errno, $errfile, $errline);
             });
         }
     }
@@ -294,7 +298,7 @@ class DeadLockTest extends \yiiunit\framework\db\mysql\ConnectionTest
      * Sets filename for log file shared between children processes.
      * @param string $filename
      */
-    private function setLogFile($filename)
+    private function setLogFile($filename): void
     {
         $this->logFile = $filename;
     }
@@ -303,7 +307,7 @@ class DeadLockTest extends \yiiunit\framework\db\mysql\ConnectionTest
      * Deletes shared log file.
      * Deletes the file [[logFile]] if it exists.
      */
-    private function deleteLog()
+    private function deleteLog(): void
     {
         if (null !== $this->logFile && is_file($this->logFile)) {
             unlink($this->logFile);
@@ -333,7 +337,7 @@ class DeadLockTest extends \yiiunit\framework\db\mysql\ConnectionTest
      * @param string $message Message to append to the log. The message will be prepended
      * with timestamp and appended with new line.
      */
-    private function log($message)
+    private function log($message): void
     {
         if (null !== $this->logFile) {
             $time = microtime(true);
diff --git a/tests/framework/db/oci/ActiveRecordTest.php b/tests/framework/db/oci/ActiveRecordTest.php
index 63a57b62f6..98be9d4b11 100644
--- a/tests/framework/db/oci/ActiveRecordTest.php
+++ b/tests/framework/db/oci/ActiveRecordTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\db\oci;
 
+use yii\db\ActiveRecordInterface;
 use yii\db\ActiveQuery;
 use yiiunit\data\ar\BitValues;
 use yiiunit\data\ar\DefaultPk;
@@ -23,7 +24,7 @@ class ActiveRecordTest extends \yiiunit\framework\db\ActiveRecordTest
 {
     protected $driverName = 'oci';
 
-    public function testCastValues()
+    public function testCastValues(): void
     {
         // pass, because boolean casting is not available
         $model = new Type();
@@ -53,7 +54,7 @@ class ActiveRecordTest extends \yiiunit\framework\db\ActiveRecordTest
         $this->assertEquals('0', $model->bool_col2);
     }
 
-    public function testDefaultValues()
+    public function testDefaultValues(): void
     {
         $model = new Type();
         $model->loadDefaultValues();
@@ -78,9 +79,9 @@ class ActiveRecordTest extends \yiiunit\framework\db\ActiveRecordTest
         $this->assertEquals('something', $model->char_col2);
     }
 
-    public function testFindAsArray()
+    public function testFindAsArray(): void
     {
-        /** @var \yii\db\ActiveRecordInterface $customerClass */
+        /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
 
         // asArray
@@ -118,7 +119,7 @@ class ActiveRecordTest extends \yiiunit\framework\db\ActiveRecordTest
         $this->assertArrayHasKey('bool_status', $customers[2]);
     }
 
-    public function testPrimaryKeyAfterSave()
+    public function testPrimaryKeyAfterSave(): void
     {
         $record = new DefaultPk();
         $record->type = 'type';
@@ -126,7 +127,7 @@ class ActiveRecordTest extends \yiiunit\framework\db\ActiveRecordTest
         $this->assertEquals(5, $record->primaryKey);
     }
 
-    public function testMultiplePrimaryKeyAfterSave()
+    public function testMultiplePrimaryKeyAfterSave(): void
     {
         $record = new DefaultMultiplePk();
         $record->id = 5;
@@ -140,7 +141,7 @@ class ActiveRecordTest extends \yiiunit\framework\db\ActiveRecordTest
     /**
      * @see https://github.com/yiisoft/yii2/issues/9006
      */
-    public function testBit()
+    public function testBit(): void
     {
         $falseBit = BitValues::findOne(1);
         $this->assertEquals('0', $falseBit->val);
@@ -153,11 +154,10 @@ class ActiveRecordTest extends \yiiunit\framework\db\ActiveRecordTest
      * Some PDO implementations(e.g. cubrid) do not support boolean values.
      * Make sure this does not affect AR layer.
      */
-    public function testBooleanAttribute()
+    public function testBooleanAttribute(): void
     {
         /** @var TestCase|ActiveRecordTestTrait $this */
-
-        /** @var \yii\db\ActiveRecordInterface $customerClass */
+        /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
         $customer = new $customerClass();
         $customer->name = 'boolean customer';
@@ -186,7 +186,7 @@ class ActiveRecordTest extends \yiiunit\framework\db\ActiveRecordTest
      * @dataProvider aliasMethodProvider
      * @param string $aliasMethod whether alias is specified explicitly or using the query syntax {{@tablename}}
      */
-    public function testJoinWithAlias($aliasMethod)
+    public function testJoinWithAlias($aliasMethod): void
     {
         // left join and eager loading
         /** @var ActiveQuery $query */
diff --git a/tests/framework/db/oci/CommandTest.php b/tests/framework/db/oci/CommandTest.php
index 0c49c922ae..470ac8924b 100644
--- a/tests/framework/db/oci/CommandTest.php
+++ b/tests/framework/db/oci/CommandTest.php
@@ -8,6 +8,8 @@
 
 namespace yiiunit\framework\db\oci;
 
+use Exception;
+use Throwable;
 use yii\caching\ArrayCache;
 use yii\db\Connection;
 use yii\db\Query;
@@ -21,7 +23,7 @@ class CommandTest extends \yiiunit\framework\db\CommandTest
 {
     protected $driverName = 'oci';
 
-    public function testAutoQuoting()
+    public function testAutoQuoting(): void
     {
         $db = $this->getConnection(false);
 
@@ -30,7 +32,7 @@ class CommandTest extends \yiiunit\framework\db\CommandTest
         $this->assertEquals('SELECT "id", "t"."name" FROM "customer" t', $command->sql);
     }
 
-    public function testLastInsertId()
+    public function testLastInsertId(): void
     {
         $db = $this->getConnection();
 
@@ -58,7 +60,7 @@ class CommandTest extends \yiiunit\framework\db\CommandTest
      *
      * @return void
      */
-    public function testCLOBStringInsertion()
+    public function testCLOBStringInsertion(): void
     {
         $db = $this->getConnection();
 
@@ -78,7 +80,7 @@ class CommandTest extends \yiiunit\framework\db\CommandTest
         $db->createCommand()->dropTable('longstring')->execute();
     }
 
-    public function testQueryCache()
+    public function testQueryCache(): void
     {
         $db = $this->getConnection(true);
 
@@ -168,7 +170,7 @@ class CommandTest extends \yiiunit\framework\db\CommandTest
         ];
     }
 
-    public function testInsert()
+    public function testInsert(): void
     {
         $db = $this->getConnection();
         $db->createCommand('DELETE FROM {{customer}}')->execute();
@@ -194,7 +196,7 @@ class CommandTest extends \yiiunit\framework\db\CommandTest
     /**
      * Test INSERT INTO ... SELECT SQL statement with alias syntax.
      */
-    public function testInsertSelectAlias()
+    public function testInsertSelectAlias(): void
     {
         $db = $this->getConnection();
 
@@ -245,7 +247,7 @@ class CommandTest extends \yiiunit\framework\db\CommandTest
      *
      * https://github.com/yiisoft/yii2/issues/6526
      */
-    public function testBatchInsertDataTypesLocale()
+    public function testBatchInsertDataTypesLocale(): void
     {
         $locale = setlocale(LC_NUMERIC, 0);
         if (false === $locale) {
@@ -290,10 +292,10 @@ class CommandTest extends \yiiunit\framework\db\CommandTest
             $this->assertEquals('1', $data[0]['bool_col']);
             $this->assertIsOneOf($data[1]['bool_col'], ['0', false]);
             $this->assertIsOneOf($data[2]['bool_col'], ['0', false]);
-        } catch (\Exception $e) {
+        } catch (Exception $e) {
             setlocale(LC_NUMERIC, $locale);
             throw $e;
-        } catch (\Throwable $e) {
+        } catch (Throwable $e) {
             setlocale(LC_NUMERIC, $locale);
             throw $e;
         }
@@ -303,7 +305,7 @@ class CommandTest extends \yiiunit\framework\db\CommandTest
     /**
      * verify that {{}} are not going to be replaced in parameters.
      */
-    public function testNoTablenameReplacement()
+    public function testNoTablenameReplacement(): void
     {
         $db = $this->getConnection();
 
@@ -335,7 +337,7 @@ class CommandTest extends \yiiunit\framework\db\CommandTest
         $this->assertEquals('Some {{%updated}} address', $customer['address']);
     }
 
-    public function testCreateTable()
+    public function testCreateTable(): void
     {
         $db = $this->getConnection();
 
@@ -362,7 +364,7 @@ class CommandTest extends \yiiunit\framework\db\CommandTest
         ], $records);
     }
 
-    public function testsInsertQueryAsColumnValue()
+    public function testsInsertQueryAsColumnValue(): void
     {
         $time = time();
 
@@ -378,7 +380,7 @@ class CommandTest extends \yiiunit\framework\db\CommandTest
 
         $orderId = $db->getLastInsertID('order_SEQ');
 
-        $columnValueQuery = new \yii\db\Query();
+        $columnValueQuery = new Query();
         $columnValueQuery->select('created_at')->from('{{order}}')->where(['id' => $orderId]);
 
         $command = $db->createCommand();
@@ -399,7 +401,7 @@ class CommandTest extends \yiiunit\framework\db\CommandTest
         $db->createCommand('DELETE FROM {{order}} WHERE [[id]] = ' . $orderId)->execute();
     }
 
-    public function testAlterTable()
+    public function testAlterTable(): void
     {
         $db = $this->getConnection();
 
@@ -439,7 +441,7 @@ class CommandTest extends \yiiunit\framework\db\CommandTest
         ], $records);
     }
 
-    public function testCreateView()
+    public function testCreateView(): void
     {
         $db = $this->getConnection();
 
@@ -479,7 +481,7 @@ class CommandTest extends \yiiunit\framework\db\CommandTest
         $this->assertEquals([['bar' => 6]], $records);
     }
 
-    public function testColumnCase()
+    public function testColumnCase(): void
     {
         $this->markTestSkipped('Should be fixed.');
     }
diff --git a/tests/framework/db/oci/ConnectionTest.php b/tests/framework/db/oci/ConnectionTest.php
index 2edf3b0432..a8cf7185ba 100644
--- a/tests/framework/db/oci/ConnectionTest.php
+++ b/tests/framework/db/oci/ConnectionTest.php
@@ -19,7 +19,7 @@ class ConnectionTest extends \yiiunit\framework\db\ConnectionTest
 {
     protected $driverName = 'oci';
 
-    public function testSerialize()
+    public function testSerialize(): void
     {
         $connection = $this->getConnection(false, false);
         $connection->open();
@@ -30,7 +30,7 @@ class ConnectionTest extends \yiiunit\framework\db\ConnectionTest
         $this->assertEquals(123, $unserialized->createCommand('SELECT 123 FROM DUAL')->queryScalar());
     }
 
-    public function testQuoteTableName()
+    public function testQuoteTableName(): void
     {
         $connection = $this->getConnection(false);
         $this->assertEquals('"table"', $connection->quoteTableName('table'));
@@ -42,7 +42,7 @@ class ConnectionTest extends \yiiunit\framework\db\ConnectionTest
         $this->assertEquals('(table)', $connection->quoteTableName('(table)'));
     }
 
-    public function testQuoteColumnName()
+    public function testQuoteColumnName(): void
     {
         $connection = $this->getConnection(false);
         $this->assertEquals('"column"', $connection->quoteColumnName('column'));
@@ -55,7 +55,7 @@ class ConnectionTest extends \yiiunit\framework\db\ConnectionTest
         $this->assertEquals('"column"', $connection->quoteSql('{{column}}'));
     }
 
-    public function testQuoteFullColumnName()
+    public function testQuoteFullColumnName(): void
     {
         $connection = $this->getConnection(false, false);
         $this->assertEquals('"table"."column"', $connection->quoteColumnName('table.column'));
@@ -77,7 +77,7 @@ class ConnectionTest extends \yiiunit\framework\db\ConnectionTest
         $this->assertEquals('"table"."column"', $connection->quoteSql('{{%table}}."column"'));
     }
 
-    public function testTransactionIsolation()
+    public function testTransactionIsolation(): void
     {
         $connection = $this->getConnection(true);
 
@@ -96,7 +96,7 @@ class ConnectionTest extends \yiiunit\framework\db\ConnectionTest
      *
      * Change Transaction::READ_UNCOMMITTED => Transaction::READ_COMMITTED.
      */
-    public function testTransactionShortcutCustom()
+    public function testTransactionShortcutCustom(): void
     {
         $connection = $this->getConnection(true);
 
@@ -113,7 +113,7 @@ class ConnectionTest extends \yiiunit\framework\db\ConnectionTest
         $this->assertEquals(1, $profilesCount, 'profile should be inserted in transaction shortcut');
     }
 
-    public function testQuoteValue()
+    public function testQuoteValue(): void
     {
         $connection = $this->getConnection(false);
         $this->assertEquals(123, $connection->quoteValue(123));
diff --git a/tests/framework/db/oci/QueryBuilderTest.php b/tests/framework/db/oci/QueryBuilderTest.php
index 2e6503a511..92e4047059 100644
--- a/tests/framework/db/oci/QueryBuilderTest.php
+++ b/tests/framework/db/oci/QueryBuilderTest.php
@@ -8,6 +8,9 @@
 
 namespace yiiunit\framework\db\oci;
 
+use Closure;
+use Exception;
+use yii\base\NotSupportedException;
 use yii\db\oci\QueryBuilder;
 use yii\db\oci\Schema;
 use yii\helpers\ArrayHelper;
@@ -81,12 +84,12 @@ class QueryBuilderTest extends \yiiunit\framework\db\QueryBuilderTest
      * @dataProvider defaultValuesProvider
      * @param string $sql
      */
-    public function testAddDropDefaultValue($sql, \Closure $builder)
+    public function testAddDropDefaultValue($sql, Closure $builder): void
     {
         $this->markTestSkipped('Adding/dropping default constraints is not supported in Oracle.');
     }
 
-    public function testCommentColumn()
+    public function testCommentColumn(): void
     {
         $qb = $this->getQueryBuilder();
 
@@ -99,7 +102,7 @@ class QueryBuilderTest extends \yiiunit\framework\db\QueryBuilderTest
         $this->assertEquals($this->replaceQuotes($expected), $sql);
     }
 
-    public function testCommentTable()
+    public function testCommentTable(): void
     {
         $qb = $this->getQueryBuilder();
 
@@ -112,7 +115,7 @@ class QueryBuilderTest extends \yiiunit\framework\db\QueryBuilderTest
         $this->assertEquals($this->replaceQuotes($expected), $sql);
     }
 
-    public function testExecuteResetSequence()
+    public function testExecuteResetSequence(): void
     {
         $db = $this->getConnection();
         $qb = $this->getQueryBuilder();
@@ -136,7 +139,7 @@ class QueryBuilderTest extends \yiiunit\framework\db\QueryBuilderTest
         try {
             $encodedBackslash = substr($this->getDb()->quoteValue('\\'), 1, -1);
             $this->likeParameterReplacements[$encodedBackslash] = '\\';
-        } catch (\Exception $e) {
+        } catch (Exception $e) {
             $this->markTestSkipped('Could not execute Connection::quoteValue() method: ' . $e->getMessage());
         }
 
@@ -283,7 +286,7 @@ WHERE rownum <= 1) "EXCLUDED" ON ("T_upsert"."email"="EXCLUDED"."email") WHEN NO
     /**
      * Dummy test to speed up QB's tests which rely on DB schema
      */
-    public function testInitFixtures()
+    public function testInitFixtures(): void
     {
         $this->assertInstanceOf('yii\db\QueryBuilder', $this->getQueryBuilder(true, true));
     }
@@ -296,10 +299,10 @@ WHERE rownum <= 1) "EXCLUDED" ON ("T_upsert"."email"="EXCLUDED"."email") WHEN NO
      * @param array|null $updateColumns
      * @param string|string[] $expectedSQL
      * @param array $expectedParams
-     * @throws \yii\base\NotSupportedException
-     * @throws \Exception
+     * @throws NotSupportedException
+     * @throws Exception
      */
-    public function testUpsert($table, $insertColumns, $updateColumns, $expectedSQL, $expectedParams)
+    public function testUpsert($table, $insertColumns, $updateColumns, $expectedSQL, $expectedParams): void
     {
         $actualParams = [];
         $actualSQL = $this->getQueryBuilder(true, $this->driverName === 'sqlite')->upsert($table, $insertColumns, $updateColumns, $actualParams);
diff --git a/tests/framework/db/oci/QueryTest.php b/tests/framework/db/oci/QueryTest.php
index 292a7a1921..e88ccaf3e8 100644
--- a/tests/framework/db/oci/QueryTest.php
+++ b/tests/framework/db/oci/QueryTest.php
@@ -16,7 +16,7 @@ class QueryTest extends \yiiunit\framework\db\QueryTest
 {
     protected $driverName = 'oci';
 
-    public function testUnion()
+    public function testUnion(): void
     {
         $this->markTestSkipped('Unsupported use of WITH clause in Oracle.');
     }
diff --git a/tests/framework/db/oci/SchemaTest.php b/tests/framework/db/oci/SchemaTest.php
index 99e224b6c9..cea1d2e478 100644
--- a/tests/framework/db/oci/SchemaTest.php
+++ b/tests/framework/db/oci/SchemaTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\db\oci;
 
+use Exception;
 use yii\db\CheckConstraint;
 use yiiunit\framework\db\AnyValue;
 
@@ -103,7 +104,7 @@ class SchemaTest extends \yiiunit\framework\db\SchemaTest
      * Autoincrement columns detection should be disabled for Oracle
      * because there is no way of associating a column with a sequence.
      */
-    public function testAutoincrementDisabled()
+    public function testAutoincrementDisabled(): void
     {
         $table = $this->getConnection(false)->schema->getTableSchema('order', true);
         $this->assertFalse($table->columns['id']->autoIncrement);
@@ -177,7 +178,7 @@ class SchemaTest extends \yiiunit\framework\db\SchemaTest
         return $result;
     }
 
-    public function testFindUniqueIndexes()
+    public function testFindUniqueIndexes(): void
     {
         if ($this->driverName === 'sqlsrv') {
             $this->markTestSkipped('`\yii\db\mssql\Schema::findUniqueIndexes()` returns only unique constraints not unique indexes.');
@@ -187,7 +188,7 @@ class SchemaTest extends \yiiunit\framework\db\SchemaTest
 
         try {
             $db->createCommand()->dropTable('uniqueIndex')->execute();
-        } catch (\Exception $e) {
+        } catch (Exception $e) {
         }
         $db->createCommand()->createTable('uniqueIndex', [
             'somecol' => 'string',
@@ -229,7 +230,7 @@ class SchemaTest extends \yiiunit\framework\db\SchemaTest
         ], $uniqueIndexes);
     }
 
-    public function testCompositeFk()
+    public function testCompositeFk(): void
     {
         $this->markTestSkipped('Should be fixed.');
     }
diff --git a/tests/framework/db/oci/UniqueValidatorTest.php b/tests/framework/db/oci/UniqueValidatorTest.php
index 2ed63a7595..300002ff2d 100644
--- a/tests/framework/db/oci/UniqueValidatorTest.php
+++ b/tests/framework/db/oci/UniqueValidatorTest.php
@@ -20,7 +20,7 @@ class UniqueValidatorTest extends \yiiunit\framework\validators\UniqueValidatorT
 {
     public $driverName = 'oci';
 
-    public function testValidateEmptyAttributeInStringField()
+    public function testValidateEmptyAttributeInStringField(): void
     {
         ValidatorTestMainModel::deleteAll();
 
diff --git a/tests/framework/db/pgsql/ActiveFixtureTest.php b/tests/framework/db/pgsql/ActiveFixtureTest.php
index c00886c728..281874d55e 100644
--- a/tests/framework/db/pgsql/ActiveFixtureTest.php
+++ b/tests/framework/db/pgsql/ActiveFixtureTest.php
@@ -19,7 +19,7 @@ class ActiveFixtureTest extends \yiiunit\framework\test\ActiveFixtureTest
 {
     public $driverName = 'pgsql';
 
-    public function testFixturesLoadingResetsSeqence()
+    public function testFixturesLoadingResetsSeqence(): void
     {
         $test = new CustomerDbTestCase();
         $test->setUp();
diff --git a/tests/framework/db/pgsql/ActiveRecordTest.php b/tests/framework/db/pgsql/ActiveRecordTest.php
index 67c8041128..1f6f32c407 100644
--- a/tests/framework/db/pgsql/ActiveRecordTest.php
+++ b/tests/framework/db/pgsql/ActiveRecordTest.php
@@ -27,7 +27,7 @@ class ActiveRecordTest extends \yiiunit\framework\db\ActiveRecordTest
 {
     protected $driverName = 'pgsql';
 
-    public function testBooleanAttribute()
+    public function testBooleanAttribute(): void
     {
         /** @var TestCase|ActiveRecordTestTrait $this */
 
@@ -55,7 +55,7 @@ class ActiveRecordTest extends \yiiunit\framework\db\ActiveRecordTest
         $this->assertCount(1, $customers);
     }
 
-    public function testFindAsArray()
+    public function testFindAsArray(): void
     {
         /** @var ActiveRecordInterface $customerClass */
         $customerClass = $this->getCustomerClass();
@@ -95,7 +95,7 @@ class ActiveRecordTest extends \yiiunit\framework\db\ActiveRecordTest
         $this->assertArrayHasKey('bool_status', $customers[2]);
     }
 
-    public function testBooleanValues()
+    public function testBooleanValues(): void
     {
         $db = $this->getConnection();
         $command = $db->createCommand();
@@ -126,7 +126,7 @@ class ActiveRecordTest extends \yiiunit\framework\db\ActiveRecordTest
     /**
      * @see https://github.com/yiisoft/yii2/issues/4672
      */
-    public function testBooleanValues2()
+    public function testBooleanValues2(): void
     {
         $db = $this->getConnection();
         $db->charset = 'utf8';
@@ -159,7 +159,7 @@ class ActiveRecordTest extends \yiiunit\framework\db\ActiveRecordTest
         $this->assertCount(1, UserAR::find()->where(['is_deleted' => [true, false]])->all($db));
     }
 
-    public function testBooleanDefaultValues()
+    public function testBooleanDefaultValues(): void
     {
         $model = new BoolAR();
         $this->assertNull($model->bool_col);
@@ -173,7 +173,7 @@ class ActiveRecordTest extends \yiiunit\framework\db\ActiveRecordTest
         $this->assertTrue($model->save(false));
     }
 
-    public function testPrimaryKeyAfterSave()
+    public function testPrimaryKeyAfterSave(): void
     {
         $record = new DefaultPk();
         $record->type = 'type';
@@ -184,7 +184,7 @@ class ActiveRecordTest extends \yiiunit\framework\db\ActiveRecordTest
     /**
      * @dataProvider arrayValuesProvider $attributes
      */
-    public function testArrayValues($attributes)
+    public function testArrayValues($attributes): void
     {
         $type = new ArrayAndJsonTypes();
         foreach ($attributes as $attribute => $expected) {
diff --git a/tests/framework/db/pgsql/ArrayParserTest.php b/tests/framework/db/pgsql/ArrayParserTest.php
index a58237ab4b..6aa8d6ba3d 100644
--- a/tests/framework/db/pgsql/ArrayParserTest.php
+++ b/tests/framework/db/pgsql/ArrayParserTest.php
@@ -39,7 +39,7 @@ class ArrayParserTest extends TestCase
     /**
      * @dataProvider convertProvider
      */
-    public function testConvert($string, $expected)
+    public function testConvert($string, $expected): void
     {
         $this->assertSame($expected, $this->arrayParser->parse($string));
     }
diff --git a/tests/framework/db/pgsql/BaseActiveRecordTest.php b/tests/framework/db/pgsql/BaseActiveRecordTest.php
index db6f126481..c0af29e83f 100644
--- a/tests/framework/db/pgsql/BaseActiveRecordTest.php
+++ b/tests/framework/db/pgsql/BaseActiveRecordTest.php
@@ -18,7 +18,7 @@ class BaseActiveRecordTest extends \yiiunit\framework\db\BaseActiveRecordTest
      *
      * @dataProvider provideArrayValueWithChange
      */
-    public function testJsonDirtyAttributesWithDataChange($actual, $modified)
+    public function testJsonDirtyAttributesWithDataChange($actual, $modified): void
     {
         $createdStorage = new ArrayAndJsonType([
             'json_col' => new JsonExpression($actual),
diff --git a/tests/framework/db/pgsql/CommandTest.php b/tests/framework/db/pgsql/CommandTest.php
index 6357e9c2d8..23fe9f8026 100644
--- a/tests/framework/db/pgsql/CommandTest.php
+++ b/tests/framework/db/pgsql/CommandTest.php
@@ -19,7 +19,7 @@ class CommandTest extends \yiiunit\framework\db\CommandTest
 {
     public $driverName = 'pgsql';
 
-    public function testAutoQuoting()
+    public function testAutoQuoting(): void
     {
         $db = $this->getConnection(false);
 
@@ -28,7 +28,7 @@ class CommandTest extends \yiiunit\framework\db\CommandTest
         $this->assertEquals('SELECT "id", "t"."name" FROM "customer" t', $command->sql);
     }
 
-    public function testBooleanValuesInsert()
+    public function testBooleanValuesInsert(): void
     {
         $db = $this->getConnection();
         $command = $db->createCommand();
@@ -45,7 +45,7 @@ class CommandTest extends \yiiunit\framework\db\CommandTest
         $this->assertEquals(1, $command->queryScalar());
     }
 
-    public function testBooleanValuesBatchInsert()
+    public function testBooleanValuesBatchInsert(): void
     {
         $db = $this->getConnection();
         $command = $db->createCommand();
@@ -65,7 +65,7 @@ class CommandTest extends \yiiunit\framework\db\CommandTest
         $this->assertEquals(1, $command->queryScalar());
     }
 
-    public function testLastInsertId()
+    public function testLastInsertId(): void
     {
         $db = $this->getConnection();
 
@@ -94,7 +94,7 @@ class CommandTest extends \yiiunit\framework\db\CommandTest
     /**
      * @see https://github.com/yiisoft/yii2/issues/11498
      */
-    public function testSaveSerializedObject()
+    public function testSaveSerializedObject(): void
     {
         if (\defined('HHVM_VERSION')) {
             $this->markTestSkipped('HHVMs PgSQL implementation does not seem to support blob colums in the way they are used here.');
@@ -157,7 +157,7 @@ class CommandTest extends \yiiunit\framework\db\CommandTest
     /**
      * @see https://github.com/yiisoft/yii2/issues/15827
      */
-    public function testIssue15827()
+    public function testIssue15827(): void
     {
         $db = $this->getConnection();
 
diff --git a/tests/framework/db/pgsql/ConnectionTest.php b/tests/framework/db/pgsql/ConnectionTest.php
index a7fb939a36..73f141bbcc 100644
--- a/tests/framework/db/pgsql/ConnectionTest.php
+++ b/tests/framework/db/pgsql/ConnectionTest.php
@@ -18,12 +18,12 @@ class ConnectionTest extends \yiiunit\framework\db\ConnectionTest
 {
     protected $driverName = 'pgsql';
 
-    public function testConnection()
+    public function testConnection(): void
     {
         $this->assertIsObject($this->getConnection(true));
     }
 
-    public function testQuoteValue()
+    public function testQuoteValue(): void
     {
         $connection = $this->getConnection(false);
         $this->assertEquals(123, $connection->quoteValue(123));
@@ -31,7 +31,7 @@ class ConnectionTest extends \yiiunit\framework\db\ConnectionTest
         $this->assertEquals("'It''s interesting'", $connection->quoteValue("It's interesting"));
     }
 
-    public function testQuoteTableName()
+    public function testQuoteTableName(): void
     {
         $connection = $this->getConnection(false);
         $this->assertEquals('"table"', $connection->quoteTableName('table'));
@@ -43,7 +43,7 @@ class ConnectionTest extends \yiiunit\framework\db\ConnectionTest
         $this->assertEquals('(table)', $connection->quoteTableName('(table)'));
     }
 
-    public function testQuoteColumnName()
+    public function testQuoteColumnName(): void
     {
         $connection = $this->getConnection(false);
         $this->assertEquals('"column"', $connection->quoteColumnName('column'));
@@ -56,7 +56,7 @@ class ConnectionTest extends \yiiunit\framework\db\ConnectionTest
         $this->assertEquals('"column"', $connection->quoteSql('{{column}}'));
     }
 
-    public function testQuoteFullColumnName()
+    public function testQuoteFullColumnName(): void
     {
         $connection = $this->getConnection(false, false);
         $this->assertEquals('"table"."column"', $connection->quoteColumnName('table.column'));
@@ -78,7 +78,7 @@ class ConnectionTest extends \yiiunit\framework\db\ConnectionTest
         $this->assertEquals('"table"."column"', $connection->quoteSql('{{%table}}."column"'));
     }
 
-    public function testTransactionIsolation()
+    public function testTransactionIsolation(): void
     {
         $connection = $this->getConnection(true);
 
diff --git a/tests/framework/db/pgsql/ExistValidatorTest.php b/tests/framework/db/pgsql/ExistValidatorTest.php
index bb937830ae..968ec61933 100644
--- a/tests/framework/db/pgsql/ExistValidatorTest.php
+++ b/tests/framework/db/pgsql/ExistValidatorTest.php
@@ -22,7 +22,7 @@ class ExistValidatorTest extends \yiiunit\framework\validators\ExistValidatorTes
     /**
      * @see https://github.com/yiisoft/yii2/issues/14274
      */
-    public function testWithCameCasedTableName()
+    public function testWithCameCasedTableName(): void
     {
         // The same target table
         $validator = new ExistValidator(['targetAttribute' => 'ref']);
diff --git a/tests/framework/db/pgsql/QueryBuilderTest.php b/tests/framework/db/pgsql/QueryBuilderTest.php
index ee108070a0..501e7fe211 100644
--- a/tests/framework/db/pgsql/QueryBuilderTest.php
+++ b/tests/framework/db/pgsql/QueryBuilderTest.php
@@ -155,7 +155,7 @@ class QueryBuilderTest extends \yiiunit\framework\db\QueryBuilderTest
         ]);
     }
 
-    public function testAlterColumn()
+    public function testAlterColumn(): void
     {
         $qb = $this->getQueryBuilder();
 
@@ -211,12 +211,12 @@ class QueryBuilderTest extends \yiiunit\framework\db\QueryBuilderTest
         return $result;
     }
 
-    public function defaultValuesProvider()
+    public function defaultValuesProvider(): void
     {
         $this->markTestSkipped('Adding/dropping default constraints is not supported in PostgreSQL.');
     }
 
-    public function testCommentColumn()
+    public function testCommentColumn(): void
     {
         $qb = $this->getQueryBuilder();
 
@@ -229,7 +229,7 @@ class QueryBuilderTest extends \yiiunit\framework\db\QueryBuilderTest
         $this->assertEquals($this->replaceQuotes($expected), $sql);
     }
 
-    public function testCommentTable()
+    public function testCommentTable(): void
     {
         $qb = $this->getQueryBuilder();
 
@@ -253,7 +253,7 @@ class QueryBuilderTest extends \yiiunit\framework\db\QueryBuilderTest
         return $data;
     }
 
-    public function testResetSequence()
+    public function testResetSequence(): void
     {
         $qb = $this->getQueryBuilder();
 
@@ -266,7 +266,7 @@ class QueryBuilderTest extends \yiiunit\framework\db\QueryBuilderTest
         $this->assertEquals($expected, $sql);
     }
 
-    public function testResetSequencePostgres12()
+    public function testResetSequencePostgres12(): void
     {
         if (version_compare($this->getConnection(false)->getServerVersion(), '12.0', '<')) {
             $this->markTestSkipped('PostgreSQL < 12.0 does not support GENERATED AS IDENTITY columns.');
@@ -409,7 +409,7 @@ class QueryBuilderTest extends \yiiunit\framework\db\QueryBuilderTest
         return $items;
     }
 
-    public function testDropIndex()
+    public function testDropIndex(): void
     {
         $qb = $this->getQueryBuilder();
 
diff --git a/tests/framework/db/pgsql/QueryTest.php b/tests/framework/db/pgsql/QueryTest.php
index df8d370840..830010136e 100644
--- a/tests/framework/db/pgsql/QueryTest.php
+++ b/tests/framework/db/pgsql/QueryTest.php
@@ -18,7 +18,7 @@ class QueryTest extends \yiiunit\framework\db\QueryTest
 {
     public $driverName = 'pgsql';
 
-    public function testBooleanValues()
+    public function testBooleanValues(): void
     {
         $db = $this->getConnection();
         $command = $db->createCommand();
diff --git a/tests/framework/db/pgsql/SchemaTest.php b/tests/framework/db/pgsql/SchemaTest.php
index 66e7c5e84e..1fe2655cd2 100644
--- a/tests/framework/db/pgsql/SchemaTest.php
+++ b/tests/framework/db/pgsql/SchemaTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\db\pgsql;
 
+use PDO;
 use yii\db\Expression;
 use yiiunit\data\ar\ActiveRecord;
 use yiiunit\data\ar\EnumTypeInCustomSchema;
@@ -163,7 +164,7 @@ class SchemaTest extends \yiiunit\framework\db\SchemaTest
         return $columns;
     }
 
-    public function testCompositeFk()
+    public function testCompositeFk(): void
     {
         $schema = $this->getConnection()->schema;
 
@@ -176,18 +177,18 @@ class SchemaTest extends \yiiunit\framework\db\SchemaTest
         $this->assertEquals('item_id', $table->foreignKeys['fk_composite_fk_order_item']['item_id']);
     }
 
-    public function testGetPDOType()
+    public function testGetPDOType(): void
     {
         $values = [
-            [null, \PDO::PARAM_NULL],
-            ['', \PDO::PARAM_STR],
-            ['hello', \PDO::PARAM_STR],
-            [0, \PDO::PARAM_INT],
-            [1, \PDO::PARAM_INT],
-            [1337, \PDO::PARAM_INT],
-            [true, \PDO::PARAM_BOOL],
-            [false, \PDO::PARAM_BOOL],
-            [$fp = fopen(__FILE__, 'rb'), \PDO::PARAM_LOB],
+            [null, PDO::PARAM_NULL],
+            ['', PDO::PARAM_STR],
+            ['hello', PDO::PARAM_STR],
+            [0, PDO::PARAM_INT],
+            [1, PDO::PARAM_INT],
+            [1337, PDO::PARAM_INT],
+            [true, PDO::PARAM_BOOL],
+            [false, PDO::PARAM_BOOL],
+            [$fp = fopen(__FILE__, 'rb'), PDO::PARAM_LOB],
         ];
 
         $schema = $this->getConnection()->schema;
@@ -198,7 +199,7 @@ class SchemaTest extends \yiiunit\framework\db\SchemaTest
         fclose($fp);
     }
 
-    public function testBooleanDefaultValues()
+    public function testBooleanDefaultValues(): void
     {
         $schema = $this->getConnection()->schema;
 
@@ -207,7 +208,7 @@ class SchemaTest extends \yiiunit\framework\db\SchemaTest
         $this->assertFalse($table->getColumn('default_false')->defaultValue);
     }
 
-    public function testSequenceName()
+    public function testSequenceName(): void
     {
         $connection = $this->getConnection();
 
@@ -223,7 +224,7 @@ class SchemaTest extends \yiiunit\framework\db\SchemaTest
         $this->assertEquals($sequenceName, $connection->schema->getTableSchema('item')->sequenceName);
     }
 
-    public function testGeneratedValues()
+    public function testGeneratedValues(): void
     {
         if (version_compare($this->getConnection(false)->getServerVersion(), '12.0', '<')) {
             $this->markTestSkipped('PostgreSQL < 12.0 does not support GENERATED AS IDENTITY columns.');
@@ -240,7 +241,7 @@ class SchemaTest extends \yiiunit\framework\db\SchemaTest
         $this->assertTrue($table->getColumn('id_default')->autoIncrement);
     }
 
-    public function testPartitionedTable()
+    public function testPartitionedTable(): void
     {
         if (version_compare($this->getConnection(false)->getServerVersion(), '10.0', '<')) {
             $this->markTestSkipped('PostgreSQL < 10.0 does not support PARTITION BY clause.');
@@ -253,7 +254,7 @@ class SchemaTest extends \yiiunit\framework\db\SchemaTest
         $this->assertNotNull($this->getConnection(false)->schema->getTableSchema('partitioned'));
     }
 
-    public function testFindSchemaNames()
+    public function testFindSchemaNames(): void
     {
         $schema = $this->getConnection()->schema;
 
@@ -277,7 +278,7 @@ class SchemaTest extends \yiiunit\framework\db\SchemaTest
      * @dataProvider bigintValueProvider
      * @param int $bigint
      */
-    public function testBigintValue($bigint)
+    public function testBigintValue($bigint): void
     {
         $this->mockApplication();
         ActiveRecord::$db = $this->getConnection();
@@ -299,7 +300,7 @@ class SchemaTest extends \yiiunit\framework\db\SchemaTest
     /**
      * @see https://github.com/yiisoft/yii2/issues/12483
      */
-    public function testParenthesisDefaultValue()
+    public function testParenthesisDefaultValue(): void
     {
         $db = $this->getConnection(false);
         if ($db->schema->getTableSchema('test_default_parenthesis') !== null) {
@@ -324,7 +325,7 @@ class SchemaTest extends \yiiunit\framework\db\SchemaTest
     /**
      * @see https://github.com/yiisoft/yii2/issues/14192
      */
-    public function testTimestampNullDefaultValue()
+    public function testTimestampNullDefaultValue(): void
     {
         $db = $this->getConnection(false);
         if ($db->schema->getTableSchema('test_timestamp_default_null') !== null) {
@@ -344,7 +345,7 @@ class SchemaTest extends \yiiunit\framework\db\SchemaTest
     /**
      * @see https://github.com/yiisoft/yii2/issues/20329
      */
-    public function testTimestampUtcNowDefaultValue()
+    public function testTimestampUtcNowDefaultValue(): void
     {
         $db = $this->getConnection(false);
         if ($db->schema->getTableSchema('test_timestamp_utc_now_default') !== null) {
@@ -364,7 +365,7 @@ class SchemaTest extends \yiiunit\framework\db\SchemaTest
     /**
      * @see https://github.com/yiisoft/yii2/issues/20329
      */
-    public function testTimestampNowDefaultValue()
+    public function testTimestampNowDefaultValue(): void
     {
         $db = $this->getConnection(false);
         if ($db->schema->getTableSchema('test_timestamp_now_default') !== null) {
@@ -384,7 +385,7 @@ class SchemaTest extends \yiiunit\framework\db\SchemaTest
     /**
      * @see https://github.com/yiisoft/yii2/issues/20329
      */
-    public function testTimestampUtcStringDefaultValue()
+    public function testTimestampUtcStringDefaultValue(): void
     {
         $db = $this->getConnection(false);
         if ($db->schema->getTableSchema('test_timestamp_utc_string_default') !== null) {
@@ -411,7 +412,7 @@ class SchemaTest extends \yiiunit\framework\db\SchemaTest
         return $result;
     }
 
-    public function testCustomTypeInNonDefaultSchema()
+    public function testCustomTypeInNonDefaultSchema(): void
     {
         $connection = $this->getConnection();
         ActiveRecord::$db = $this->getConnection();
diff --git a/tests/framework/db/pgsql/UniqueValidatorTest.php b/tests/framework/db/pgsql/UniqueValidatorTest.php
index df4817872d..d45480995f 100644
--- a/tests/framework/db/pgsql/UniqueValidatorTest.php
+++ b/tests/framework/db/pgsql/UniqueValidatorTest.php
@@ -20,7 +20,7 @@ class UniqueValidatorTest extends \yiiunit\framework\validators\UniqueValidatorT
 {
     public $driverName = 'pgsql';
 
-    public function testPrepareParams()
+    public function testPrepareParams(): void
     {
         parent::testPrepareParams();
 
diff --git a/tests/framework/db/pgsql/type/BooleanTest.php b/tests/framework/db/pgsql/type/BooleanTest.php
index 6d7e600f11..d4dcc4df19 100644
--- a/tests/framework/db/pgsql/type/BooleanTest.php
+++ b/tests/framework/db/pgsql/type/BooleanTest.php
@@ -19,7 +19,7 @@ class BooleanTest extends DatabaseTestCase
 {
     protected $driverName = 'pgsql';
 
-    public function testBoolean()
+    public function testBoolean(): void
     {
         $db = $this->getConnection(true);
         $schema = $db->getSchema();
@@ -60,7 +60,7 @@ class BooleanTest extends DatabaseTestCase
         $this->assertTrue($phpTypeCast);
     }
 
-    public function testBooleanWithValueInteger()
+    public function testBooleanWithValueInteger(): void
     {
         $db = $this->getConnection(true);
         $schema = $db->getSchema();
@@ -101,7 +101,7 @@ class BooleanTest extends DatabaseTestCase
         $this->assertTrue($phpTypeCast);
     }
 
-    public function testBooleanWithValueNegative()
+    public function testBooleanWithValueNegative(): void
     {
         $db = $this->getConnection(true);
         $schema = $db->getSchema();
@@ -133,7 +133,7 @@ class BooleanTest extends DatabaseTestCase
         $this->assertTrue($phpTypeCast);
     }
 
-    public function testBooleanWithValueNull()
+    public function testBooleanWithValueNull(): void
     {
         $db = $this->getConnection(true);
         $schema = $db->getSchema();
@@ -165,7 +165,7 @@ class BooleanTest extends DatabaseTestCase
         $this->assertNull($phpTypeCast);
     }
 
-    public function testBooleanWithValueOverflow()
+    public function testBooleanWithValueOverflow(): void
     {
         $db = $this->getConnection(true);
         $schema = $db->getSchema();
@@ -197,7 +197,7 @@ class BooleanTest extends DatabaseTestCase
         $this->assertTrue($phpTypeCast);
     }
 
-    public function testBooleanWithValueString()
+    public function testBooleanWithValueString(): void
     {
         $db = $this->getConnection(true);
         $schema = $db->getSchema();
diff --git a/tests/framework/db/sqlite/CommandTest.php b/tests/framework/db/sqlite/CommandTest.php
index ea31986b02..20ebbf789f 100644
--- a/tests/framework/db/sqlite/CommandTest.php
+++ b/tests/framework/db/sqlite/CommandTest.php
@@ -18,7 +18,7 @@ class CommandTest extends \yiiunit\framework\db\CommandTest
 {
     protected $driverName = 'sqlite';
 
-    public function testAutoQuoting()
+    public function testAutoQuoting(): void
     {
         $db = $this->getConnection(false);
 
@@ -32,7 +32,7 @@ class CommandTest extends \yiiunit\framework\db\CommandTest
      * @param array $firstData
      * @param array $secondData
      */
-    public function testUpsert(array $firstData, array $secondData)
+    public function testUpsert(array $firstData, array $secondData): void
     {
         if (version_compare($this->getConnection(false)->getServerVersion(), '3.8.3', '<')) {
             $this->markTestSkipped('SQLite < 3.8.3 does not support "WITH" keyword.');
@@ -42,27 +42,27 @@ class CommandTest extends \yiiunit\framework\db\CommandTest
         parent::testUpsert($firstData, $secondData);
     }
 
-    public function testAddDropPrimaryKey()
+    public function testAddDropPrimaryKey(): void
     {
         $this->markTestSkipped('SQLite does not support adding/dropping primary keys.');
     }
 
-    public function testAddDropForeignKey()
+    public function testAddDropForeignKey(): void
     {
         $this->markTestSkipped('SQLite does not support adding/dropping foreign keys.');
     }
 
-    public function testAddDropUnique()
+    public function testAddDropUnique(): void
     {
         $this->markTestSkipped('SQLite does not support adding/dropping unique constraints.');
     }
 
-    public function testAddDropCheck()
+    public function testAddDropCheck(): void
     {
         $this->markTestSkipped('SQLite does not support adding/dropping check constraints.');
     }
 
-    public function testMultiStatementSupport()
+    public function testMultiStatementSupport(): void
     {
         $db = $this->getConnection(false);
         $sql = <<<'SQL'
@@ -113,7 +113,7 @@ SQL;
         return $parent;
     }
 
-    public function testResetSequence()
+    public function testResetSequence(): void
     {
         $db = $this->getConnection();
 
@@ -151,7 +151,7 @@ SQL;
         $this->assertEquals(5, $db->createCommand('SELECT MAX([[id]]) FROM {{reset_sequence}}')->queryScalar());
     }
 
-    public function testResetSequenceExceptionTableNoExist()
+    public function testResetSequenceExceptionTableNoExist(): void
     {
         $this->expectException('yii\base\InvalidArgumentException');
         $this->expectExceptionMessage('Table not found: no_exist_table');
@@ -160,7 +160,7 @@ SQL;
         $db->createCommand()->resetSequence('no_exist_table', 5)->execute();
     }
 
-    public function testResetSequenceExceptionSquenceNoExist()
+    public function testResetSequenceExceptionSquenceNoExist(): void
     {
         $this->expectException('yii\base\InvalidArgumentException');
         $this->expectExceptionMessage("There is not sequence associated with table 'type'.");
diff --git a/tests/framework/db/sqlite/ConnectionTest.php b/tests/framework/db/sqlite/ConnectionTest.php
index 4b39055997..8874a23730 100644
--- a/tests/framework/db/sqlite/ConnectionTest.php
+++ b/tests/framework/db/sqlite/ConnectionTest.php
@@ -8,6 +8,8 @@
 
 namespace yiiunit\framework\db\sqlite;
 
+use Exception;
+use Yii;
 use yii\db\Connection;
 use yii\db\Transaction;
 use yiiunit\data\ar\ActiveRecord;
@@ -21,7 +23,7 @@ class ConnectionTest extends \yiiunit\framework\db\ConnectionTest
 {
     protected $driverName = 'sqlite';
 
-    public function testConstruct()
+    public function testConstruct(): void
     {
         $connection = $this->getConnection(false);
         $params = $this->database;
@@ -29,7 +31,7 @@ class ConnectionTest extends \yiiunit\framework\db\ConnectionTest
         $this->assertEquals($params['dsn'], $connection->dsn);
     }
 
-    public function testQuoteValue()
+    public function testQuoteValue(): void
     {
         $connection = $this->getConnection(false);
         $this->assertEquals(123, $connection->quoteValue(123));
@@ -37,7 +39,7 @@ class ConnectionTest extends \yiiunit\framework\db\ConnectionTest
         $this->assertEquals("'It''s interesting'", $connection->quoteValue("It's interesting"));
     }
 
-    public function testTransactionIsolation()
+    public function testTransactionIsolation(): void
     {
         $connection = $this->getConnection(true);
 
@@ -50,7 +52,7 @@ class ConnectionTest extends \yiiunit\framework\db\ConnectionTest
         $this->assertTrue(true); // No exceptions means test is passed.
     }
 
-    public function testMasterSlave()
+    public function testMasterSlave(): void
     {
         $counts = [[0, 2], [1, 2], [2, 2]];
 
@@ -104,7 +106,7 @@ class ConnectionTest extends \yiiunit\framework\db\ConnectionTest
         }
     }
 
-    public function testMastersShuffled()
+    public function testMastersShuffled(): void
     {
         $mastersCount = 2;
         $slavesCount = 2;
@@ -129,7 +131,7 @@ class ConnectionTest extends \yiiunit\framework\db\ConnectionTest
         $this->assertCount($slavesCount, $hit_slaves, 'all slaves hit');
     }
 
-    public function testMastersSequential()
+    public function testMastersSequential(): void
     {
         $mastersCount = 2;
         $slavesCount = 2;
@@ -155,16 +157,16 @@ class ConnectionTest extends \yiiunit\framework\db\ConnectionTest
         $this->assertCount($slavesCount, $hit_slaves, 'all slaves hit');
     }
 
-    public function testRestoreMasterAfterException()
+    public function testRestoreMasterAfterException(): void
     {
         $db = $this->prepareMasterSlave(1, 1);
         $this->assertTrue($db->enableSlaves);
         try {
             $db->useMaster(function (Connection $db) {
-                throw new \Exception('fail');
+                throw new Exception('fail');
             });
             $this->fail('Exception was caught somewhere');
-        } catch (\Exception $e) {
+        } catch (Exception $e) {
             // ok
         }
         $this->assertTrue($db->enableSlaves);
@@ -179,7 +181,7 @@ class ConnectionTest extends \yiiunit\framework\db\ConnectionTest
     {
         $databases = self::getParam('databases');
         $fixture = $databases[$this->driverName]['fixture'];
-        $basePath = \Yii::getAlias('@yiiunit/runtime');
+        $basePath = Yii::getAlias('@yiiunit/runtime');
 
         $config = [
             'class' => 'yii\db\Connection',
@@ -201,10 +203,10 @@ class ConnectionTest extends \yiiunit\framework\db\ConnectionTest
             $config['slaves'][] = $slave;
         }
 
-        return \Yii::createObject($config);
+        return Yii::createObject($config);
     }
 
-    public function testAliasDbPath()
+    public function testAliasDbPath(): void
     {
         $config = [
             'dsn' => 'sqlite:@yiiunit/runtime/yii2aliastest.sq3',
@@ -217,7 +219,7 @@ class ConnectionTest extends \yiiunit\framework\db\ConnectionTest
         $connection->close();
     }
 
-    public function testExceptionContainsRawQuery()
+    public function testExceptionContainsRawQuery(): void
     {
         $this->markTestSkipped('This test does not work on sqlite because preparing the failing query fails');
     }
diff --git a/tests/framework/db/sqlite/QueryBuilderTest.php b/tests/framework/db/sqlite/QueryBuilderTest.php
index 0f0889ac42..4c6f716a86 100644
--- a/tests/framework/db/sqlite/QueryBuilderTest.php
+++ b/tests/framework/db/sqlite/QueryBuilderTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\db\sqlite;
 
+use PDO;
 use yii\db\Query;
 use yii\db\Schema;
 use yii\db\sqlite\QueryBuilder;
@@ -53,12 +54,12 @@ class QueryBuilderTest extends \yiiunit\framework\db\QueryBuilderTest
         ]);
     }
 
-    public function primaryKeysProvider()
+    public function primaryKeysProvider(): void
     {
         $this->markTestSkipped('Adding/dropping primary keys is not supported in SQLite.');
     }
 
-    public function foreignKeysProvider()
+    public function foreignKeysProvider(): void
     {
         $this->markTestSkipped('Adding/dropping foreign keys is not supported in SQLite.');
     }
@@ -82,27 +83,27 @@ class QueryBuilderTest extends \yiiunit\framework\db\QueryBuilderTest
         return $result;
     }
 
-    public function uniquesProvider()
+    public function uniquesProvider(): void
     {
         $this->markTestSkipped('Adding/dropping unique constraints is not supported in SQLite.');
     }
 
-    public function checksProvider()
+    public function checksProvider(): void
     {
         $this->markTestSkipped('Adding/dropping check constraints is not supported in SQLite.');
     }
 
-    public function defaultValuesProvider()
+    public function defaultValuesProvider(): void
     {
         $this->markTestSkipped('Adding/dropping default constraints is not supported in SQLite.');
     }
 
-    public function testCommentColumn()
+    public function testCommentColumn(): void
     {
         $this->markTestSkipped('Comments are not supported in SQLite');
     }
 
-    public function testCommentTable()
+    public function testCommentTable(): void
     {
         $this->markTestSkipped('Comments are not supported in SQLite');
     }
@@ -114,17 +115,17 @@ class QueryBuilderTest extends \yiiunit\framework\db\QueryBuilderTest
         return $data;
     }
 
-    public function testBatchInsertOnOlderVersions()
+    public function testBatchInsertOnOlderVersions(): void
     {
         $db = $this->getConnection();
-        if (version_compare($db->pdo->getAttribute(\PDO::ATTR_SERVER_VERSION), '3.7.11', '>=')) {
+        if (version_compare($db->pdo->getAttribute(PDO::ATTR_SERVER_VERSION), '3.7.11', '>=')) {
             $this->markTestSkipped('This test is only relevant for SQLite < 3.7.11');
         }
         $sql = $this->getQueryBuilder()->batchInsert('{{customer}} t', ['t.id', 't.name'], [[1, 'a'], [2, 'b']]);
         $this->assertEquals("INSERT INTO {{customer}} t (`t`.`id`, `t`.`name`) SELECT 1, 'a' UNION SELECT 2, 'b'", $sql);
     }
 
-    public function testRenameTable()
+    public function testRenameTable(): void
     {
         $sql = $this->getQueryBuilder()->renameTable('table_from', 'table_to');
         $this->assertEquals('ALTER TABLE `table_from` RENAME TO `table_to`', $sql);
@@ -133,7 +134,7 @@ class QueryBuilderTest extends \yiiunit\framework\db\QueryBuilderTest
     /**
      * {@inheritdoc}
      */
-    public function testBuildUnion()
+    public function testBuildUnion(): void
     {
         $expectedQuerySql = $this->replaceQuotes(
             'SELECT `id` FROM `TotalExample` `t1` WHERE (w > 0) AND (x < 2) UNION  SELECT `id` FROM `TotalTotalExample` `t2` WHERE w > 5 UNION ALL  SELECT `id` FROM `TotalTotalExample` `t3` WHERE w = 3'
@@ -157,7 +158,7 @@ class QueryBuilderTest extends \yiiunit\framework\db\QueryBuilderTest
         $this->assertEquals([], $queryParams);
     }
 
-    public function testBuildWithQuery()
+    public function testBuildWithQuery(): void
     {
         $expectedQuerySql = $this->replaceQuotes(
             'WITH a1 AS (SELECT [[id]] FROM [[t1]] WHERE expr = 1), a2 AS (SELECT [[id]] FROM [[t2]] INNER JOIN [[a1]] ON t2.id = a1.id WHERE expr = 2 UNION  SELECT [[id]] FROM [[t3]] WHERE expr = 3) SELECT * FROM [[a2]]'
@@ -188,7 +189,7 @@ class QueryBuilderTest extends \yiiunit\framework\db\QueryBuilderTest
         $this->assertEquals([], $queryParams);
     }
 
-    public function testResetSequence()
+    public function testResetSequence(): void
     {
         $qb = $this->getQueryBuilder(true, true);
 
diff --git a/tests/framework/db/sqlite/QueryTest.php b/tests/framework/db/sqlite/QueryTest.php
index 67c5873960..47baf7f0e4 100644
--- a/tests/framework/db/sqlite/QueryTest.php
+++ b/tests/framework/db/sqlite/QueryTest.php
@@ -18,7 +18,7 @@ class QueryTest extends \yiiunit\framework\db\QueryTest
 {
     protected $driverName = 'sqlite';
 
-    public function testUnion()
+    public function testUnion(): void
     {
         $connection = $this->getConnection();
         $query = new Query();
diff --git a/tests/framework/db/sqlite/SchemaTest.php b/tests/framework/db/sqlite/SchemaTest.php
index b4ca70e685..2786e6c110 100644
--- a/tests/framework/db/sqlite/SchemaTest.php
+++ b/tests/framework/db/sqlite/SchemaTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\db\sqlite;
 
+use yii\base\NotSupportedException;
 use yii\db\Constraint;
 use yiiunit\framework\db\AnyValue;
 
@@ -19,7 +20,7 @@ class SchemaTest extends \yiiunit\framework\db\SchemaTest
 {
     protected $driverName = 'sqlite';
 
-    public function testGetSchemaNames()
+    public function testGetSchemaNames(): void
     {
         $this->markTestSkipped('Schemas are not supported in SQLite.');
     }
@@ -44,7 +45,7 @@ class SchemaTest extends \yiiunit\framework\db\SchemaTest
         return $columns;
     }
 
-    public function testCompositeFk()
+    public function testCompositeFk(): void
     {
         $schema = $this->getConnection()->schema;
 
@@ -88,9 +89,9 @@ class SchemaTest extends \yiiunit\framework\db\SchemaTest
      * @dataProvider quoteTableNameDataProvider
      * @param $name
      * @param $expectedName
-     * @throws \yii\base\NotSupportedException
+     * @throws NotSupportedException
      */
-    public function testQuoteTableName($name, $expectedName)
+    public function testQuoteTableName($name, $expectedName): void
     {
         $schema = $this->getConnection()->getSchema();
         $quotedName = $schema->quoteTableName($name);
diff --git a/tests/framework/db/sqlite/SqlTokenizerTest.php b/tests/framework/db/sqlite/SqlTokenizerTest.php
index e870f5e45e..f1acd34ef8 100644
--- a/tests/framework/db/sqlite/SqlTokenizerTest.php
+++ b/tests/framework/db/sqlite/SqlTokenizerTest.php
@@ -1122,7 +1122,7 @@ SELECT*from/*foo*/`T_constraints_1`WHERE not`C_check`=\'foo\'\'bar\'--bar
      * @dataProvider sqlProvider
      * @param string $sql
      */
-    public function testTokenizer($sql, SqlToken $expectedToken)
+    public function testTokenizer($sql, SqlToken $expectedToken): void
     {
         $actualToken = (new SqlTokenizer($sql))->tokenize();
         $this->assertEquals($expectedToken, $actualToken);
diff --git a/tests/framework/db/sqlite/type/BooleanTest.php b/tests/framework/db/sqlite/type/BooleanTest.php
index 128c4afb5e..c56a4efea4 100644
--- a/tests/framework/db/sqlite/type/BooleanTest.php
+++ b/tests/framework/db/sqlite/type/BooleanTest.php
@@ -19,7 +19,7 @@ class BooleanTest extends DatabaseTestCase
 {
     protected $driverName = 'sqlite';
 
-    public function testBoolean()
+    public function testBoolean(): void
     {
         $db = $this->getConnection(true);
         $schema = $db->getSchema();
@@ -72,7 +72,7 @@ class BooleanTest extends DatabaseTestCase
         $this->assertTrue($phpTypeCastBoolColBit);
     }
 
-    public function testBooleanWithValueInteger()
+    public function testBooleanWithValueInteger(): void
     {
         $db = $this->getConnection(true);
         $schema = $db->getSchema();
@@ -125,7 +125,7 @@ class BooleanTest extends DatabaseTestCase
         $this->assertTrue($phpTypeCastBoolColBit);
     }
 
-    public function testBooleanWithValueNegative()
+    public function testBooleanWithValueNegative(): void
     {
         $db = $this->getConnection(true);
         $schema = $db->getSchema();
@@ -166,7 +166,7 @@ class BooleanTest extends DatabaseTestCase
         $this->assertTrue($phpTypeCastBoolColBit);
     }
 
-    public function testBooleanWithValueNull()
+    public function testBooleanWithValueNull(): void
     {
         $db = $this->getConnection(true);
         $schema = $db->getSchema();
@@ -207,7 +207,7 @@ class BooleanTest extends DatabaseTestCase
         $this->assertNull($phpTypeCastBoolColBit);
     }
 
-    public function testBooleanWithValueOverflow()
+    public function testBooleanWithValueOverflow(): void
     {
         $db = $this->getConnection(true);
         $schema = $db->getSchema();
diff --git a/tests/framework/db/testBatchInsertWithYield.php b/tests/framework/db/testBatchInsertWithYield.php
index 26548156a0..840ea2f8d8 100644
--- a/tests/framework/db/testBatchInsertWithYield.php
+++ b/tests/framework/db/testBatchInsertWithYield.php
@@ -1,13 +1,14 @@
 <?php
 
+use yiiunit\framework\db\CommandTest;
+
 /**
  * @link https://www.yiiframework.com/
  * @copyright Copyright (c) 2008 Yii Software LLC
  * @license https://www.yiiframework.com/license/
  *
- * @var \yiiunit\framework\db\CommandTest $this
+ * @var CommandTest $this
  */
-
 $rows = call_user_func(function () {
     if (false) {
         yield [];
diff --git a/tests/framework/di/ContainerTest.php b/tests/framework/di/ContainerTest.php
index a9be315687..d687ed7590 100644
--- a/tests/framework/di/ContainerTest.php
+++ b/tests/framework/di/ContainerTest.php
@@ -8,6 +8,11 @@
 
 namespace yiiunit\framework\di;
 
+use yii\console\Request;
+use yii\console\Response;
+use Exception;
+use yii\di\NotInstantiableException;
+use yii\web\Application;
 use Yii;
 use yii\di\Container;
 use yii\di\Instance;
@@ -47,7 +52,7 @@ class ContainerTest extends TestCase
         Yii::$container = new Container();
     }
 
-    public function testDefault()
+    public function testDefault(): void
     {
         $namespace = __NAMESPACE__ . '\stubs';
         $QuxInterface = "$namespace\\QuxInterface";
@@ -140,7 +145,7 @@ class ContainerTest extends TestCase
         $this->assertEquals(4, $qux->a);
     }
 
-    public function testInvoke()
+    public function testInvoke(): void
     {
         $this->mockApplication([
             'components' => [
@@ -160,21 +165,21 @@ class ContainerTest extends TestCase
         ]);
 
         // use component of application
-        $callback = function ($param, stubs\QuxInterface $qux, Bar $bar) {
+        $callback = function ($param, QuxInterface $qux, Bar $bar) {
             return [$param, $qux instanceof Qux, $qux->a, $bar->qux->a];
         };
         $result = Yii::$container->invoke($callback, ['D426']);
         $this->assertEquals(['D426', true, 'belongApp', 'independent'], $result);
 
         // another component of application
-        $callback = function ($param, stubs\QuxInterface $qux2, $other = 'default') {
+        $callback = function ($param, QuxInterface $qux2, $other = 'default') {
             return [$param, $qux2 instanceof Qux, $qux2->a, $other];
         };
         $result = Yii::$container->invoke($callback, ['M2792684']);
         $this->assertEquals(['M2792684', true, 'belongAppQux2', 'default'], $result);
 
         // component not belong application
-        $callback = function ($param, stubs\QuxInterface $notBelongApp, $other) {
+        $callback = function ($param, QuxInterface $notBelongApp, $other) {
             return [$param, $notBelongApp instanceof Qux, $notBelongApp->a, $other];
         };
         $result = Yii::$container->invoke($callback, ['MDM', 'not_default']);
@@ -198,7 +203,7 @@ class ContainerTest extends TestCase
         $this->assertFalse(Yii::$container->invoke(['yii\helpers\ArrayHelper', 'isAssociative'], [$array]));
 
 
-        $myFunc = function (\yii\console\Request $request, \yii\console\Response $response) {
+        $myFunc = function (Request $request, Response $response) {
             return [$request, $response];
         };
         list($request, $response) = Yii::$container->invoke($myFunc);
@@ -206,7 +211,7 @@ class ContainerTest extends TestCase
         $this->assertEquals($response, Yii::$app->response);
     }
 
-    public function testAssociativeInvoke()
+    public function testAssociativeInvoke(): void
     {
         $this->mockApplication([
             'components' => [
@@ -227,7 +232,7 @@ class ContainerTest extends TestCase
         $this->assertTrue(Yii::$container->invoke($closure, ['b' => 1, 'a' => 5]));
     }
 
-    public function testResolveCallableDependencies()
+    public function testResolveCallableDependencies(): void
     {
         $this->mockApplication([
             'components' => [
@@ -249,7 +254,7 @@ class ContainerTest extends TestCase
         $this->assertEquals([1, 5], Yii::$container->resolveCallableDependencies($closure, [1, 5]));
     }
 
-    public function testOptionalDependencies()
+    public function testOptionalDependencies(): void
     {
         $container = new Container();
         // Test optional unresolvable dependency.
@@ -259,7 +264,7 @@ class ContainerTest extends TestCase
         $this->assertNull($container->invoke($closure));
     }
 
-    public function testSetDependencies()
+    public function testSetDependencies(): void
     {
         $container = new Container();
         $container->setDefinitions([
@@ -289,12 +294,12 @@ class ContainerTest extends TestCase
         try {
             $container->get('rollbar');
             $this->fail('InvalidConfigException was not thrown');
-        } catch (\Exception $e) {
+        } catch (Exception $e) {
             $this->assertInstanceOf('yii\base\InvalidConfigException', $e);
         }
     }
 
-    public function testStaticCall()
+    public function testStaticCall(): void
     {
         $container = new Container();
         $container->setDefinitions([
@@ -306,7 +311,7 @@ class ContainerTest extends TestCase
         $this->assertSame(42, $qux->a);
     }
 
-    public function testObject()
+    public function testObject(): void
     {
         $container = new Container();
         $container->setDefinitions([
@@ -318,7 +323,7 @@ class ContainerTest extends TestCase
         $this->assertSame(42, $qux->a);
     }
 
-    public function testDi3Compatibility()
+    public function testDi3Compatibility(): void
     {
         $container = new Container();
         $container->setDefinitions([
@@ -341,7 +346,7 @@ class ContainerTest extends TestCase
         $this->assertEquals('item1', $traversable->current());
     }
 
-    public function testInstanceOf()
+    public function testInstanceOf(): void
     {
         $container = new Container();
         $container->setDefinitions([
@@ -363,7 +368,7 @@ class ContainerTest extends TestCase
         $this->assertSame(42, $qux->a);
     }
 
-    public function testReferencesInArrayInDependencies()
+    public function testReferencesInArrayInDependencies(): void
     {
         $quxInterface = 'yiiunit\framework\di\stubs\QuxInterface';
         $container = new Container();
@@ -401,7 +406,7 @@ class ContainerTest extends TestCase
         $this->assertSame(33, $q33->a);
     }
 
-    public function testGetByInstance()
+    public function testGetByInstance(): void
     {
         $container = new Container();
         $container->setSingletons([
@@ -416,7 +421,7 @@ class ContainerTest extends TestCase
         $this->assertSame($one, $container->get('two'));
     }
 
-    public function testWithoutDefinition()
+    public function testWithoutDefinition(): void
     {
         $container = new Container();
 
@@ -429,7 +434,7 @@ class ContainerTest extends TestCase
         $this->assertNotSame($one, $two);
     }
 
-    public function testGetByClassIndirectly()
+    public function testGetByClassIndirectly(): void
     {
         $container = new Container();
         $container->setSingletons([
@@ -444,15 +449,15 @@ class ContainerTest extends TestCase
         $this->assertSame(42, $qux->a);
     }
 
-    public function testThrowingNotFoundException()
+    public function testThrowingNotFoundException(): void
     {
-        $this->expectException(\yii\di\NotInstantiableException::class);
+        $this->expectException(NotInstantiableException::class);
 
         $container = new Container();
         $container->get('non_existing');
     }
 
-    public function testContainerSingletons()
+    public function testContainerSingletons(): void
     {
         $container = new Container();
         $container->setSingletons([
@@ -480,7 +485,7 @@ class ContainerTest extends TestCase
         $this->assertSame($foo, $sameFoo);
     }
 
-    public function testVariadicConstructor()
+    public function testVariadicConstructor(): void
     {
         if (\defined('HHVM_VERSION')) {
             static::markTestSkipped('Can not test on HHVM because it does not support variadics.');
@@ -492,7 +497,7 @@ class ContainerTest extends TestCase
         $this->assertTrue(true);
     }
 
-    public function testVariadicCallable()
+    public function testVariadicCallable(): void
     {
         if (\defined('HHVM_VERSION')) {
             static::markTestSkipped('Can not test on HHVM because it does not support variadics.');
@@ -506,7 +511,7 @@ class ContainerTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/18245
      */
-    public function testDelayedInitializationOfSubArray()
+    public function testDelayedInitializationOfSubArray(): void
     {
         $definitions = [
             'test' => [
@@ -518,7 +523,7 @@ class ContainerTest extends TestCase
         ];
 
         $application = Yii::createObject([
-            '__class' => \yii\web\Application::className(),
+            '__class' => Application::className(),
             'basePath' => __DIR__,
             'id' => 'test',
             'components' => [
@@ -540,7 +545,7 @@ class ContainerTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/18304
      */
-    public function testNulledConstructorParameters()
+    public function testNulledConstructorParameters(): void
     {
         $alpha = (new Container())->get(Alpha::className());
         $this->assertInstanceOf(Beta::className(), $alpha->beta);
@@ -564,7 +569,7 @@ class ContainerTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/18284
      */
-    public function testNamedConstructorParameters()
+    public function testNamedConstructorParameters(): void
     {
         $test = (new Container())->get(Car::className(), [
             'name' => 'Hello',
@@ -577,7 +582,7 @@ class ContainerTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/18284
      */
-    public function testInvalidConstructorParameters()
+    public function testInvalidConstructorParameters(): void
     {
         $this->expectException('yii\base\InvalidConfigException');
         $this->expectExceptionMessage('Dependencies indexed by name and by position in the same array are not allowed.');
@@ -602,13 +607,13 @@ class ContainerTest extends TestCase
      *
      * @param string $class
      */
-    public function testNotInstantiableException($class)
+    public function testNotInstantiableException($class): void
     {
         $this->expectException('yii\di\NotInstantiableException');
         (new Container())->get($class);
     }
 
-    public function testNullTypeConstructorParameters()
+    public function testNullTypeConstructorParameters(): void
     {
         $zeta = (new Container())->get(Zeta::className());
         $this->assertInstanceOf(Beta::className(), $zeta->beta);
@@ -621,7 +626,7 @@ class ContainerTest extends TestCase
         $this->assertNull($zeta->unknownNull);
     }
 
-    public function testUnionTypeWithNullConstructorParameters()
+    public function testUnionTypeWithNullConstructorParameters(): void
     {
         if (PHP_VERSION_ID < 80000) {
             $this->markTestSkipped('Can not be tested on PHP < 8.0');
@@ -632,7 +637,7 @@ class ContainerTest extends TestCase
         $this->assertInstanceOf(UnionTypeNull::className(), $unionType);
     }
 
-    public function testUnionTypeWithoutNullConstructorParameters()
+    public function testUnionTypeWithoutNullConstructorParameters(): void
     {
         if (PHP_VERSION_ID < 80000) {
             $this->markTestSkipped('Can not be tested on PHP < 8.0');
@@ -655,7 +660,7 @@ class ContainerTest extends TestCase
         (new Container())->get(UnionTypeNotNull::className());
     }
 
-    public function testUnionTypeWithClassConstructorParameters()
+    public function testUnionTypeWithClassConstructorParameters(): void
     {
         if (PHP_VERSION_ID < 80000) {
             $this->markTestSkipped('Can not be tested on PHP < 8.0');
@@ -670,7 +675,7 @@ class ContainerTest extends TestCase
         (new Container())->get(UnionTypeNotNull::className());
     }
 
-    public function testResolveCallableDependenciesUnionTypes()
+    public function testResolveCallableDependenciesUnionTypes(): void
     {
         if (PHP_VERSION_ID < 80000) {
             $this->markTestSkipped('Can not be tested on PHP < 8.0');
@@ -702,7 +707,7 @@ class ContainerTest extends TestCase
         $this->assertInstanceOf(Qux::classname(), $params[0]);
     }
 
-    public function testResolveCallableDependenciesIntersectionTypes()
+    public function testResolveCallableDependenciesIntersectionTypes(): void
     {
         if (PHP_VERSION_ID < 80100) {
             $this->markTestSkipped('Can not be tested on PHP < 8.1');
diff --git a/tests/framework/di/InstanceTest.php b/tests/framework/di/InstanceTest.php
index 14483d922f..beb2574b93 100644
--- a/tests/framework/di/InstanceTest.php
+++ b/tests/framework/di/InstanceTest.php
@@ -28,7 +28,7 @@ class InstanceTest extends TestCase
         Yii::$container = new Container();
     }
 
-    public function testOf()
+    public function testOf(): void
     {
         $container = new Container();
         $className = Component::className();
@@ -40,7 +40,7 @@ class InstanceTest extends TestCase
         $this->assertNotSame($instance->get($container), Instance::ensure($instance, $className, $container));
     }
 
-    public function testEnsure()
+    public function testEnsure(): void
     {
         $container = new Container();
         $container->set('db', [
@@ -57,7 +57,7 @@ class InstanceTest extends TestCase
     /**
      * ensure an InvalidConfigException is thrown when a component does not exist.
      */
-    public function testEnsure_NonExistingComponentException()
+    public function testEnsure_NonExistingComponentException(): void
     {
         $container = new Container();
         $this->expectException('yii\base\InvalidConfigException');
@@ -68,7 +68,7 @@ class InstanceTest extends TestCase
     /**
      * ensure an InvalidConfigException is thrown when a class does not exist.
      */
-    public function testEnsure_NonExistingClassException()
+    public function testEnsure_NonExistingClassException(): void
     {
         $container = new Container();
         $this->expectException('yii\base\InvalidConfigException');
@@ -76,7 +76,7 @@ class InstanceTest extends TestCase
         Instance::ensure('yii\cache\DoesNotExist', 'yii\cache\Cache', $container);
     }
 
-    public function testEnsure_WithoutType()
+    public function testEnsure_WithoutType(): void
     {
         $container = new Container();
         $container->set('db', [
@@ -89,7 +89,7 @@ class InstanceTest extends TestCase
         $this->assertInstanceOf('\\yii\\db\\Connection', Instance::ensure(['class' => 'yii\db\Connection', 'dsn' => 'test'], null, $container));
     }
 
-    public function testEnsure_MinimalSettings()
+    public function testEnsure_MinimalSettings(): void
     {
         Yii::$container->set('db', [
             'class' => 'yii\db\Connection',
@@ -103,7 +103,7 @@ class InstanceTest extends TestCase
         Yii::$container = new Container();
     }
 
-    public function testExceptionRefersTo()
+    public function testExceptionRefersTo(): void
     {
         $container = new Container();
         $container->set('db', [
@@ -117,21 +117,21 @@ class InstanceTest extends TestCase
         Instance::ensure('db', 'yii\base\Widget', $container);
     }
 
-    public function testExceptionInvalidDataType()
+    public function testExceptionInvalidDataType(): void
     {
         $this->expectException('yii\base\InvalidConfigException');
         $this->expectExceptionMessage('Invalid data type: yii\db\Connection. yii\base\Widget is expected.');
         Instance::ensure(new Connection(), 'yii\base\Widget');
     }
 
-    public function testExceptionComponentIsNotSpecified()
+    public function testExceptionComponentIsNotSpecified(): void
     {
         $this->expectException('yii\base\InvalidConfigException');
         $this->expectExceptionMessage('The required component is not specified.');
         Instance::ensure('');
     }
 
-    public function testGet()
+    public function testGet(): void
     {
         $this->mockApplication([
             'components' => [
@@ -152,7 +152,7 @@ class InstanceTest extends TestCase
     /**
      * This tests the usage example given in yii\di\Instance class PHPDoc.
      */
-    public function testLazyInitializationExample()
+    public function testLazyInitializationExample(): void
     {
         Yii::$container = new Container();
         Yii::$container->set('cache', [
@@ -169,7 +169,7 @@ class InstanceTest extends TestCase
         $this->assertEquals('sqlite:path/to/file.db', $db->dsn);
     }
 
-    public function testRestoreAfterVarExport()
+    public function testRestoreAfterVarExport(): void
     {
         $instance = Instance::of('something');
         $export = var_export($instance, true);
@@ -184,7 +184,7 @@ class InstanceTest extends TestCase
         ]));
     }
 
-    public function testRestoreAfterVarExportRequiresId()
+    public function testRestoreAfterVarExportRequiresId(): void
     {
         $this->expectException('yii\base\InvalidConfigException');
         $this->expectExceptionMessage('Failed to instantiate class "Instance". Required parameter "id" is missing');
@@ -192,7 +192,7 @@ class InstanceTest extends TestCase
         Instance::__set_state([]);
     }
 
-    public function testExceptionInvalidDataTypeInArray()
+    public function testExceptionInvalidDataTypeInArray(): void
     {
         $this->expectException('yii\base\InvalidConfigException');
         $this->expectExceptionMessage('Invalid data type: yii\db\Connection. yii\base\Widget is expected.');
diff --git a/tests/framework/di/ServiceLocatorTest.php b/tests/framework/di/ServiceLocatorTest.php
index f3c1fdfb00..5e70ddee35 100644
--- a/tests/framework/di/ServiceLocatorTest.php
+++ b/tests/framework/di/ServiceLocatorTest.php
@@ -37,7 +37,7 @@ class TestSubclass extends TestClass
  */
 class ServiceLocatorTest extends TestCase
 {
-    public function testCallable()
+    public function testCallable(): void
     {
         // anonymous function
         $container = new ServiceLocator();
@@ -63,7 +63,7 @@ class ServiceLocatorTest extends TestCase
         $this->assertNull($object->prop2);
     }
 
-    public function testObject()
+    public function testObject(): void
     {
         $object = new TestClass();
         $className = TestClass::className();
@@ -72,7 +72,7 @@ class ServiceLocatorTest extends TestCase
         $this->assertSame($container->get($className), $object);
     }
 
-    public function testDi3Compatibility()
+    public function testDi3Compatibility(): void
     {
         $config = [
             'components' => [
@@ -89,7 +89,7 @@ class ServiceLocatorTest extends TestCase
         $this->assertInstanceOf(TestSubclass::className(), $app->get('test'));
     }
 
-    public function testShared()
+    public function testShared(): void
     {
         // with configuration: shared
         $container = new ServiceLocator();
@@ -112,7 +112,7 @@ class ServiceLocatorTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/11771
      */
-    public function testModulePropertyIsset()
+    public function testModulePropertyIsset(): void
     {
         $config = [
             'components' => [
diff --git a/tests/framework/di/stubs/BarSetter.php b/tests/framework/di/stubs/BarSetter.php
index c45b3b3cf8..858b943141 100644
--- a/tests/framework/di/stubs/BarSetter.php
+++ b/tests/framework/di/stubs/BarSetter.php
@@ -34,7 +34,7 @@ class BarSetter extends BaseObject
     /**
      * @param mixed $qux
      */
-    public function setQux(QuxInterface $qux)
+    public function setQux(QuxInterface $qux): void
     {
         $this->qux = $qux;
     }
diff --git a/tests/framework/di/stubs/FooBaz.php b/tests/framework/di/stubs/FooBaz.php
index cc4426f511..ab1312de1e 100644
--- a/tests/framework/di/stubs/FooBaz.php
+++ b/tests/framework/di/stubs/FooBaz.php
@@ -8,23 +8,26 @@
 
 namespace yiiunit\framework\di\stubs;
 
+use yii\base\BaseObject;
+use Yii;
+
 /**
  * @author Yusup Hambali <supalpuket@gmail.com>
  * @since 2.0.31
  */
-class FooBaz extends \yii\base\BaseObject
+class FooBaz extends BaseObject
 {
     public $fooDependent = [];
 
-    public function init()
+    public function init(): void
     {
         // default config usually used by Yii
         $dependentConfig = array_merge(['class' => FooDependent::className()], $this->fooDependent);
-        $this->fooDependent = \Yii::createObject($dependentConfig);
+        $this->fooDependent = Yii::createObject($dependentConfig);
     }
 }
 
-class FooDependent extends \yii\base\BaseObject
+class FooDependent extends BaseObject
 {
 }
 
diff --git a/tests/framework/di/stubs/QuxFactory.php b/tests/framework/di/stubs/QuxFactory.php
index 1cee9798cf..43d377fe8d 100644
--- a/tests/framework/di/stubs/QuxFactory.php
+++ b/tests/framework/di/stubs/QuxFactory.php
@@ -8,9 +8,10 @@
 
 namespace yiiunit\framework\di\stubs;
 
+use yii\base\BaseObject;
 use yii\di\Container;
 
-class QuxFactory extends \yii\base\BaseObject
+class QuxFactory extends BaseObject
 {
     public static function create(Container $container)
     {
diff --git a/tests/framework/filters/AccessRuleTest.php b/tests/framework/filters/AccessRuleTest.php
index 243db417f6..ac1ae38d3f 100644
--- a/tests/framework/filters/AccessRuleTest.php
+++ b/tests/framework/filters/AccessRuleTest.php
@@ -8,6 +8,8 @@
 
 namespace yiiunit\framework\filters;
 
+use yiiunit\TestCase;
+use yii\rbac\BaseManager;
 use Closure;
 use Yii;
 use yii\base\Action;
@@ -22,7 +24,7 @@ use yiiunit\framework\rbac\AuthorRule;
 /**
  * @group filters
  */
-class AccessRuleTest extends \yiiunit\TestCase
+class AccessRuleTest extends TestCase
 {
     protected function setUp(): void
     {
@@ -76,7 +78,7 @@ class AccessRuleTest extends \yiiunit\TestCase
     }
 
     /**
-     * @return \yii\rbac\BaseManager
+     * @return BaseManager
      */
     protected function mockAuthManager()
     {
@@ -121,7 +123,7 @@ class AccessRuleTest extends \yiiunit\TestCase
         return $auth;
     }
 
-    public function testMatchAction()
+    public function testMatchAction(): void
     {
         $action = $this->mockAction();
         $user = false;
@@ -149,7 +151,7 @@ class AccessRuleTest extends \yiiunit\TestCase
         $this->assertNull($rule->allows($action, $user, $request));
     }
 
-    public function testMatchController()
+    public function testMatchController(): void
     {
         $action = $this->mockAction();
         $user = false;
@@ -181,7 +183,7 @@ class AccessRuleTest extends \yiiunit\TestCase
     /**
      * @depends testMatchController
      */
-    public function testMatchControllerWildcard()
+    public function testMatchControllerWildcard(): void
     {
         $action = $this->mockAction();
         $user = false;
@@ -310,7 +312,7 @@ class AccessRuleTest extends \yiiunit\TestCase
      * @param array|Closure $roleParams params for $roleParams
      * @param bool $expected the expected result or null
      */
-    public function testMatchRole($actionid, $allow, $userid, $roleParams, $expected)
+    public function testMatchRole($actionid, $allow, $userid, $roleParams, $expected): void
     {
         $action = $this->mockAction();
         $auth = $this->mockAuthManager();
@@ -335,7 +337,7 @@ class AccessRuleTest extends \yiiunit\TestCase
      *
      * @see https://github.com/yiisoft/yii2/issues/4793
      */
-    public function testMatchRoleWithoutUser()
+    public function testMatchRoleWithoutUser(): void
     {
         $action = $this->mockAction();
         $request = $this->mockRequest();
@@ -349,7 +351,7 @@ class AccessRuleTest extends \yiiunit\TestCase
         $rule->allows($action, false, $request);
     }
 
-    public function testMatchRoleSpecial()
+    public function testMatchRoleSpecial(): void
     {
         $action = $this->mockAction();
         $request = $this->mockRequest();
@@ -375,7 +377,7 @@ class AccessRuleTest extends \yiiunit\TestCase
         $this->assertTrue($rule->allows($action, $guest, $request));
     }
 
-    public function testMatchRolesAndPermissions()
+    public function testMatchRolesAndPermissions(): void
     {
         $action = $this->mockAction();
         $user = $this->getMockBuilder('\yii\web\User')->getMock();
@@ -415,7 +417,7 @@ class AccessRuleTest extends \yiiunit\TestCase
     /**
      * Test that callable object can be used as roleParams values
      */
-    public function testMatchRoleWithRoleParamsCallable()
+    public function testMatchRoleWithRoleParamsCallable(): void
     {
         $action = $this->mockAction();
         $action->id = 'update';
@@ -436,7 +438,7 @@ class AccessRuleTest extends \yiiunit\TestCase
         $this->assertEquals(true, $rule->allows($action, $user, $request));
     }
 
-    public function testMatchVerb()
+    public function testMatchVerb(): void
     {
         $action = $this->mockAction();
         $user = false;
@@ -467,7 +469,7 @@ class AccessRuleTest extends \yiiunit\TestCase
 
     // TODO test match custom callback
 
-    public function testMatchIP()
+    public function testMatchIP(): void
     {
         $action = $this->mockAction();
         $user = false;
@@ -567,7 +569,7 @@ class AccessRuleTest extends \yiiunit\TestCase
         $this->assertNull($rule->allows($action, $user, $request));
     }
 
-    public function testMatchIPWildcard()
+    public function testMatchIPWildcard(): void
     {
         $action = $this->mockAction();
         $user = false;
@@ -611,7 +613,7 @@ class AccessRuleTest extends \yiiunit\TestCase
         $this->assertNull($rule->allows($action, $user, $request));
     }
 
-    public function testMatchIPMask()
+    public function testMatchIPMask(): void
     {
         $action = $this->mockAction();
         $user = false;
diff --git a/tests/framework/filters/AjaxFilterTest.php b/tests/framework/filters/AjaxFilterTest.php
index b15efe59d6..19fb045d0d 100644
--- a/tests/framework/filters/AjaxFilterTest.php
+++ b/tests/framework/filters/AjaxFilterTest.php
@@ -35,7 +35,7 @@ class AjaxFilterTest extends TestCase
         return $request;
     }
 
-    public function testFilter()
+    public function testFilter(): void
     {
         $this->mockWebApplication();
         $controller = new Controller('id', Yii::$app);
diff --git a/tests/framework/filters/ContentNegotiatorTest.php b/tests/framework/filters/ContentNegotiatorTest.php
index 3365e78292..79df9402ce 100644
--- a/tests/framework/filters/ContentNegotiatorTest.php
+++ b/tests/framework/filters/ContentNegotiatorTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\filters;
 
+use yii\web\BadRequestHttpException;
 use Yii;
 use yii\base\Action;
 use yii\filters\ContentNegotiator;
@@ -39,7 +40,7 @@ class ContentNegotiatorTest extends TestCase
         return [$action, $filter];
     }
 
-    public function testWhenLanguageGETParamIsArray()
+    public function testWhenLanguageGETParamIsArray(): void
     {
         list($action, $filter) = $this->mockActionAndFilter();
 
@@ -56,7 +57,7 @@ class ContentNegotiatorTest extends TestCase
         $this->assertEquals($targetLanguage, Yii::$app->language);
     }
 
-    public function testWhenFormatGETParamIsArray()
+    public function testWhenFormatGETParamIsArray(): void
     {
         list($action, $filter) = $this->mockActionAndFilter();
 
@@ -71,13 +72,13 @@ class ContentNegotiatorTest extends TestCase
             'application/xml' => Response::FORMAT_XML,
         ];
 
-        $this->expectException(\yii\web\BadRequestHttpException::class);
+        $this->expectException(BadRequestHttpException::class);
         $this->expectExceptionMessage('Invalid data received for GET parameter');
 
         $filter->beforeAction($action);
     }
 
-    public function testVaryHeader()
+    public function testVaryHeader(): void
     {
         list($action, $filter) = $this->mockActionAndFilter();
         $filter->formats = [];
@@ -118,7 +119,7 @@ class ContentNegotiatorTest extends TestCase
         $this->assertContains('Accept-Language', $varyHeader);
     }
 
-    public function testNegotiateContentType()
+    public function testNegotiateContentType(): void
     {
         $filter = new ContentNegotiator([
             'formats' => [
diff --git a/tests/framework/filters/CorsTest.php b/tests/framework/filters/CorsTest.php
index 6e73d01508..67c714b552 100644
--- a/tests/framework/filters/CorsTest.php
+++ b/tests/framework/filters/CorsTest.php
@@ -20,7 +20,7 @@ use yiiunit\TestCase;
  */
 class CorsTest extends TestCase
 {
-    public function testPreflight()
+    public function testPreflight(): void
     {
         $this->mockWebApplication();
         $controller = new Controller('id', Yii::$app);
@@ -43,7 +43,7 @@ class CorsTest extends TestCase
         $this->assertTrue($cors->beforeAction($action));
     }
 
-    public function testWildcardOrigin()
+    public function testWildcardOrigin(): void
     {
         $this->mockWebApplication();
         $controller = new Controller('id', Yii::$app);
@@ -64,7 +64,7 @@ class CorsTest extends TestCase
         $this->assertEquals('*', $cors->response->getHeaders()->get('access-control-allow-origin'));
     }
 
-    public function testAccessControlAllowHeadersPreflight()
+    public function testAccessControlAllowHeadersPreflight(): void
     {
         $this->mockWebApplication();
         $controller = new Controller('id', Yii::$app);
diff --git a/tests/framework/filters/HostControlTest.php b/tests/framework/filters/HostControlTest.php
index 9ae7a8207a..9435f51e73 100644
--- a/tests/framework/filters/HostControlTest.php
+++ b/tests/framework/filters/HostControlTest.php
@@ -90,7 +90,7 @@ class HostControlTest extends TestCase
      * @param string $host
      * @param bool $allowed
      */
-    public function testFilter($allowedHosts, $host, $allowed)
+    public function testFilter($allowedHosts, $host, $allowed): void
     {
         $_SERVER['HTTP_HOST'] = $host;
 
@@ -123,7 +123,7 @@ class HostControlTest extends TestCase
 
     public $denyCallBackCalled = false;
 
-    public function testDenyCallback()
+    public function testDenyCallback(): void
     {
         $filter = new HostControl();
         $filter->allowedHosts = ['example.com'];
@@ -138,7 +138,7 @@ class HostControlTest extends TestCase
         $this->assertTrue($this->denyCallBackCalled, 'denyCallback should have been called.');
     }
 
-    public function testDefaultHost()
+    public function testDefaultHost(): void
     {
         $filter = new HostControl();
         $filter->allowedHosts = ['example.com'];
@@ -153,7 +153,7 @@ class HostControlTest extends TestCase
         $this->assertSame('yiiframework.com', Yii::$app->getRequest()->getHostName());
     }
 
-    public function testErrorHandlerWithDefaultHost()
+    public function testErrorHandlerWithDefaultHost(): void
     {
         $this->expectException('yii\web\NotFoundHttpException');
         $this->expectExceptionMessage('Page not found.');
diff --git a/tests/framework/filters/HttpCacheTest.php b/tests/framework/filters/HttpCacheTest.php
index 20a235be49..93cf492591 100644
--- a/tests/framework/filters/HttpCacheTest.php
+++ b/tests/framework/filters/HttpCacheTest.php
@@ -8,13 +8,15 @@
 
 namespace yiiunit\framework\filters;
 
+use yiiunit\TestCase;
+use ReflectionMethod;
 use Yii;
 use yii\filters\HttpCache;
 
 /**
  * @group filters
  */
-class HttpCacheTest extends \yiiunit\TestCase
+class HttpCacheTest extends TestCase
 {
     protected function setUp(): void
     {
@@ -26,7 +28,7 @@ class HttpCacheTest extends \yiiunit\TestCase
         $this->mockWebApplication();
     }
 
-    public function testDisabled()
+    public function testDisabled(): void
     {
         $httpCache = new HttpCache();
         $this->assertTrue($httpCache->beforeAction(null));
@@ -34,7 +36,7 @@ class HttpCacheTest extends \yiiunit\TestCase
         $this->assertTrue($httpCache->beforeAction(null));
     }
 
-    public function testEmptyPragma()
+    public function testEmptyPragma(): void
     {
         $httpCache = new HttpCache();
         $httpCache->etagSeed = function ($action, $params) {
@@ -49,11 +51,11 @@ class HttpCacheTest extends \yiiunit\TestCase
     /**
      * @covers \yii\filters\HttpCache::validateCache
      */
-    public function testValidateCache()
+    public function testValidateCache(): void
     {
         $httpCache = new HttpCache();
         $request = Yii::$app->getRequest();
-        $method = new \ReflectionMethod($httpCache, 'validateCache');
+        $method = new ReflectionMethod($httpCache, 'validateCache');
 
         // @link https://wiki.php.net/rfc/deprecations_php_8_5#deprecate_reflectionsetaccessible
         // @link https://wiki.php.net/rfc/make-reflection-setaccessible-no-op
@@ -86,7 +88,7 @@ class HttpCacheTest extends \yiiunit\TestCase
     /**
      * @covers \yii\filters\HttpCache::generateEtag
      */
-    public function testGenerateEtag()
+    public function testGenerateEtag(): void
     {
         $httpCache = new HttpCache();
         $httpCache->weakEtag = false;
diff --git a/tests/framework/filters/PageCacheTest.php b/tests/framework/filters/PageCacheTest.php
index df281366ab..ea4f5f0c12 100644
--- a/tests/framework/filters/PageCacheTest.php
+++ b/tests/framework/filters/PageCacheTest.php
@@ -151,7 +151,7 @@ class PageCacheTest extends TestCase
      * @dataProvider cacheTestCaseProvider
      * @param array $testCase
      */
-    public function testCache($testCase)
+    public function testCache($testCase): void
     {
         $testCase = ArrayHelper::merge([
             'properties' => [],
@@ -255,7 +255,7 @@ class PageCacheTest extends TestCase
         }
     }
 
-    public function testExpired()
+    public function testExpired(): void
     {
         CacheTestCase::$time = time();
         CacheTestCase::$microtime = microtime(true);
@@ -300,7 +300,7 @@ class PageCacheTest extends TestCase
         ob_end_clean();
     }
 
-    public function testVaryByRoute()
+    public function testVaryByRoute(): void
     {
         $testCases = [
             false,
@@ -351,7 +351,7 @@ class PageCacheTest extends TestCase
         }
     }
 
-    public function testVariations()
+    public function testVariations(): void
     {
         $testCases = [
             [true, 'name' => 'value'],
@@ -403,7 +403,7 @@ class PageCacheTest extends TestCase
         }
     }
 
-    public function testDependency()
+    public function testDependency(): void
     {
         $testCases = [
             false,
@@ -460,7 +460,7 @@ class PageCacheTest extends TestCase
         }
     }
 
-    public function testCalculateCacheKey()
+    public function testCalculateCacheKey(): void
     {
         $expected = ['yii\filters\PageCache', 'test', 'ru'];
         Yii::$app->requestedRoute = 'test';
@@ -474,7 +474,7 @@ class PageCacheTest extends TestCase
         $this->assertEquals(['yii\filters\PageCache', 'test'], $keys);
     }
 
-    public function testClosureVariations()
+    public function testClosureVariations(): void
     {
         $keys = $this->invokeMethod(new PageCache([
             'variations' => function () {
diff --git a/tests/framework/filters/RateLimiterTest.php b/tests/framework/filters/RateLimiterTest.php
index 47c7e6eead..dd10204d23 100644
--- a/tests/framework/filters/RateLimiterTest.php
+++ b/tests/framework/filters/RateLimiterTest.php
@@ -37,35 +37,35 @@ class RateLimiterTest extends TestCase
         Yii::setLogger(null);
     }
 
-    public function testInitFilledRequest()
+    public function testInitFilledRequest(): void
     {
         $rateLimiter = new RateLimiter(['request' => 'Request']);
 
         $this->assertEquals('Request', $rateLimiter->request);
     }
 
-    public function testInitNotFilledRequest()
+    public function testInitNotFilledRequest(): void
     {
         $rateLimiter = new RateLimiter();
 
         $this->assertInstanceOf(Request::className(), $rateLimiter->request);
     }
 
-    public function testInitFilledResponse()
+    public function testInitFilledResponse(): void
     {
         $rateLimiter = new RateLimiter(['response' => 'Response']);
 
         $this->assertEquals('Response', $rateLimiter->response);
     }
 
-    public function testInitNotFilledResponse()
+    public function testInitNotFilledResponse(): void
     {
         $rateLimiter = new RateLimiter();
 
         $this->assertInstanceOf(Response::className(), $rateLimiter->response);
     }
 
-    public function testBeforeActionUserInstanceOfRateLimitInterface()
+    public function testBeforeActionUserInstanceOfRateLimitInterface(): void
     {
         $rateLimiter = new RateLimiter();
         $rateLimit = new RateLimit();
@@ -79,7 +79,7 @@ class RateLimiterTest extends TestCase
         $this->assertTrue($result);
     }
 
-    public function testBeforeActionUserNotInstanceOfRateLimitInterface()
+    public function testBeforeActionUserNotInstanceOfRateLimitInterface(): void
     {
         $rateLimiter = new RateLimiter(['user' => 'User']);
 
@@ -92,7 +92,7 @@ class RateLimiterTest extends TestCase
         $this->assertTrue($result);
     }
 
-    public function testBeforeActionEmptyUser()
+    public function testBeforeActionEmptyUser(): void
     {
         $user = new User(['identityClass' => RateLimit::className()]);
         Yii::$app->set('user', $user);
@@ -104,7 +104,7 @@ class RateLimiterTest extends TestCase
         $this->assertTrue($result);
     }
 
-    public function testCheckRateLimitTooManyRequests()
+    public function testCheckRateLimitTooManyRequests(): void
     {
         $rateLimit = new RateLimit();
         $rateLimit
@@ -116,7 +116,7 @@ class RateLimiterTest extends TestCase
         $rateLimiter->checkRateLimit($rateLimit, Yii::$app->request, Yii::$app->response, 'testAction');
     }
 
-    public function testCheckRateaddRateLimitHeaders()
+    public function testCheckRateaddRateLimitHeaders(): void
     {
         $rateLimit = new RateLimit();
         $rateLimit
@@ -132,7 +132,7 @@ class RateLimiterTest extends TestCase
         $this->assertEquals(5, $headers->get('X-Rate-Limit-Reset'));
     }
 
-    public function testAddRateLimitHeadersDisabledRateLimitHeaders()
+    public function testAddRateLimitHeadersDisabledRateLimitHeaders(): void
     {
         $rateLimiter = new RateLimiter();
         $rateLimiter->enableRateLimitHeaders = false;
@@ -142,7 +142,7 @@ class RateLimiterTest extends TestCase
         $this->assertCount(0, $response->getHeaders());
     }
 
-    public function testAddRateLimitHeadersEnabledRateLimitHeaders()
+    public function testAddRateLimitHeadersEnabledRateLimitHeaders(): void
     {
         $rateLimiter = new RateLimiter();
         $rateLimiter->enableRateLimitHeaders = true;
@@ -155,7 +155,7 @@ class RateLimiterTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/18236
      */
-    public function testUserWithClosureFunction()
+    public function testUserWithClosureFunction(): void
     {
         $rateLimiter = new RateLimiter();
         $rateLimiter->user = function ($action) {
diff --git a/tests/framework/filters/auth/AuthMethodTest.php b/tests/framework/filters/auth/AuthMethodTest.php
index 7c8e32cf81..8882c31ce4 100644
--- a/tests/framework/filters/auth/AuthMethodTest.php
+++ b/tests/framework/filters/auth/AuthMethodTest.php
@@ -8,6 +8,8 @@
 
 namespace yiiunit\framework\filters\auth;
 
+use stdClass;
+use ReflectionClass;
 use Yii;
 use yii\base\Action;
 use yii\filters\auth\AuthMethod;
@@ -58,12 +60,12 @@ class AuthMethodTest extends TestCase
 
     // Tests :
 
-    public function testBeforeAction()
+    public function testBeforeAction(): void
     {
         $action = $this->createAction();
 
         $filter = $this->createFilter(function () {
-            return new \stdClass();
+            return new stdClass();
         });
         $this->assertTrue($filter->beforeAction($action));
 
@@ -74,9 +76,9 @@ class AuthMethodTest extends TestCase
         $this->assertTrue($filter->beforeAction($action));
     }
 
-    public function testIsOptional()
+    public function testIsOptional(): void
     {
-        $reflection = new \ReflectionClass(AuthMethod::className());
+        $reflection = new ReflectionClass(AuthMethod::className());
         $method = $reflection->getMethod('isOptional');
 
         // @link https://wiki.php.net/rfc/deprecations_php_8_5#deprecate_reflectionsetaccessible
@@ -86,7 +88,7 @@ class AuthMethodTest extends TestCase
         }
 
         $filter = $this->createFilter(function () {
-            return new \stdClass();
+            return new stdClass();
         });
 
         $filter->optional = ['some'];
diff --git a/tests/framework/filters/auth/AuthTest.php b/tests/framework/filters/auth/AuthTest.php
index b5498d87bb..0330bcda7c 100644
--- a/tests/framework/filters/auth/AuthTest.php
+++ b/tests/framework/filters/auth/AuthTest.php
@@ -8,6 +8,8 @@
 
 namespace yiiunit\framework\filters\auth;
 
+use yiiunit\TestCase;
+use ReflectionClass;
 use Yii;
 use yii\base\Action;
 use yii\filters\auth\AuthMethod;
@@ -24,7 +26,7 @@ use yiiunit\framework\filters\stubs\UserIdentity;
  * @author Dmitry Naumenko <d.naumenko.a@gmail.com>
  * @since 2.0.7
  */
-class AuthTest extends \yiiunit\TestCase
+class AuthTest extends TestCase
 {
     protected function setUp(): void
     {
@@ -58,7 +60,7 @@ class AuthTest extends \yiiunit\TestCase
         ];
     }
 
-    public function authOnly($token, $login, $filter)
+    public function authOnly($token, $login, $filter): void
     {
         /** @var TestAuthController $controller */
         $controller = Yii::$app->createController('test-auth')[0];
@@ -69,7 +71,7 @@ class AuthTest extends \yiiunit\TestCase
         }
     }
 
-    public function authOptional($token, $login, $filter)
+    public function authOptional($token, $login, $filter): void
     {
         /** @var TestAuthController $controller */
         $controller = Yii::$app->createController('test-auth')[0];
@@ -80,7 +82,7 @@ class AuthTest extends \yiiunit\TestCase
         }
     }
 
-    public function authExcept($token, $login, $filter)
+    public function authExcept($token, $login, $filter): void
     {
         /** @var TestAuthController $controller */
         $controller = Yii::$app->createController('test-auth')[0];
@@ -91,7 +93,7 @@ class AuthTest extends \yiiunit\TestCase
         }
     }
 
-    public function ensureFilterApplies($token, $login, $filter)
+    public function ensureFilterApplies($token, $login, $filter): void
     {
         $this->authOnly($token, $login, $filter);
         $this->authOptional($token, $login, $filter);
@@ -103,7 +105,7 @@ class AuthTest extends \yiiunit\TestCase
      * @param string|null $token
      * @param string|null $login
      */
-    public function testQueryParamAuth($token, $login)
+    public function testQueryParamAuth($token, $login): void
     {
         $_GET['access-token'] = $token;
         $filter = ['class' => QueryParamAuth::className()];
@@ -115,7 +117,7 @@ class AuthTest extends \yiiunit\TestCase
      * @param string|null $token
      * @param string|null $login
      */
-    public function testHttpHeaderAuth($token, $login)
+    public function testHttpHeaderAuth($token, $login): void
     {
         Yii::$app->request->headers->set('X-Api-Key', $token);
         $filter = ['class' => HttpHeaderAuth::className()];
@@ -127,7 +129,7 @@ class AuthTest extends \yiiunit\TestCase
      * @param string|null $token
      * @param string|null $login
      */
-    public function testHttpBearerAuth($token, $login)
+    public function testHttpBearerAuth($token, $login): void
     {
         Yii::$app->request->headers->set('Authorization', "Bearer $token");
         $filter = ['class' => HttpBearerAuth::className()];
@@ -148,11 +150,11 @@ class AuthTest extends \yiiunit\TestCase
      * @dataProvider authMethodProvider
      * @param string $authClass
      */
-    public function testActive($authClass)
+    public function testActive($authClass): void
     {
         /** @var AuthMethod $filter */
         $filter = new $authClass();
-        $reflection = new \ReflectionClass($filter);
+        $reflection = new ReflectionClass($filter);
         $method = $reflection->getMethod('isActive');
 
         // @link https://wiki.php.net/rfc/deprecations_php_8_5#deprecate_reflectionsetaccessible
@@ -198,7 +200,7 @@ class AuthTest extends \yiiunit\TestCase
         $this->assertFalse($method->invokeArgs($filter, [new Action('view', $controller)]));
     }
 
-    public function testHeaders()
+    public function testHeaders(): void
     {
         Yii::$app->request->headers->set('Authorization', 'Bearer wrong_token');
         $filter = ['class' => HttpBearerAuth::className()];
diff --git a/tests/framework/filters/auth/BasicAuthTest.php b/tests/framework/filters/auth/BasicAuthTest.php
index 7f0967c029..20a51a9c6a 100644
--- a/tests/framework/filters/auth/BasicAuthTest.php
+++ b/tests/framework/filters/auth/BasicAuthTest.php
@@ -26,7 +26,7 @@ class BasicAuthTest extends AuthTest
      * @param string|null $token
      * @param string|null $login
      */
-    public function testHttpBasicAuth($token, $login)
+    public function testHttpBasicAuth($token, $login): void
     {
         $original = $_SERVER;
 
@@ -42,7 +42,7 @@ class BasicAuthTest extends AuthTest
      * @param string|null $token
      * @param string|null $login
      */
-    public function testHttpBasicAuthWithHttpAuthorizationHeader($token, $login)
+    public function testHttpBasicAuthWithHttpAuthorizationHeader($token, $login): void
     {
         $original = $_SERVER;
 
@@ -57,7 +57,7 @@ class BasicAuthTest extends AuthTest
      * @param string|null $token
      * @param string|null $login
      */
-    public function testHttpBasicAuthWithRedirectHttpAuthorizationHeader($token, $login)
+    public function testHttpBasicAuthWithRedirectHttpAuthorizationHeader($token, $login): void
     {
         $original = $_SERVER;
 
@@ -72,7 +72,7 @@ class BasicAuthTest extends AuthTest
      * @param string|null $token
      * @param string|null $login
      */
-    public function testHttpBasicAuthCustom($token, $login)
+    public function testHttpBasicAuthCustom($token, $login): void
     {
         $_SERVER['PHP_AUTH_USER'] = $login;
         $_SERVER['PHP_AUTH_PW'] = 'whatever, we are testers';
@@ -98,7 +98,7 @@ class BasicAuthTest extends AuthTest
      * @param string|null $token
      * @param string|null $login
      */
-    public function testHttpBasicAuthIssue15658($token, $login)
+    public function testHttpBasicAuthIssue15658($token, $login): void
     {
         $_SERVER['PHP_AUTH_USER'] = $login;
         $_SERVER['PHP_AUTH_PW'] = 'y0u7h1nk175r34l?';
@@ -134,7 +134,7 @@ class BasicAuthTest extends AuthTest
      * @param string|null $token
      * @param string|null $login
      */
-    public function testAfterLoginEventIsTriggered18031($token, $login)
+    public function testAfterLoginEventIsTriggered18031($token, $login): void
     {
         $triggered = false;
         Event::on('\yii\web\User', User::EVENT_AFTER_LOGIN, function ($event) use (&$triggered) {
diff --git a/tests/framework/filters/auth/CompositeAuthTest.php b/tests/framework/filters/auth/CompositeAuthTest.php
index ee63ac1493..c3a030fe1d 100644
--- a/tests/framework/filters/auth/CompositeAuthTest.php
+++ b/tests/framework/filters/auth/CompositeAuthTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\filters\auth;
 
+use yiiunit\TestCase;
 use Yii;
 use yii\filters\auth\CompositeAuth;
 use yii\filters\auth\HttpBearerAuth;
@@ -102,7 +103,7 @@ class TestController extends Controller
 /**
  * @group filters
  */
-class CompositeAuthTest extends \yiiunit\TestCase
+class CompositeAuthTest extends TestCase
 {
     protected function setUp(): void
     {
@@ -125,7 +126,7 @@ class CompositeAuthTest extends \yiiunit\TestCase
         $this->mockWebApplication($appConfig);
     }
 
-    public function testCallingRunWithCompleteRoute()
+    public function testCallingRunWithCompleteRoute(): void
     {
         /** @var TestController $controller */
         Yii::$app->request->headers->set('X-Api-Key', 'user1');
@@ -136,7 +137,7 @@ class CompositeAuthTest extends \yiiunit\TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/7409
      */
-    public function testRunAction()
+    public function testRunAction(): void
     {
         /** @var TestController $controller */
         Yii::$app->request->headers->set('X-Api-Key', 'user1');
@@ -144,7 +145,7 @@ class CompositeAuthTest extends \yiiunit\TestCase
         $this->assertEquals('success', $controller->run('b'));
     }
 
-    public function testRunButWithActionIdOnly()
+    public function testRunButWithActionIdOnly(): void
     {
         /** @var TestController $controller */
         Yii::$app->request->headers->set('X-Api-Key', 'user1');
@@ -152,7 +153,7 @@ class CompositeAuthTest extends \yiiunit\TestCase
         $this->assertEquals('success', $controller->run('c'));
     }
 
-    public function testRunWithWrongToken()
+    public function testRunWithWrongToken(): void
     {
         /** @var TestController $controller */
         Yii::$app->request->headers->set('X-Api-Key', 'wrong-user');
@@ -161,7 +162,7 @@ class CompositeAuthTest extends \yiiunit\TestCase
         $controller->run('a');
     }
 
-    public function testRunWithoutAuthHeader()
+    public function testRunWithoutAuthHeader(): void
     {
         /** @var TestController $controller */
         $controller = Yii::$app->createController('test')[0];
@@ -169,7 +170,7 @@ class CompositeAuthTest extends \yiiunit\TestCase
         $controller->run('a');
     }
 
-    public function testRunWithOptionalAction()
+    public function testRunWithOptionalAction(): void
     {
         /** @var TestController $controller */
         $controller = Yii::$app->createController('test')[0];
@@ -253,7 +254,7 @@ class CompositeAuthTest extends \yiiunit\TestCase
      *
      * @dataProvider compositeAuthDataProvider
      */
-    public function testCompositeAuth($authMethods, $actionId, $expectedAuth)
+    public function testCompositeAuth($authMethods, $actionId, $expectedAuth): void
     {
         Yii::$app->request->headers->set('X-Api-Key', 'user1');
         $controller = new TestController('test', Yii::$app, ['authMethods' => $authMethods]);
diff --git a/tests/framework/filters/stubs/ExposedLogger.php b/tests/framework/filters/stubs/ExposedLogger.php
index 5fecfbe2de..a172e1e298 100644
--- a/tests/framework/filters/stubs/ExposedLogger.php
+++ b/tests/framework/filters/stubs/ExposedLogger.php
@@ -12,7 +12,7 @@ use yii\log\Logger;
 
 class ExposedLogger extends Logger
 {
-    public function log($message, $level, $category = 'application')
+    public function log($message, $level, $category = 'application'): void
     {
         $this->messages[] = $message;
     }
diff --git a/tests/framework/grid/ActionColumnTest.php b/tests/framework/grid/ActionColumnTest.php
index a986159b4d..2b653566cf 100644
--- a/tests/framework/grid/ActionColumnTest.php
+++ b/tests/framework/grid/ActionColumnTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\grid;
 
+use yiiunit\TestCase;
 use yii\grid\ActionColumn;
 use yii\helpers\Html;
 
@@ -16,9 +17,9 @@ use yii\helpers\Html;
  *
  * @group grid
  */
-class ActionColumnTest extends \yiiunit\TestCase
+class ActionColumnTest extends TestCase
 {
-    public function testInit()
+    public function testInit(): void
     {
         $column = new ActionColumn();
         $this->assertEquals(['view', 'update', 'delete'], array_keys($column->buttons));
@@ -36,7 +37,7 @@ class ActionColumnTest extends \yiiunit\TestCase
         $this->assertEquals(['view'], array_keys($column->buttons));
     }
 
-    public function testRenderDataCell()
+    public function testRenderDataCell(): void
     {
         $column = new ActionColumn();
         $column->urlCreator = function ($model, $key, $index) {
diff --git a/tests/framework/grid/CheckboxColumnTest.php b/tests/framework/grid/CheckboxColumnTest.php
index 070d08cb9b..a711fbfcb7 100644
--- a/tests/framework/grid/CheckboxColumnTest.php
+++ b/tests/framework/grid/CheckboxColumnTest.php
@@ -33,7 +33,7 @@ class CheckboxColumnTest extends TestCase
         Yii::$app->assetManager->bundles['yii\web\JqueryAsset'] = false;
     }
 
-    public function testInputName()
+    public function testInputName(): void
     {
         $column = new CheckboxColumn(['name' => 'selection', 'grid' => $this->getGrid()]);
         $this->assertStringContainsString('name="selection_all"', $column->renderHeaderCell());
@@ -54,7 +54,7 @@ class CheckboxColumnTest extends TestCase
         $this->assertStringContainsString('name="MyForm[grid1][key_all]"', $column->renderHeaderCell());
     }
 
-    public function testInputValue()
+    public function testInputValue(): void
     {
         $column = new CheckboxColumn(['grid' => $this->getGrid()]);
         $this->assertStringContainsString('value="1"', $column->renderDataCell([], 1, 0));
@@ -85,7 +85,7 @@ class CheckboxColumnTest extends TestCase
         $this->assertStringContainsString('value="42"', $column->renderDataCell([], 1, 0));
     }
 
-    public function testContent()
+    public function testContent(): void
     {
         $column = new CheckboxColumn([
             'content' => function ($model, $key, $index, $column) {
diff --git a/tests/framework/grid/DataColumnTest.php b/tests/framework/grid/DataColumnTest.php
index 5fe977d805..0da1a29be7 100644
--- a/tests/framework/grid/DataColumnTest.php
+++ b/tests/framework/grid/DataColumnTest.php
@@ -8,6 +8,8 @@
 
 namespace yiiunit\framework\grid;
 
+use yiiunit\TestCase;
+use yiiunit\data\base\RulesModel;
 use Yii;
 use yii\data\ActiveDataProvider;
 use yii\data\ArrayDataProvider;
@@ -22,12 +24,12 @@ use yiiunit\data\base\Singer;
  *
  * @group grid
  */
-class DataColumnTest extends \yiiunit\TestCase
+class DataColumnTest extends TestCase
 {
     /**
      * @see DataColumn::getHeaderCellLabel()
      */
-    public function testColumnLabels_OnEmpty_ArrayProvider()
+    public function testColumnLabels_OnEmpty_ArrayProvider(): void
     {
         $this->mockApplication();
         $grid = new GridView([
@@ -48,7 +50,7 @@ class DataColumnTest extends \yiiunit\TestCase
     /**
      * @see DataColumn::getHeaderCellLabel()
      */
-    public function testColumnLabels_OnEmpty_ArrayProvider_WithFilterModel()
+    public function testColumnLabels_OnEmpty_ArrayProvider_WithFilterModel(): void
     {
         $this->mockApplication();
         $grid = new GridView([
@@ -70,7 +72,7 @@ class DataColumnTest extends \yiiunit\TestCase
      * @see DataColumn::$filter
      * @see DataColumn::renderFilterCellContent()
      */
-    public function testFilterInput_String()
+    public function testFilterInput_String(): void
     {
         $this->mockApplication();
         $filterInput = '<input type="text"/>';
@@ -96,7 +98,7 @@ class DataColumnTest extends \yiiunit\TestCase
      * @see DataColumn::$filter
      * @see DataColumn::renderFilterCellContent()
      */
-    public function testFilterHasMaxLengthWhenIsAnActiveTextInput()
+    public function testFilterHasMaxLengthWhenIsAnActiveTextInput(): void
     {
         $this->mockApplication([
             'components' => [
@@ -131,7 +133,7 @@ class DataColumnTest extends \yiiunit\TestCase
      * @see DataColumn::$filter
      * @see DataColumn::renderFilterCellContent()
      */
-    public function testFilterInput_Array()
+    public function testFilterInput_Array(): void
     {
         $this->mockApplication([
             'components' => [
@@ -182,7 +184,7 @@ HTML
      * @see DataColumn::$filter
      * @see DataColumn::renderFilterCellContent()
      */
-    public function testFilterInput_FormatBoolean()
+    public function testFilterInput_FormatBoolean(): void
     {
         $this->mockApplication([
             'components' => [
@@ -232,7 +234,7 @@ HTML
      * @see DataColumn::$filterAttribute
      * @see DataColumn::renderFilterCellContent()
      */
-    public function testFilterInputWithFilterAttribute()
+    public function testFilterInputWithFilterAttribute(): void
     {
         $this->mockApplication();
 
@@ -246,7 +248,7 @@ HTML
                     'filterAttribute' => 'user_id',
                 ],
             ],
-            'filterModel' => new \yiiunit\data\base\RulesModel(['rules' => [['user_id', 'safe']]]),
+            'filterModel' => new RulesModel(['rules' => [['user_id', 'safe']]]),
         ]);
 
         $dataColumn = $grid->columns[0];
diff --git a/tests/framework/grid/GridViewTest.php b/tests/framework/grid/GridViewTest.php
index e9ab08045e..0f08d557b8 100644
--- a/tests/framework/grid/GridViewTest.php
+++ b/tests/framework/grid/GridViewTest.php
@@ -8,6 +8,11 @@
 
 namespace yiiunit\framework\grid;
 
+use yiiunit\TestCase;
+use yii\db\Connection;
+use yii\web\UrlManager;
+use yii\data\ActiveDataProvider;
+use Exception;
 use Yii;
 use yii\data\ArrayDataProvider;
 use yii\grid\DataColumn;
@@ -19,7 +24,7 @@ use yiiunit\data\ar\NoAutoLabels;
  * @author Evgeniy Tkachenko <et.coder@gmail.com>
  * @group grid
  */
-class GridViewTest extends \yiiunit\TestCase
+class GridViewTest extends TestCase
 {
     protected function setUp(): void
     {
@@ -53,9 +58,9 @@ class GridViewTest extends \yiiunit\TestCase
      * @dataProvider emptyDataProvider
      * @param mixed $emptyText
      * @param string $expectedText
-     * @throws \Exception
+     * @throws Exception
      */
-    public function testEmpty($emptyText, $expectedText)
+    public function testEmpty($emptyText, $expectedText): void
     {
         $html = GridView::widget([
             'id' => 'grid',
@@ -79,7 +84,7 @@ class GridViewTest extends \yiiunit\TestCase
         $this->assertEquals($expectedHtml, $html);
     }
 
-    public function testGuessColumns()
+    public function testGuessColumns(): void
     {
         $row = ['id' => 1, 'name' => 'Name1', 'value' => 'Value1', 'description' => 'Description1'];
 
@@ -126,9 +131,9 @@ class GridViewTest extends \yiiunit\TestCase
     }
 
     /**
-     * @throws \Exception
+     * @throws Exception
      */
-    public function testFooter()
+    public function testFooter(): void
     {
         $config = [
             'id'           => 'grid',
@@ -155,13 +160,13 @@ class GridViewTest extends \yiiunit\TestCase
         $this->assertTrue(preg_match('/<\/tbody><tfoot>/', $html) === 1);
     }
 
-    public function testHeaderLabels()
+    public function testHeaderLabels(): void
     {
         // Ensure GridView does not call Model::generateAttributeLabel() to generate labels unless the labels are explicitly used.
         $this->mockApplication([
             'components' => [
                 'db' => [
-                    'class' => \yii\db\Connection::className(),
+                    'class' => Connection::className(),
                     'dsn' => 'sqlite::memory:',
                 ],
             ],
@@ -170,13 +175,13 @@ class GridViewTest extends \yiiunit\TestCase
         NoAutoLabels::$db = Yii::$app->getDb();
         Yii::$app->getDb()->createCommand()->createTable(NoAutoLabels::tableName(), ['attr1' => 'int', 'attr2' => 'int'])->execute();
 
-        $urlManager = new \yii\web\UrlManager([
+        $urlManager = new UrlManager([
             'baseUrl' => '/',
             'scriptUrl' => '/index.php',
         ]);
 
         $grid = new GridView([
-            'dataProvider' => new \yii\data\ActiveDataProvider([
+            'dataProvider' => new ActiveDataProvider([
                 'query' => NoAutoLabels::find(),
             ]),
             'columns' => [
diff --git a/tests/framework/grid/RadiobuttonColumnTest.php b/tests/framework/grid/RadiobuttonColumnTest.php
index 958a441450..4de1bd4ecc 100644
--- a/tests/framework/grid/RadiobuttonColumnTest.php
+++ b/tests/framework/grid/RadiobuttonColumnTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\grid;
 
+use yii\base\InvalidConfigException;
 use Yii;
 use yii\data\ArrayDataProvider;
 use yii\grid\GridView;
@@ -23,9 +24,9 @@ use yiiunit\TestCase;
  */
 class RadiobuttonColumnTest extends TestCase
 {
-    public function testException()
+    public function testException(): void
     {
-        $this->expectException(\yii\base\InvalidConfigException::class);
+        $this->expectException(InvalidConfigException::class);
         $this->expectExceptionMessage('The "name" property must be set.');
 
         new RadioButtonColumn([
@@ -33,7 +34,7 @@ class RadiobuttonColumnTest extends TestCase
         ]);
     }
 
-    public function testOptionsByArray()
+    public function testOptionsByArray(): void
     {
         $column = new RadioButtonColumn([
             'radioOptions' => [
@@ -43,7 +44,7 @@ class RadiobuttonColumnTest extends TestCase
         $this->assertEquals('<td><input type="radio" name="radioButtonSelection" value="42"></td>', $column->renderDataCell([], 1, 0));
     }
 
-    public function testOptionsByCallback()
+    public function testOptionsByCallback(): void
     {
         $model = [
             'label' => 'label',
@@ -60,7 +61,7 @@ class RadiobuttonColumnTest extends TestCase
         $this->assertEquals('<td><input type="radio" name="radioButtonSelection" value="' . $model['value'] . '"></td>', $actual);
     }
 
-    public function testContent()
+    public function testContent(): void
     {
         $column = new RadioButtonColumn([
             'content' => function ($model, $key, $index, $column) {
@@ -77,7 +78,7 @@ class RadiobuttonColumnTest extends TestCase
         $this->assertStringContainsString(Html::radio('radioButtonInput', false), $column->renderDataCell([], 1, 0));
     }
 
-    public function testMultipleInGrid()
+    public function testMultipleInGrid(): void
     {
         $this->mockApplication();
         Yii::setAlias('@webroot', '@yiiunit/runtime');
diff --git a/tests/framework/helpers/ArrayHelperTest.php b/tests/framework/helpers/ArrayHelperTest.php
index eb89c1d98c..68e2b33fa9 100644
--- a/tests/framework/helpers/ArrayHelperTest.php
+++ b/tests/framework/helpers/ArrayHelperTest.php
@@ -8,6 +8,14 @@
 
 namespace yiiunit\framework\helpers;
 
+use DateTime;
+use DateTimeZone;
+use stdClass;
+use yii\helpers\UnsetArrayValue;
+use yii\helpers\ReplaceArrayValue;
+use ArrayObject;
+use Throwable;
+use ReturnTypeWillChange;
 use ArrayAccess;
 use Iterator;
 use yii\base\BaseObject;
@@ -29,7 +37,7 @@ class ArrayHelperTest extends TestCase
         $this->destroyApplication();
     }
 
-    public function testToArray()
+    public function testToArray(): void
     {
         $dataArrayable = $this->getMockBuilder('yii\\base\\Arrayable')->getMock();
         $dataArrayable->method('toArray')->willReturn([]);
@@ -121,10 +129,10 @@ class ArrayHelperTest extends TestCase
             'date' => '2021-09-13 15:16:17.000000',
             'timezone_type' => 3,
             'timezone' => 'UTC',
-        ], ArrayHelper::toArray(new \DateTime('2021-09-13 15:16:17', new \DateTimeZone('UTC'))));
+        ], ArrayHelper::toArray(new DateTime('2021-09-13 15:16:17', new DateTimeZone('UTC'))));
     }
 
-    public function testRemove()
+    public function testRemove(): void
     {
         $array = ['name' => 'b', 'age' => 3];
         $name = ArrayHelper::remove($array, 'name');
@@ -139,7 +147,7 @@ class ArrayHelperTest extends TestCase
     /**
      * @return void
      */
-    public function testRemoveWithFloat()
+    public function testRemoveWithFloat(): void
     {
         if (version_compare(PHP_VERSION, '8.1.0', '>=')) {
             $this->markTestSkipped('Using floats as array key is deprecated.');
@@ -159,7 +167,7 @@ class ArrayHelperTest extends TestCase
         $this->assertEquals('defaultValue', $default);
     }
 
-    public function testRemoveValueMultiple()
+    public function testRemoveValueMultiple(): void
     {
         $array = [
             'Bob' => 'Dylan',
@@ -180,7 +188,7 @@ class ArrayHelperTest extends TestCase
         ], $removed);
     }
 
-    public function testRemoveValueNotExisting()
+    public function testRemoveValueNotExisting(): void
     {
         $array = [
             'Bob' => 'Dylan',
@@ -200,7 +208,7 @@ class ArrayHelperTest extends TestCase
         $this->assertEquals([], $removed);
     }
 
-    public function testMultisort()
+    public function testMultisort(): void
     {
         // empty key
         $dataEmpty = [];
@@ -250,17 +258,17 @@ class ArrayHelperTest extends TestCase
         $this->assertEquals(['name' => 'B', 'age' => 4], $array[3]);
     }
 
-    public function testMultisortNestedObjects()
+    public function testMultisortNestedObjects(): void
     {
-        $obj1 = new \stdClass();
+        $obj1 = new stdClass();
         $obj1->type = 'def';
         $obj1->owner = $obj1;
 
-        $obj2 = new \stdClass();
+        $obj2 = new stdClass();
         $obj2->type = 'abc';
         $obj2->owner = $obj2;
 
-        $obj3 = new \stdClass();
+        $obj3 = new stdClass();
         $obj3->type = 'abc';
         $obj3->owner = $obj3;
 
@@ -283,7 +291,7 @@ class ArrayHelperTest extends TestCase
         $this->assertEquals($obj3, $models[2]);
     }
 
-    public function testMultisortUseSort()
+    public function testMultisortUseSort(): void
     {
         // single key
         $sort = new Sort([
@@ -322,7 +330,7 @@ class ArrayHelperTest extends TestCase
         $this->assertEquals(['name' => 'b', 'age' => 3], $array[2]);
     }
 
-    public function testMultisortClosure()
+    public function testMultisortClosure(): void
     {
         $changelog = [
             '- Enh #123: test1',
@@ -349,21 +357,21 @@ class ArrayHelperTest extends TestCase
         ], $changelog);
     }
 
-    public function testMultisortInvalidParamExceptionDirection()
+    public function testMultisortInvalidParamExceptionDirection(): void
     {
         $this->expectException('yii\base\InvalidParamException');
         $data = ['foo' => 'bar'];
         ArrayHelper::multisort($data, ['foo'], []);
     }
 
-    public function testMultisortInvalidParamExceptionSortFlag()
+    public function testMultisortInvalidParamExceptionSortFlag(): void
     {
         $this->expectException('yii\base\InvalidParamException');
         $data = ['foo' => 'bar'];
         ArrayHelper::multisort($data, ['foo'], ['foo'], []);
     }
 
-    public function testMerge()
+    public function testMerge(): void
     {
         $a = [
             'name' => 'Yii',
@@ -415,7 +423,7 @@ class ArrayHelperTest extends TestCase
         $this->assertEquals($expected, $result);
     }
 
-    public function testMergeWithNumericKeys()
+    public function testMergeWithNumericKeys(): void
     {
         $a = [10 => [1]];
         $b = [10 => [2]];
@@ -426,7 +434,7 @@ class ArrayHelperTest extends TestCase
         $this->assertEquals($expected, $result);
     }
 
-    public function testMergeWithUnset()
+    public function testMergeWithUnset(): void
     {
         $a = [
             'name' => 'Yii',
@@ -441,7 +449,7 @@ class ArrayHelperTest extends TestCase
         ];
         $b = [
             'version' => '1.1',
-            'options' => new \yii\helpers\UnsetArrayValue(),
+            'options' => new UnsetArrayValue(),
             'features' => [
                 'gii',
             ],
@@ -460,7 +468,7 @@ class ArrayHelperTest extends TestCase
         $this->assertEquals($expected, $result);
     }
 
-    public function testMergeWithReplace()
+    public function testMergeWithReplace(): void
     {
         $a = [
             'name' => 'Yii',
@@ -478,7 +486,7 @@ class ArrayHelperTest extends TestCase
             'options' => [
                 'unittest' => true,
             ],
-            'features' => new \yii\helpers\ReplaceArrayValue([
+            'features' => new ReplaceArrayValue([
                 'gii',
             ]),
         ];
@@ -499,7 +507,7 @@ class ArrayHelperTest extends TestCase
         $this->assertEquals($expected, $result);
     }
 
-    public function testMergeWithNullValues()
+    public function testMergeWithNullValues(): void
     {
         $a = [
             'firstValue',
@@ -521,7 +529,7 @@ class ArrayHelperTest extends TestCase
         $this->assertEquals($expected, $result);
     }
 
-    public function testMergeEmpty()
+    public function testMergeEmpty(): void
     {
         $this->assertEquals([], ArrayHelper::merge([], []));
         $this->assertEquals([], ArrayHelper::merge([], [], []));
@@ -530,7 +538,7 @@ class ArrayHelperTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/pull/11549
      */
-    public function testGetValueWithFloatKeys()
+    public function testGetValueWithFloatKeys(): void
     {
         if (version_compare(PHP_VERSION, '8.1.0', '>=')) {
             $this->markTestSkipped('Using floats as array key is deprecated.');
@@ -547,7 +555,7 @@ class ArrayHelperTest extends TestCase
         $this->assertNull($result);
     }
 
-    public function testIndex()
+    public function testIndex(): void
     {
         $array = [
             ['id' => '123', 'data' => 'abc'],
@@ -585,7 +593,7 @@ class ArrayHelperTest extends TestCase
         ], $result);
     }
 
-    public function testIndexGroupBy()
+    public function testIndexGroupBy(): void
     {
         $array = [
             ['id' => '123', 'data' => 'abc'],
@@ -668,7 +676,7 @@ class ArrayHelperTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/11739
      */
-    public function testIndexFloat()
+    public function testIndexFloat(): void
     {
         $array = [
             ['id' => 1e6],
@@ -689,7 +697,7 @@ class ArrayHelperTest extends TestCase
         $this->assertEquals($expected, $result);
     }
 
-    public function testGetColumn()
+    public function testGetColumn(): void
     {
         $array = [
             'a' => ['id' => '123', 'data' => 'abc'],
@@ -710,7 +718,7 @@ class ArrayHelperTest extends TestCase
         $this->assertEquals(['abc', 'def'], $result);
     }
 
-    public function testMap()
+    public function testMap(): void
     {
         $array = [
             ['id' => '123', 'name' => 'aaa', 'class' => 'x'],
@@ -790,7 +798,7 @@ class ArrayHelperTest extends TestCase
         ], $result);
     }
 
-    public function testKeyExists()
+    public function testKeyExists(): void
     {
         $array = [
             'a' => 1,
@@ -808,7 +816,7 @@ class ArrayHelperTest extends TestCase
         $this->assertFalse(ArrayHelper::keyExists('c', $array, false));
     }
 
-    public function testKeyExistsWithFloat()
+    public function testKeyExistsWithFloat(): void
     {
         if (version_compare(PHP_VERSION, '8.1.0', '>=')) {
             $this->markTestSkipped('Using floats as array key is deprecated.');
@@ -829,7 +837,7 @@ class ArrayHelperTest extends TestCase
         $this->assertTrue(ArrayHelper::keyExists(3.3, $array));
     }
 
-    public function testKeyExistsArrayAccess()
+    public function testKeyExistsArrayAccess(): void
     {
         $array = new TraversableArrayAccessibleObject([
             'a' => 1,
@@ -842,7 +850,7 @@ class ArrayHelperTest extends TestCase
         $this->assertFalse(ArrayHelper::keyExists('c', $array));
     }
 
-    public function testKeyExistsArrayAccessCaseInsensitiveThrowsError()
+    public function testKeyExistsArrayAccessCaseInsensitiveThrowsError(): void
     {
         $this->expectException('yii\base\InvalidArgumentException');
         $this->expectExceptionMessage('Second parameter($array) cannot be ArrayAccess in case insensitive mode');
@@ -890,7 +898,7 @@ class ArrayHelperTest extends TestCase
      * @param $expected
      * @param null $default
      */
-    public function testGetValue($key, $expected, $default = null)
+    public function testGetValue($key, $expected, $default = null): void
     {
         $array = [
             'name' => 'test',
@@ -919,32 +927,32 @@ class ArrayHelperTest extends TestCase
         $this->assertEquals($expected, ArrayHelper::getValue($array, $key, $default));
     }
 
-    public function testGetValueObjects()
+    public function testGetValueObjects(): void
     {
-        $arrayObject = new \ArrayObject(['id' => 23], \ArrayObject::ARRAY_AS_PROPS);
+        $arrayObject = new ArrayObject(['id' => 23], ArrayObject::ARRAY_AS_PROPS);
         $this->assertEquals(23, ArrayHelper::getValue($arrayObject, 'id'));
 
         $object = new Post1();
         $this->assertEquals(23, ArrayHelper::getValue($object, 'id'));
     }
 
-    public function testGetValueNonexistingProperties1()
+    public function testGetValueNonexistingProperties1(): void
     {
         try {
             $object = new Post1();
             ArrayHelper::getValue($object, 'nonExisting');
-        } catch (\Throwable $th) {
+        } catch (Throwable $th) {
             $this->assertEquals('Undefined property: yiiunit\framework\helpers\Post1::$nonExisting', $th->getMessage());
         }
     }
 
-    public function testGetValueNonexistingPropertiesForArrayObject()
+    public function testGetValueNonexistingPropertiesForArrayObject(): void
     {
-        $arrayObject = new \ArrayObject(['id' => 23], \ArrayObject::ARRAY_AS_PROPS);
+        $arrayObject = new ArrayObject(['id' => 23], ArrayObject::ARRAY_AS_PROPS);
         $this->assertNull(ArrayHelper::getValue($arrayObject, 'nonExisting'));
     }
 
-    public function testGetValueFromArrayAccess()
+    public function testGetValueFromArrayAccess(): void
     {
         $arrayAccessibleObject = new ArrayAccessibleObject([
             'one'   => 1,
@@ -957,7 +965,7 @@ class ArrayHelperTest extends TestCase
         $this->assertEquals(1, ArrayHelper::getValue($arrayAccessibleObject, 'one'));
     }
 
-    public function testGetValueWithDotsFromArrayAccess()
+    public function testGetValueWithDotsFromArrayAccess(): void
     {
         $arrayAccessibleObject = new ArrayAccessibleObject([
             'one'   => 1,
@@ -970,7 +978,7 @@ class ArrayHelperTest extends TestCase
         $this->assertEquals('dot', ArrayHelper::getValue($arrayAccessibleObject, 'key.with.dot'));
     }
 
-    public function testGetValueNonexistingArrayAccess()
+    public function testGetValueNonexistingArrayAccess(): void
     {
         $arrayAccessibleObject = new ArrayAccessibleObject([
             'one'   => 1,
@@ -1217,13 +1225,13 @@ class ArrayHelperTest extends TestCase
      * @param mixed $value
      * @param mixed $expected
      */
-    public function testSetValue($array_input, $key, $value, $expected)
+    public function testSetValue($array_input, $key, $value, $expected): void
     {
         ArrayHelper::setValue($array_input, $key, $value);
         $this->assertEquals($expected, $array_input);
     }
 
-    public function testIsAssociative()
+    public function testIsAssociative(): void
     {
         $this->assertFalse(ArrayHelper::isAssociative('test'));
         $this->assertFalse(ArrayHelper::isAssociative([]));
@@ -1234,7 +1242,7 @@ class ArrayHelperTest extends TestCase
         $this->assertTrue(ArrayHelper::isAssociative(['name' => 1, 'value' => 'test', 3], false));
     }
 
-    public function testIsIndexed()
+    public function testIsIndexed(): void
     {
         $this->assertFalse(ArrayHelper::isIndexed('test'));
         $this->assertTrue(ArrayHelper::isIndexed([]));
@@ -1244,7 +1252,7 @@ class ArrayHelperTest extends TestCase
         $this->assertFalse(ArrayHelper::isIndexed(['a' => 'b'], false));
     }
 
-    public function testHtmlEncode()
+    public function testHtmlEncode(): void
     {
         $array = [
             'abc' => '123',
@@ -1281,7 +1289,7 @@ class ArrayHelperTest extends TestCase
         ], ArrayHelper::htmlEncode($array, false));
     }
 
-    public function testHtmlDecode()
+    public function testHtmlDecode(): void
     {
         $array = [
             'abc' => '123',
@@ -1321,70 +1329,70 @@ class ArrayHelperTest extends TestCase
         $this->assertEquals($expected, ArrayHelper::htmlDecode($array, false));
     }
 
-    public function testIsIn()
+    public function testIsIn(): void
     {
-        $this->assertTrue(ArrayHelper::isIn('a', new \ArrayObject(['a', 'b'])));
+        $this->assertTrue(ArrayHelper::isIn('a', new ArrayObject(['a', 'b'])));
         $this->assertTrue(ArrayHelper::isIn('a', ['a', 'b']));
 
-        $this->assertTrue(ArrayHelper::isIn('1', new \ArrayObject([1, 'b'])));
+        $this->assertTrue(ArrayHelper::isIn('1', new ArrayObject([1, 'b'])));
         $this->assertTrue(ArrayHelper::isIn('1', [1, 'b']));
 
-        $this->assertFalse(ArrayHelper::isIn('1', new \ArrayObject([1, 'b']), true));
+        $this->assertFalse(ArrayHelper::isIn('1', new ArrayObject([1, 'b']), true));
         $this->assertFalse(ArrayHelper::isIn('1', [1, 'b'], true));
 
-        $this->assertTrue(ArrayHelper::isIn(['a'], new \ArrayObject([['a'], 'b'])));
-        $this->assertFalse(ArrayHelper::isIn('a', new \ArrayObject([['a'], 'b'])));
+        $this->assertTrue(ArrayHelper::isIn(['a'], new ArrayObject([['a'], 'b'])));
+        $this->assertFalse(ArrayHelper::isIn('a', new ArrayObject([['a'], 'b'])));
         $this->assertFalse(ArrayHelper::isIn('a', [['a'], 'b']));
     }
 
-    public function testIsInStrict()
+    public function testIsInStrict(): void
     {
         // strict comparison
-        $this->assertTrue(ArrayHelper::isIn(1, new \ArrayObject([1, 'a']), true));
+        $this->assertTrue(ArrayHelper::isIn(1, new ArrayObject([1, 'a']), true));
         $this->assertTrue(ArrayHelper::isIn(1, [1, 'a'], true));
 
-        $this->assertFalse(ArrayHelper::isIn('1', new \ArrayObject([1, 'a']), true));
+        $this->assertFalse(ArrayHelper::isIn('1', new ArrayObject([1, 'a']), true));
         $this->assertFalse(ArrayHelper::isIn('1', [1, 'a'], true));
     }
 
-    public function testInException()
+    public function testInException(): void
     {
         $this->expectException('yii\base\InvalidParamException');
         $this->expectExceptionMessage('Argument $haystack must be an array or implement Traversable');
         ArrayHelper::isIn('value', null);
     }
 
-    public function testIsSubset()
+    public function testIsSubset(): void
     {
-        $this->assertTrue(ArrayHelper::isSubset(['a'], new \ArrayObject(['a', 'b'])));
-        $this->assertTrue(ArrayHelper::isSubset(new \ArrayObject(['a']), ['a', 'b']));
+        $this->assertTrue(ArrayHelper::isSubset(['a'], new ArrayObject(['a', 'b'])));
+        $this->assertTrue(ArrayHelper::isSubset(new ArrayObject(['a']), ['a', 'b']));
 
-        $this->assertTrue(ArrayHelper::isSubset([1], new \ArrayObject(['1', 'b'])));
-        $this->assertTrue(ArrayHelper::isSubset(new \ArrayObject([1]), ['1', 'b']));
+        $this->assertTrue(ArrayHelper::isSubset([1], new ArrayObject(['1', 'b'])));
+        $this->assertTrue(ArrayHelper::isSubset(new ArrayObject([1]), ['1', 'b']));
 
-        $this->assertFalse(ArrayHelper::isSubset([1], new \ArrayObject(['1', 'b']), true));
-        $this->assertFalse(ArrayHelper::isSubset(new \ArrayObject([1]), ['1', 'b'], true));
+        $this->assertFalse(ArrayHelper::isSubset([1], new ArrayObject(['1', 'b']), true));
+        $this->assertFalse(ArrayHelper::isSubset(new ArrayObject([1]), ['1', 'b'], true));
     }
 
-    public function testIsSubsetException()
+    public function testIsSubsetException(): void
     {
         $this->expectException('yii\base\InvalidParamException');
         $this->expectExceptionMessage('Argument $needles must be an array or implement Traversable');
-        ArrayHelper::isSubset('a', new \ArrayObject(['a', 'b']));
+        ArrayHelper::isSubset('a', new ArrayObject(['a', 'b']));
     }
 
-    public function testIsArray()
+    public function testIsArray(): void
     {
         $this->assertTrue(ArrayHelper::isTraversable(['a']));
-        $this->assertTrue(ArrayHelper::isTraversable(new \ArrayObject(['1'])));
-        $this->assertFalse(ArrayHelper::isTraversable(new \stdClass()));
+        $this->assertTrue(ArrayHelper::isTraversable(new ArrayObject(['1'])));
+        $this->assertFalse(ArrayHelper::isTraversable(new stdClass()));
         $this->assertFalse(ArrayHelper::isTraversable('A,B,C'));
         $this->assertFalse(ArrayHelper::isTraversable(12));
         $this->assertFalse(ArrayHelper::isTraversable(false));
         $this->assertFalse(ArrayHelper::isTraversable(null));
     }
 
-    public function testFilter()
+    public function testFilter(): void
     {
         $array = [
             'A' => [
@@ -1508,7 +1516,7 @@ class ArrayHelperTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/18395
      */
-    public function testFilterForIntegerKeys()
+    public function testFilterForIntegerKeys(): void
     {
         $array = ['a', 'b', ['c', 'd']];
 
@@ -1518,18 +1526,18 @@ class ArrayHelperTest extends TestCase
         $this->assertEquals([2 => [1 => 'd']], ArrayHelper::filter($array, [2, '!2.0']));
     }
 
-    public function testFilterWithInvalidValues()
+    public function testFilterWithInvalidValues(): void
     {
         $array = ['a' => 'b'];
 
-        $this->assertEquals([], ArrayHelper::filter($array, [new \stdClass()]));
+        $this->assertEquals([], ArrayHelper::filter($array, [new stdClass()]));
         $this->assertEquals([], ArrayHelper::filter($array, [['a']]));
     }
 
     /**
      * @see https://github.com/yiisoft/yii2/issues/18086
      */
-    public function testArrayAccessWithPublicProperty()
+    public function testArrayAccessWithPublicProperty(): void
     {
         $data = new ArrayAccessibleObject(['value' => 123]);
 
@@ -1541,7 +1549,7 @@ class ArrayHelperTest extends TestCase
      * https://github.com/yiisoft/yii2/commit/35fb9c624893855317e5fe52e6a21f6518a9a31c changed the way
      * ArrayHelper works with existing object properties in case of ArrayAccess.
      */
-    public function testArrayAccessWithMagicProperty()
+    public function testArrayAccessWithMagicProperty(): void
     {
         $model = new MagicModel();
         $this->assertEquals(42, ArrayHelper::getValue($model, 'magic'));
@@ -1553,7 +1561,7 @@ class ArrayHelperTest extends TestCase
      *
      * @return void
      */
-    public function testRecursiveSort($expected_result, $input_array)
+    public function testRecursiveSort($expected_result, $input_array): void
     {
         $actual = ArrayHelper::recursiveSort($input_array);
         $this->assertEquals($expected_result, $actual);
@@ -1614,7 +1622,7 @@ class ArrayHelperTest extends TestCase
         ];
     }
 
-    public function testFlatten()
+    public function testFlatten(): void
     {
         // Test with deeply nested arrays
         $array = [
@@ -1703,7 +1711,7 @@ class ArrayHelperTest extends TestCase
         $this->assertEquals($expected, $result);
     }
 
-    public function testFlattenEdgeCases()
+    public function testFlattenEdgeCases(): void
     {
         // Empty array
         $array = [];
@@ -1758,7 +1766,7 @@ class Post3 extends BaseObject
     /** @var BaseObject */
     public $subObject;
 
-    public function init()
+    public function init(): void
     {
         $this->subObject = new Post2();
     }
@@ -1774,8 +1782,8 @@ class ArrayAccessibleObject implements ArrayAccess
         $this->container = $container;
     }
 
-    #[\ReturnTypeWillChange]
-    public function offsetSet($offset, $value)
+    #[ReturnTypeWillChange]
+    public function offsetSet($offset, $value): void
     {
         if (is_null($offset)) {
             $this->container[] = $value;
@@ -1784,19 +1792,19 @@ class ArrayAccessibleObject implements ArrayAccess
         }
     }
 
-    #[\ReturnTypeWillChange]
+    #[ReturnTypeWillChange]
     public function offsetExists($offset)
     {
         return array_key_exists($offset, $this->container);
     }
 
-    #[\ReturnTypeWillChange]
-    public function offsetUnset($offset)
+    #[ReturnTypeWillChange]
+    public function offsetUnset($offset): void
     {
         unset($this->container[$offset]);
     }
 
-    #[\ReturnTypeWillChange]
+    #[ReturnTypeWillChange]
     public function offsetGet($offset)
     {
         return $this->offsetExists($offset) ? $this->container[$offset] : null;
@@ -1820,31 +1828,31 @@ class TraversableArrayAccessibleObject extends ArrayAccessibleObject implements
         return array_key_exists($keyIndex, $keys) ? $keys[$keyIndex] : false;
     }
 
-    #[\ReturnTypeWillChange]
-    public function rewind()
+    #[ReturnTypeWillChange]
+    public function rewind(): void
     {
         $this->position = 0;
     }
 
-    #[\ReturnTypeWillChange]
+    #[ReturnTypeWillChange]
     public function current()
     {
         return $this->offsetGet($this->getContainerKey($this->position));
     }
 
-    #[\ReturnTypeWillChange]
+    #[ReturnTypeWillChange]
     public function key()
     {
         return $this->getContainerKey($this->position);
     }
 
-    #[\ReturnTypeWillChange]
-    public function next()
+    #[ReturnTypeWillChange]
+    public function next(): void
     {
         ++$this->position;
     }
 
-    #[\ReturnTypeWillChange]
+    #[ReturnTypeWillChange]
     public function valid()
     {
         $key = $this->getContainerKey($this->position);
diff --git a/tests/framework/helpers/BaseConsoleTest.php b/tests/framework/helpers/BaseConsoleTest.php
index d6e432ad79..8ccaee812a 100644
--- a/tests/framework/helpers/BaseConsoleTest.php
+++ b/tests/framework/helpers/BaseConsoleTest.php
@@ -22,7 +22,7 @@ class BaseConsoleTest extends TestCase
     /**
      * @test
      */
-    public function renderColoredString()
+    public function renderColoredString(): void
     {
         $data = '%yfoo';
         $actual = BaseConsole::renderColoredString($data);
@@ -37,7 +37,7 @@ class BaseConsoleTest extends TestCase
     /**
      * @test
      */
-    public function ansiColorizedSubstr_withoutColors()
+    public function ansiColorizedSubstr_withoutColors(): void
     {
         $str = 'FooBar';
 
@@ -62,7 +62,7 @@ class BaseConsoleTest extends TestCase
      * @param $length
      * @param $expected
      */
-    public function ansiColorizedSubstr_withColors($str, $start, $length, $expected)
+    public function ansiColorizedSubstr_withColors($str, $start, $length, $expected): void
     {
         $ansiStr = BaseConsole::renderColoredString($str);
 
@@ -82,7 +82,7 @@ class BaseConsoleTest extends TestCase
         ];
     }
 
-    public function testAnsiStrlen()
+    public function testAnsiStrlen(): void
     {
         $this->assertSame(3, BaseConsole::ansiStrlen('Foo'));
         $this->assertSame(3, BaseConsole::ansiStrlen(BaseConsole::renderColoredString('Bar%y')));
diff --git a/tests/framework/helpers/BaseUrlTest.php b/tests/framework/helpers/BaseUrlTest.php
index 9bcd39ef98..28d1ca7358 100644
--- a/tests/framework/helpers/BaseUrlTest.php
+++ b/tests/framework/helpers/BaseUrlTest.php
@@ -11,19 +11,19 @@ use yii\helpers\BaseUrl;
 class BaseUrlTest extends TestCase
 {
     /** @dataProvider relativeTrueUrlProvider */
-    public function testIsRelativeWillReturnTrue($url)
+    public function testIsRelativeWillReturnTrue($url): void
     {
         $this->assertTrue(BaseUrl::isRelative($url));
     }
 
     /** @dataProvider relativeFalseUrlProvider */
-    public function testIsRelativeWillReturnFalse($url)
+    public function testIsRelativeWillReturnFalse($url): void
     {
         $this->assertFalse(BaseUrl::isRelative($url));
     }
 
     /** @dataProvider ensureSchemeUrlProvider */
-    public function testEnsureScheme($url, $scheme, $expected)
+    public function testEnsureScheme($url, $scheme, $expected): void
     {
         $this->assertEquals($expected, BaseUrl::ensureScheme($url, $scheme));
     }
diff --git a/tests/framework/helpers/ConsoleTest.php b/tests/framework/helpers/ConsoleTest.php
index 9e6f956fdf..51698ab405 100644
--- a/tests/framework/helpers/ConsoleTest.php
+++ b/tests/framework/helpers/ConsoleTest.php
@@ -86,7 +86,7 @@ class ConsoleTest extends TestCase
         rewind(ConsoleStub::$inputStream);
     }
 
-    public function testStripAnsiFormat()
+    public function testStripAnsiFormat(): void
     {
         ob_start();
         ob_implicit_flush(false);
@@ -201,12 +201,12 @@ class ConsoleTest extends TestCase
      * @param string $ansi
      * @param string $html
      */
-    public function testAnsi2Html($ansi, $html)
+    public function testAnsi2Html($ansi, $html): void
     {
         $this->assertEquals($html, Console::ansiToHtml($ansi));
     }
 
-    public function testErrorSummary()
+    public function testErrorSummary(): void
     {
         $model = new TestConsoleModel();
         $model->name = 'not_an_integer';
@@ -221,7 +221,7 @@ class ConsoleTest extends TestCase
     /**
      * @covers \yii\helpers\BaseConsole::input()
      */
-    public function testInput()
+    public function testInput(): void
     {
         $this->sendInput('test1');
         $result = ConsoleStub::input();
@@ -239,7 +239,7 @@ class ConsoleTest extends TestCase
     /**
      * @covers \yii\helpers\BaseConsole::output()
      */
-    public function testOutput()
+    public function testOutput(): void
     {
         $result = ConsoleStub::output('Smth');
         $this->assertEquals('Smth' . PHP_EOL, $this->readOutput());
@@ -249,7 +249,7 @@ class ConsoleTest extends TestCase
     /**
      * @covers \yii\helpers\BaseConsole::error()
      */
-    public function testError()
+    public function testError(): void
     {
         $result = ConsoleStub::error('SomeError');
         $this->assertEquals('SomeError' . PHP_EOL, $this->readOutput(ConsoleStub::$errorStream));
@@ -259,7 +259,7 @@ class ConsoleTest extends TestCase
     /**
      * @covers \yii\helpers\BaseConsole::prompt()
      */
-    public function testPrompt()
+    public function testPrompt(): void
     {
         // testing output variations
 
@@ -350,7 +350,7 @@ class ConsoleTest extends TestCase
     /**
      * @covers \yii\helpers\BaseConsole::confirm()
      */
-    public function testConfirm()
+    public function testConfirm(): void
     {
         $this->sendInput('y');
         ConsoleStub::confirm('Are you sure?');
@@ -392,7 +392,7 @@ class ConsoleTest extends TestCase
     /**
      * @covers \yii\helpers\BaseConsole::select()
      */
-    public function testSelect()
+    public function testSelect(): void
     {
         $options = [
             'c' => 'cat',
@@ -457,7 +457,7 @@ class TestConsoleModel extends DynamicModel
         ];
     }
 
-    public function init()
+    public function init(): void
     {
         $this->defineAttribute('name');
     }
diff --git a/tests/framework/helpers/FileHelperTest.php b/tests/framework/helpers/FileHelperTest.php
index 88f01bba4b..7df3c08d05 100644
--- a/tests/framework/helpers/FileHelperTest.php
+++ b/tests/framework/helpers/FileHelperTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\helpers;
 
+use Exception;
 use stdClass;
 use Yii;
 use yii\helpers\FileHelper;
@@ -150,7 +151,7 @@ class FileHelperTest extends TestCase
 
     // Tests :
 
-    public function testCreateDirectory()
+    public function testCreateDirectory(): void
     {
         $basePath = $this->testFilePath;
         $dirName = $basePath . DIRECTORY_SEPARATOR . 'test_dir_level_1' . DIRECTORY_SEPARATOR . 'test_dir_level_2';
@@ -166,7 +167,7 @@ class FileHelperTest extends TestCase
     /**
      * @depends testCreateDirectory
      */
-    public function testCopyDirectory()
+    public function testCopyDirectory(): void
     {
         $srcDirName = 'test_src_dir';
         $files = [
@@ -191,7 +192,7 @@ class FileHelperTest extends TestCase
         }
     }
 
-    public function testCopyDirectoryRecursive()
+    public function testCopyDirectoryRecursive(): void
     {
         $srcDirName = 'test_src_dir_rec';
         $structure = [
@@ -232,7 +233,7 @@ class FileHelperTest extends TestCase
         $checker($structure, $dstDirName);
     }
 
-    public function testCopyDirectoryNotRecursive()
+    public function testCopyDirectoryNotRecursive(): void
     {
         $srcDirName = 'test_src_dir_not_rec';
         $structure = [
@@ -273,7 +274,7 @@ class FileHelperTest extends TestCase
     /**
      * @depends testCopyDirectory
      */
-    public function testCopyDirectoryPermissions()
+    public function testCopyDirectoryPermissions(): void
     {
         if (DIRECTORY_SEPARATOR === '\\') {
             $this->markTestSkipped("Can't reliably test it on Windows because fileperms() always return 0777.");
@@ -309,7 +310,7 @@ class FileHelperTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/10710
      */
-    public function testCopyDirectoryToItself()
+    public function testCopyDirectoryToItself(): void
     {
         $dirName = 'test_dir';
 
@@ -326,7 +327,7 @@ class FileHelperTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/10710
      */
-    public function testCopyDirToSubdirOfItself()
+    public function testCopyDirToSubdirOfItself(): void
     {
         $this->createFileStructure([
             'data' => [],
@@ -344,7 +345,7 @@ class FileHelperTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/10710
      */
-    public function testCopyDirToAnotherWithSameName()
+    public function testCopyDirToAnotherWithSameName(): void
     {
         $this->createFileStructure([
             'data' => [],
@@ -361,7 +362,7 @@ class FileHelperTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/10710
      */
-    public function testCopyDirWithSameName()
+    public function testCopyDirWithSameName(): void
     {
         $this->createFileStructure([
             'data' => [],
@@ -376,7 +377,7 @@ class FileHelperTest extends TestCase
         $this->assertTrue(true);
     }
 
-    public function testRemoveDirectory()
+    public function testRemoveDirectory(): void
     {
         $dirName = 'test_dir_for_remove';
         $this->createFileStructure([
@@ -401,7 +402,7 @@ class FileHelperTest extends TestCase
         FileHelper::removeDirectory($basePath . DIRECTORY_SEPARATOR . 'nonExisting');
     }
 
-    public function testRemoveDirectorySymlinks1()
+    public function testRemoveDirectorySymlinks1(): void
     {
         if (DIRECTORY_SEPARATOR === '\\') {
             $this->markTestSkipped('Cannot test this on MS Windows since symlinks are uncommon for it.');
@@ -444,7 +445,7 @@ class FileHelperTest extends TestCase
         $this->assertFileDoesNotExist($basePath . 'symlinks' . DIRECTORY_SEPARATOR . 'symlinked-directory' . DIRECTORY_SEPARATOR . 'standard-file-1');
     }
 
-    public function testRemoveDirectorySymlinks2()
+    public function testRemoveDirectorySymlinks2(): void
     {
         if (DIRECTORY_SEPARATOR === '\\') {
             $this->markTestSkipped('Cannot test this on MS Windows since symlinks are uncommon for it.');
@@ -487,7 +488,7 @@ class FileHelperTest extends TestCase
         $this->assertFileDoesNotExist($basePath . 'symlinks' . DIRECTORY_SEPARATOR . 'symlinked-directory' . DIRECTORY_SEPARATOR . 'standard-file-1');
     }
 
-    public function testFindFiles()
+    public function testFindFiles(): void
     {
         $dirName = 'test_dir';
         $this->createFileStructure([
@@ -518,7 +519,7 @@ class FileHelperTest extends TestCase
     /**
      * @depends testFindFiles
      */
-    public function testFindFileFilter()
+    public function testFindFileFilter(): void
     {
         $dirName = 'test_dir';
         $passedFileName = 'passed.txt';
@@ -543,7 +544,7 @@ class FileHelperTest extends TestCase
     /**
      * @depends testFindFiles
      */
-    public function testFindFilesRecursiveWithSymLink()
+    public function testFindFilesRecursiveWithSymLink(): void
     {
         $dirName = 'test_dir';
         $this->createFileStructure([
@@ -571,7 +572,7 @@ class FileHelperTest extends TestCase
     /**
      * @depends testFindFiles
      */
-    public function testFindFilesNotRecursive()
+    public function testFindFilesNotRecursive(): void
     {
         $dirName = 'test_dir';
         $this->createFileStructure([
@@ -595,7 +596,7 @@ class FileHelperTest extends TestCase
     /**
      * @depends testFindFiles
      */
-    public function testFindFilesExclude()
+    public function testFindFilesExclude(): void
     {
         $basePath = $this->testFilePath . DIRECTORY_SEPARATOR;
         $dirs = ['', 'one', 'one' . DIRECTORY_SEPARATOR . 'two', 'three'];
@@ -673,7 +674,7 @@ class FileHelperTest extends TestCase
     /**
      * @depends testFindFilesExclude
      */
-    public function testFindFilesCaseSensitive()
+    public function testFindFilesCaseSensitive(): void
     {
         $dirName = 'test_dir';
         $this->createFileStructure([
@@ -700,7 +701,7 @@ class FileHelperTest extends TestCase
         $this->assertCount(2, $foundFiles);
     }
 
-    public function testGetMimeTypeByExtension()
+    public function testGetMimeTypeByExtension(): void
     {
         $magicFile = $this->testFilePath . DIRECTORY_SEPARATOR . 'mime_type.php';
         $mimeTypeMap = [
@@ -717,7 +718,7 @@ class FileHelperTest extends TestCase
         }
     }
 
-    public function testGetMimeType()
+    public function testGetMimeType(): void
     {
         $file = $this->testFilePath . DIRECTORY_SEPARATOR . 'mime_type_test.txt';
         file_put_contents($file, 'some text');
@@ -732,7 +733,7 @@ class FileHelperTest extends TestCase
         $this->assertTrue(in_array(FileHelper::getMimeType($file), ['application/json', 'text/plain']));
     }
 
-    public function testGetUploadedImageMimeTypes()
+    public function testGetUploadedImageMimeTypes(): void
     {
         $ds = DIRECTORY_SEPARATOR;
         $phpunitPath = Yii::getAlias('@yiiunit');
@@ -750,7 +751,7 @@ class FileHelperTest extends TestCase
         $this->assertEquals('image/jpeg', FileHelper::getMimeType($jpgFile));
     }
 
-    public function testNormalizePath()
+    public function testNormalizePath(): void
     {
         $ds = DIRECTORY_SEPARATOR;
         $this->assertEquals("{$ds}a{$ds}b", FileHelper::normalizePath('//a\b/'));
@@ -784,7 +785,7 @@ class FileHelperTest extends TestCase
         $this->assertEquals('ftp://192.168.1.100/test', FileHelper::normalizePath('ftp://192.168.1.100/test/'));
     }
 
-    public function testLocalizedDirectory()
+    public function testLocalizedDirectory(): void
     {
         $this->createFileStructure([
             'views' => [
@@ -815,7 +816,7 @@ class FileHelperTest extends TestCase
      * @depends testCopyDirectory
      * @depends testFindFiles
      */
-    public function testCopyDirectoryExclude()
+    public function testCopyDirectoryExclude(): void
     {
         $srcDirName = 'test_src_dir';
         $textFiles = [
@@ -876,7 +877,7 @@ class FileHelperTest extends TestCase
      * @depends testCopyDirectory
      * @depends testFindFiles
      */
-    public function testCopyDirectoryEmptyDirectories()
+    public function testCopyDirectoryEmptyDirectories(): void
     {
         list($basePath, $srcDirName) = $this->setupCopyEmptyDirectoriesTest();
 
@@ -901,7 +902,7 @@ class FileHelperTest extends TestCase
      * @depends testCopyDirectory
      * @depends testFindFiles
      */
-    public function testCopyDirectoryNoEmptyDirectories()
+    public function testCopyDirectoryNoEmptyDirectories(): void
     {
         list($basePath, $srcDirName) = $this->setupCopyEmptyDirectoriesTest();
 
@@ -920,7 +921,7 @@ class FileHelperTest extends TestCase
         $this->assertFileDoesNotExist($dstDirName . DIRECTORY_SEPARATOR . 'dir3');
     }
 
-    public function testFindDirectories()
+    public function testFindDirectories(): void
     {
         $dirName = 'test_dir';
         $this->createFileStructure([
@@ -972,7 +973,7 @@ class FileHelperTest extends TestCase
         $this->assertEquals($expectedFiles, $foundFiles);
     }
 
-    public function testChangeOwnership()
+    public function testChangeOwnership(): void
     {
         if (DIRECTORY_SEPARATOR !== '/') {
             $this->markTestSkipped('FileHelper::changeOwnership() fails silently on Windows, nothing to test.');
@@ -1221,7 +1222,7 @@ class FileHelperTest extends TestCase
         $this->assertEquals('0' . decoct($fileMode), substr(decoct(fileperms($testFile)), -4), 'Expected created test file mode to be changed.');
     }
 
-    public function testChangeOwnershipNonExistingUser()
+    public function testChangeOwnershipNonExistingUser(): void
     {
         $dirName = 'change_ownership_non_existing_user';
         $fileName = 'file_1.txt';
@@ -1237,8 +1238,8 @@ class FileHelperTest extends TestCase
         $ownership = 'non_existing_user';
         try {
             FileHelper::changeOwnership($testFile, $ownership);
-            throw new \Exception('FileHelper::changeOwnership() should have thrown error for non existing user.');
-        } catch (\Exception $e) {
+            throw new Exception('FileHelper::changeOwnership() should have thrown error for non existing user.');
+        } catch (Exception $e) {
             $this->assertEquals('chown(): Unable to find uid for non_existing_user', $e->getMessage());
         }
     }
@@ -1249,7 +1250,7 @@ class FileHelperTest extends TestCase
      * @param mixed $ownership
      * @param mixed $mode
      */
-    public function testChangeOwnershipInvalidArguments($useFile, $ownership, $mode)
+    public function testChangeOwnershipInvalidArguments($useFile, $ownership, $mode): void
     {
         $dirName = 'change_ownership_invalid_arguments';
         $fileName = 'file_1.txt';
@@ -1282,7 +1283,7 @@ class FileHelperTest extends TestCase
      * @param array $extensions
      * @return void
      */
-    public function testGetExtensionsByMimeType($mimeType, $extensions)
+    public function testGetExtensionsByMimeType($mimeType, $extensions): void
     {
         $this->assertEquals($extensions, FileHelper::getExtensionsByMimeType($mimeType));
     }
@@ -1317,7 +1318,7 @@ class FileHelperTest extends TestCase
      * @param array $extension
      * @return void
      */
-    public function testGetExtensionByMimeType($mimeType, $preferShort, $extension)
+    public function testGetExtensionByMimeType($mimeType, $preferShort, $extension): void
     {
         $this->assertEquals($extension, FileHelper::getExtensionByMimeType($mimeType, $preferShort));
     }
diff --git a/tests/framework/helpers/FormatConverterTest.php b/tests/framework/helpers/FormatConverterTest.php
index b18bf50c58..728dbc239d 100644
--- a/tests/framework/helpers/FormatConverterTest.php
+++ b/tests/framework/helpers/FormatConverterTest.php
@@ -38,13 +38,13 @@ class FormatConverterTest extends TestCase
         IntlTestHelper::resetIntlStatus();
     }
 
-    public function testIntlIcuToPhpShortForm()
+    public function testIntlIcuToPhpShortForm(): void
     {
         $this->assertEqualsAnyWhitespace('n/j/y', FormatConverter::convertDateIcuToPhp('short', 'date', 'en-US'));
         $this->assertEqualsAnyWhitespace('d.m.y', FormatConverter::convertDateIcuToPhp('short', 'date', 'de-DE'));
     }
 
-    public function testIntlIcuToPhpShortFormDefaultLang()
+    public function testIntlIcuToPhpShortFormDefaultLang(): void
     {
         Yii::$app->language = 'en';
         $this->assertEquals('n/j/y', FormatConverter::convertDateIcuToPhp('short', 'date'));
@@ -52,13 +52,13 @@ class FormatConverterTest extends TestCase
         $this->assertEquals('d.m.y', FormatConverter::convertDateIcuToPhp('short', 'date'));
     }
 
-    public function testIntlIcuToPhpShortFormTime()
+    public function testIntlIcuToPhpShortFormTime(): void
     {
         $this->assertEqualsAnyWhitespace('g:i A', FormatConverter::convertDateIcuToPhp('short', 'time', 'en-US'));
         $this->assertEqualsAnyWhitespace('H:i', FormatConverter::convertDateIcuToPhp('short', 'time', 'de-DE'));
     }
 
-    public function testIntlIcuToPhpShortFormDateTime()
+    public function testIntlIcuToPhpShortFormDateTime(): void
     {
         $this->assertEqualsAnyWhitespace('n/j/y, g:i A', FormatConverter::convertDateIcuToPhp('short', 'datetime', 'en-US'));
         $this->assertEquals(
@@ -67,7 +67,7 @@ class FormatConverterTest extends TestCase
         );
     }
 
-    public function testEscapedIcuToPhpMixedPatterns()
+    public function testEscapedIcuToPhpMixedPatterns(): void
     {
         $this->assertEquals('l, F j, Y \\a\\t g:i:s A T', FormatConverter::convertDateIcuToPhp('EEEE, MMMM d, y \'at\' h:mm:ss a zzzz'));
         $this->assertEquals('\\o\\\'\\c\\l\\o\\c\\k', FormatConverter::convertDateIcuToPhp('\'o\'\'clock\''));
@@ -182,24 +182,24 @@ class FormatConverterTest extends TestCase
     /**
      * @dataProvider providerForICU2PHPPatterns
      */
-    public function testEscapedIcuToPhpSinglePattern($pattern, $expected)
+    public function testEscapedIcuToPhpSinglePattern($pattern, $expected): void
     {
         $this->assertEquals($expected, FormatConverter::convertDateIcuToPhp($pattern));
     }
 
-    public function testEscapedIcuToJui()
+    public function testEscapedIcuToJui(): void
     {
         $this->assertEquals('DD, MM d, yy \'at\' ', FormatConverter::convertDateIcuToJui('EEEE, MMMM d, y \'at\' zzzz'));
         $this->assertEquals('\'o\'\'clock\'', FormatConverter::convertDateIcuToJui('\'o\'\'clock\''));
     }
 
-    public function testIntlIcuToJuiShortForm()
+    public function testIntlIcuToJuiShortForm(): void
     {
         $this->assertEquals('m/d/y', FormatConverter::convertDateIcuToJui('short', 'date', 'en-US'));
         $this->assertEquals('dd.mm.y', FormatConverter::convertDateIcuToJui('short', 'date', 'de-DE'));
     }
 
-    public function testIntlIcuToJuiShortFormDefaultLang()
+    public function testIntlIcuToJuiShortFormDefaultLang(): void
     {
         Yii::$app->language = 'en';
         $this->assertEquals('m/d/y', FormatConverter::convertDateIcuToJui('short', 'date'));
@@ -207,13 +207,13 @@ class FormatConverterTest extends TestCase
         $this->assertEquals('dd.mm.y', FormatConverter::convertDateIcuToJui('short', 'date'));
     }
 
-    public function testIntlIcuToJuiShortFormTime()
+    public function testIntlIcuToJuiShortFormTime(): void
     {
         $this->assertEqualsAnyWhitespace(': ', FormatConverter::convertDateIcuToJui('short', 'time', 'en-US'));
         $this->assertEqualsAnyWhitespace(':', FormatConverter::convertDateIcuToJui('short', 'time', 'de-DE'));
     }
 
-    public function testIntlIcuToJuiShortFormDateTime()
+    public function testIntlIcuToJuiShortFormDateTime(): void
     {
         $this->assertEqualsAnyWhitespace('m/d/y, : ', FormatConverter::convertDateIcuToJui('short', 'datetime', 'en-US'));
         $this->assertEquals(
@@ -330,12 +330,12 @@ class FormatConverterTest extends TestCase
     /**
      * @dataProvider providerForICU2JUIPatterns
      */
-    public function testEscapedIcuToJuiSinglePattern($pattern, $expected)
+    public function testEscapedIcuToJuiSinglePattern($pattern, $expected): void
     {
         $this->assertEquals($expected, FormatConverter::convertDateIcuToJui($pattern));
     }
 
-    public function testIntlOneDigitIcu()
+    public function testIntlOneDigitIcu(): void
     {
         $formatter = new Formatter(['locale' => 'en-US']);
         $this->assertEquals('24.8.2014', $formatter->asDate('2014-8-24', 'php:d.n.Y'));
@@ -343,7 +343,7 @@ class FormatConverterTest extends TestCase
         $this->assertEquals('24.8.2014', $formatter->asDate('2014-8-24', 'd.L.yyyy'));
     }
 
-    public function testOneDigitIcu()
+    public function testOneDigitIcu(): void
     {
         $formatter = new Formatter(['locale' => 'en-US']);
         $this->assertEquals('24.8.2014', $formatter->asDate('2014-8-24', 'php:d.n.Y'));
@@ -351,7 +351,7 @@ class FormatConverterTest extends TestCase
         $this->assertEquals('24.8.2014', $formatter->asDate('2014-8-24', 'd.L.yyyy'));
     }
 
-    public function testIntlUtf8Ru()
+    public function testIntlUtf8Ru(): void
     {
         $this->assertEquals('d M Y \г.', FormatConverter::convertDateIcuToPhp("dd MMM y 'г'.", 'date', 'ru-RU'));
         $this->assertEquals("dd M yy 'г'.", FormatConverter::convertDateIcuToJui("dd MMM y 'г'.", 'date', 'ru-RU'));
@@ -362,7 +362,7 @@ class FormatConverterTest extends TestCase
         $this->assertMatchesRegularExpression('/24 авг\.? 2014 г\./', $formatter->asDate('2014-8-24', "dd MMM y 'г'."));
     }
 
-    public function testPhpToICUMixedPatterns()
+    public function testPhpToICUMixedPatterns(): void
     {
         $expected = "yyyy-MM-dd'T'HH:mm:ssxxx";
         $actual = FormatConverter::convertDatePhpToIcu('Y-m-d\TH:i:sP');
@@ -475,12 +475,12 @@ class FormatConverterTest extends TestCase
     /**
      * @dataProvider providerForPHP2ICUPatterns
      */
-    public function testPhpToICUSinglePattern($pattern, $expected)
+    public function testPhpToICUSinglePattern($pattern, $expected): void
     {
         $this->assertEquals($expected, FormatConverter::convertDatePhpToIcu($pattern));
     }
 
-    public function testPhpFormatC()
+    public function testPhpFormatC(): void
     {
         $time = time();
 
@@ -492,7 +492,7 @@ class FormatConverterTest extends TestCase
         $this->assertEquals(date('c', $time), $formatter->asDatetime($time, 'php:c'));
     }
 
-    public function testEscapedPhpToJuiMixedPatterns()
+    public function testEscapedPhpToJuiMixedPatterns(): void
     {
         $this->assertEquals('dd-mm-yy', FormatConverter::convertDatePhpToJui('d-m-Y'));
     }
@@ -543,7 +543,7 @@ class FormatConverterTest extends TestCase
     /**
      * @dataProvider providerForPHP2JUIPatterns
      */
-    public function testEscapedPhpToJuiSinglePattern($pattern, $expected)
+    public function testEscapedPhpToJuiSinglePattern($pattern, $expected): void
     {
         $this->assertEquals($expected, FormatConverter::convertDatePhpToJui($pattern));
     }
diff --git a/tests/framework/helpers/HtmlTest.php b/tests/framework/helpers/HtmlTest.php
index 440f9f156d..0b1fe156a5 100644
--- a/tests/framework/helpers/HtmlTest.php
+++ b/tests/framework/helpers/HtmlTest.php
@@ -8,6 +8,10 @@
 
 namespace yiiunit\framework\helpers;
 
+use ArrayObject;
+use yii\base\InvalidArgumentException;
+use Closure;
+use yii\base\Model;
 use Yii;
 use yii\base\DynamicModel;
 use yii\db\ArrayExpression;
@@ -39,18 +43,18 @@ class HtmlTest extends TestCase
         ]);
     }
 
-    public function testEncode()
+    public function testEncode(): void
     {
         $this->assertEquals('a&lt;&gt;&amp;&quot;&#039;�', Html::encode("a<>&\"'\x80"));
         $this->assertEquals('Sam &amp; Dark', Html::encode('Sam & Dark'));
     }
 
-    public function testDecode()
+    public function testDecode(): void
     {
         $this->assertEquals("a<>&\"'", Html::decode('a&lt;&gt;&amp;&quot;&#039;'));
     }
 
-    public function testTag()
+    public function testTag(): void
     {
         $this->assertEquals('<br>', Html::tag('br'));
         $this->assertEquals('<span></span>', Html::tag('span'));
@@ -61,7 +65,7 @@ class HtmlTest extends TestCase
         $this->assertEquals('test', Html::tag(null, 'test'));
     }
 
-    public function testBeginTag()
+    public function testBeginTag(): void
     {
         $this->assertEquals('<br>', Html::beginTag('br'));
         $this->assertEquals('<span id="test" class="title">', Html::beginTag('span', ['id' => 'test', 'class' => 'title']));
@@ -69,7 +73,7 @@ class HtmlTest extends TestCase
         $this->assertEquals('', Html::beginTag(false));
     }
 
-    public function testEndTag()
+    public function testEndTag(): void
     {
         $this->assertEquals('</br>', Html::endTag('br'));
         $this->assertEquals('</span>', Html::endTag('span'));
@@ -77,14 +81,14 @@ class HtmlTest extends TestCase
         $this->assertEquals('', Html::endTag(false));
     }
 
-    public function testStyle()
+    public function testStyle(): void
     {
         $content = 'a <>';
         $this->assertEquals("<style>{$content}</style>", Html::style($content));
         $this->assertEquals("<style type=\"text/less\">{$content}</style>", Html::style($content, ['type' => 'text/less']));
     }
 
-    public function testStyleCustomAttribute()
+    public function testStyleCustomAttribute(): void
     {
         $nonce = Yii::$app->security->generateRandomString();
         $this->mockApplication([
@@ -99,14 +103,14 @@ class HtmlTest extends TestCase
         $this->assertEquals("<style nonce=\"{$nonce}\">{$content}</style>", Html::style($content));
     }
 
-    public function testScript()
+    public function testScript(): void
     {
         $content = 'a <>';
         $this->assertEquals("<script>{$content}</script>", Html::script($content));
         $this->assertEquals("<script type=\"text/js\">{$content}</script>", Html::script($content, ['type' => 'text/js']));
     }
 
-    public function testScriptCustomAttribute()
+    public function testScriptCustomAttribute(): void
     {
         $nonce = Yii::$app->security->generateRandomString();
         $this->mockApplication([
@@ -121,7 +125,7 @@ class HtmlTest extends TestCase
         $this->assertEquals("<script nonce=\"{$nonce}\">{$content}</script>", Html::script($content));
     }
 
-    public function testCssFile()
+    public function testCssFile(): void
     {
         $this->assertEquals('<link href="http://example.com" rel="stylesheet">', Html::cssFile('http://example.com'));
         $this->assertEquals('<link href="/test" rel="stylesheet">', Html::cssFile(''));
@@ -130,7 +134,7 @@ class HtmlTest extends TestCase
         $this->assertEquals('<noscript><link href="http://example.com" rel="stylesheet"></noscript>', Html::cssFile('http://example.com', ['noscript' => true]));
     }
 
-    public function testJsFile()
+    public function testJsFile(): void
     {
         $this->assertEquals('<script src="http://example.com"></script>', Html::jsFile('http://example.com'));
         $this->assertEquals('<script src="/test"></script>', Html::jsFile(''));
@@ -138,7 +142,7 @@ class HtmlTest extends TestCase
         $this->assertEquals("<!--[if (gte IE 9)|(!IE)]><!-->\n" . '<script src="http://example.com"></script>' . "\n<!--<![endif]-->", Html::jsFile('http://example.com', ['condition' => '(gte IE 9)|(!IE)']));
     }
 
-    public function testCsrfMetaTagsDisableCsrfValidation()
+    public function testCsrfMetaTagsDisableCsrfValidation(): void
     {
         $this->mockApplication([
             'components' => [
@@ -151,7 +155,7 @@ class HtmlTest extends TestCase
         $this->assertEquals('', Html::csrfMetaTags());
     }
 
-    public function testCsrfMetaTagsEnableCsrfValidation()
+    public function testCsrfMetaTagsEnableCsrfValidation(): void
     {
         $this->mockApplication([
             'components' => [
@@ -170,7 +174,7 @@ class HtmlTest extends TestCase
         $this->assertStringMatchesFormat($pattern, $actual);
     }
 
-    public function testCsrfMetaTagsEnableCsrfValidationWithoutCookieValidationKey()
+    public function testCsrfMetaTagsEnableCsrfValidationWithoutCookieValidationKey(): void
     {
         $this->mockApplication([
             'components' => [
@@ -191,7 +195,7 @@ class HtmlTest extends TestCase
      * @param string $expected
      * @param string $method
      */
-    public function testBeginFormSimulateViaPost($expected, $method)
+    public function testBeginFormSimulateViaPost($expected, $method): void
     {
         $actual = Html::beginForm('/foo', $method);
         $this->assertStringMatchesFormat($expected, $actual);
@@ -213,7 +217,7 @@ class HtmlTest extends TestCase
         ];
     }
 
-    public function testBeginForm()
+    public function testBeginForm(): void
     {
         $this->assertEquals('<form action="/test" method="post">', Html::beginForm());
         $this->assertEquals('<form action="/example" method="get">', Html::beginForm('/example', 'get'));
@@ -228,12 +232,12 @@ class HtmlTest extends TestCase
         $this->assertStringMatchesFormat($expected, $actual);
     }
 
-    public function testEndForm()
+    public function testEndForm(): void
     {
         $this->assertEquals('</form>', Html::endForm());
     }
 
-    public function testA()
+    public function testA(): void
     {
         $this->assertEquals('<a>something<></a>', Html::a('something<>'));
         $this->assertEquals('<a href="/example">something</a>', Html::a('something', '/example'));
@@ -242,7 +246,7 @@ class HtmlTest extends TestCase
         $this->assertEquals('<a href="https://www.example.com/index.php?r=site%2Ftest">Test page</a>', Html::a('Test page', Url::to(['/site/test'], 'https')));
     }
 
-    public function testMailto()
+    public function testMailto(): void
     {
         $this->assertEquals('<a href="mailto:test&lt;&gt;">test<></a>', Html::mailto('test<>'));
         $this->assertEquals('<a href="mailto:test&gt;">test<></a>', Html::mailto('test<>', 'test>'));
@@ -340,80 +344,80 @@ class HtmlTest extends TestCase
      * @param string $src
      * @param array $options
      */
-    public function testImg($expected, $src, $options)
+    public function testImg($expected, $src, $options): void
     {
         $this->assertEquals($expected, Html::img($src, $options));
     }
 
-    public function testLabel()
+    public function testLabel(): void
     {
         $this->assertEquals('<label>something<></label>', Html::label('something<>'));
         $this->assertEquals('<label for="a">something<></label>', Html::label('something<>', 'a'));
         $this->assertEquals('<label class="test" for="a">something<></label>', Html::label('something<>', 'a', ['class' => 'test']));
     }
 
-    public function testButton()
+    public function testButton(): void
     {
         $this->assertEquals('<button type="button">Button</button>', Html::button());
         $this->assertEquals('<button type="button" name="test" value="value">content<></button>', Html::button('content<>', ['name' => 'test', 'value' => 'value']));
         $this->assertEquals('<button type="submit" class="t" name="test" value="value">content<></button>', Html::button('content<>', ['type' => 'submit', 'name' => 'test', 'value' => 'value', 'class' => 't']));
     }
 
-    public function testSubmitButton()
+    public function testSubmitButton(): void
     {
         $this->assertEquals('<button type="submit">Submit</button>', Html::submitButton());
         $this->assertEquals('<button type="submit" class="t" name="test" value="value">content<></button>', Html::submitButton('content<>', ['name' => 'test', 'value' => 'value', 'class' => 't']));
     }
 
-    public function testResetButton()
+    public function testResetButton(): void
     {
         $this->assertEquals('<button type="reset">Reset</button>', Html::resetButton());
         $this->assertEquals('<button type="reset" class="t" name="test" value="value">content<></button>', Html::resetButton('content<>', ['name' => 'test', 'value' => 'value', 'class' => 't']));
     }
 
-    public function testInput()
+    public function testInput(): void
     {
         $this->assertEquals('<input type="text">', Html::input('text'));
         $this->assertEquals('<input type="text" class="t" name="test" value="value">', Html::input('text', 'test', 'value', ['class' => 't']));
     }
 
-    public function testButtonInput()
+    public function testButtonInput(): void
     {
         $this->assertEquals('<input type="button" value="Button">', Html::buttonInput());
         $this->assertEquals('<input type="button" class="a" name="test" value="text">', Html::buttonInput('text', ['name' => 'test', 'class' => 'a']));
     }
 
-    public function testSubmitInput()
+    public function testSubmitInput(): void
     {
         $this->assertEquals('<input type="submit" value="Submit">', Html::submitInput());
         $this->assertEquals('<input type="submit" class="a" name="test" value="text">', Html::submitInput('text', ['name' => 'test', 'class' => 'a']));
     }
 
-    public function testResetInput()
+    public function testResetInput(): void
     {
         $this->assertEquals('<input type="reset" value="Reset">', Html::resetInput());
         $this->assertEquals('<input type="reset" class="a" name="test" value="text">', Html::resetInput('text', ['name' => 'test', 'class' => 'a']));
     }
 
-    public function testTextInput()
+    public function testTextInput(): void
     {
         $this->assertEquals('<input type="text" name="test">', Html::textInput('test'));
         $this->assertEquals('<input type="text" class="t" name="test" value="value">', Html::textInput('test', 'value', ['class' => 't']));
     }
 
-    public function testHiddenInput()
+    public function testHiddenInput(): void
     {
         $this->assertEquals('<input type="hidden" name="test">', Html::hiddenInput('test'));
         $this->assertEquals('<input type="hidden" class="t" name="test" value="value">', Html::hiddenInput('test', 'value', ['class' => 't']));
     }
 
-    public function testPasswordInput()
+    public function testPasswordInput(): void
     {
         $this->assertEquals('<input type="password" name="test">', Html::passwordInput('test'));
         $this->assertEquals('<input type="password" class="t" name="test" value="value">', Html::passwordInput('test', 'value', ['class' => 't']));
     }
 
-    public function testFileInput()
+    public function testFileInput(): void
     {
         $this->assertEquals('<input type="file" name="test">', Html::fileInput('test'));
         $this->assertEquals('<input type="file" class="t" name="test" value="value">', Html::fileInput('test', 'value', ['class' => 't']));
@@ -459,12 +463,12 @@ class HtmlTest extends TestCase
      * @param string $value
      * @param array $options
      */
-    public function testTextarea($expected, $name, $value, $options)
+    public function testTextarea($expected, $name, $value, $options): void
     {
         $this->assertEquals($expected, Html::textarea($name, $value, $options));
     }
 
-    public function testRadio()
+    public function testRadio(): void
     {
         $this->assertEquals('<input type="radio" name="test" value="1">', Html::radio('test'));
         $this->assertEquals('<input type="radio" class="a" name="test" checked>', Html::radio('test', true, ['class' => 'a', 'value' => null]));
@@ -493,7 +497,7 @@ class HtmlTest extends TestCase
         ]));
     }
 
-    public function testCheckbox()
+    public function testCheckbox(): void
     {
         $this->assertEquals('<input type="checkbox" name="test" value="1">', Html::checkbox('test'));
         $this->assertEquals('<input type="checkbox" class="a" name="test" checked>', Html::checkbox('test', true, ['class' => 'a', 'value' => null]));
@@ -536,7 +540,7 @@ class HtmlTest extends TestCase
         ]));
     }
 
-    public function testDropDownList()
+    public function testDropDownList(): void
     {
         $expected = <<<'EOD'
 <select name="test">
@@ -589,7 +593,7 @@ EOD;
         );
         $this->assertEqualsWithoutLE(
             $expected,
-            Html::dropDownList('test', new \ArrayObject([0]), $this->getDataItems3(), ['multiple' => 'true'])
+            Html::dropDownList('test', new ArrayObject([0]), $this->getDataItems3(), ['multiple' => 'true'])
         );
 
         $expected = <<<'EOD'
@@ -607,7 +611,7 @@ EOD;
             $expected,
             Html::dropDownList(
                 'test',
-                new \ArrayObject(['1', 'value3']),
+                new ArrayObject(['1', 'value3']),
                 $this->getDataItems3(),
                 ['multiple' => 'true']
             )
@@ -631,7 +635,7 @@ EOD;
     /**
      * @dataProvider providerForNonStrictBooleanDropDownList
      */
-    public function testNonStrictBooleanDropDownList($selection, $selectedEmpty, $selectedYes, $selectedNo)
+    public function testNonStrictBooleanDropDownList($selection, $selectedEmpty, $selectedYes, $selectedNo): void
     {
         $selectedEmpty = $selectedEmpty ? ' selected' : '';
         $selectedYes = $selectedYes ? ' selected' : '';
@@ -666,7 +670,7 @@ HTML;
     /**
      * @dataProvider providerForStrictBooleanDropDownList
      */
-    public function testStrictBooleanDropDownList($selection, $selectedEmpty, $selectedYes, $selectedNo)
+    public function testStrictBooleanDropDownList($selection, $selectedEmpty, $selectedYes, $selectedNo): void
     {
         $selectedEmpty = $selectedEmpty ? ' selected' : '';
         $selectedYes = $selectedYes ? ' selected' : '';
@@ -684,7 +688,7 @@ HTML;
         );
     }
 
-    public function testListBox()
+    public function testListBox(): void
     {
         $expected = <<<'EOD'
 <select name="test" size="4">
@@ -770,7 +774,7 @@ EOD;
 <option value="value2" selected>text2</option>
 </select>
 EOD;
-        $this->assertEqualsWithoutLE($expected, Html::listBox('test', new \ArrayObject(['value1', 'value2']), $this->getDataItems()));
+        $this->assertEqualsWithoutLE($expected, Html::listBox('test', new ArrayObject(['value1', 'value2']), $this->getDataItems()));
 
         $expected = <<<'EOD'
 <select name="test" size="4">
@@ -780,7 +784,7 @@ EOD;
 </select>
 EOD;
         $this->assertEqualsWithoutLE($expected, Html::listBox('test', [0], $this->getDataItems3()));
-        $this->assertEqualsWithoutLE($expected, Html::listBox('test', new \ArrayObject([0]), $this->getDataItems3()));
+        $this->assertEqualsWithoutLE($expected, Html::listBox('test', new ArrayObject([0]), $this->getDataItems3()));
 
         $expected = <<<'EOD'
 <select name="test" size="4">
@@ -790,10 +794,10 @@ EOD;
 </select>
 EOD;
         $this->assertEqualsWithoutLE($expected, Html::listBox('test', ['1', 'value3'], $this->getDataItems3()));
-        $this->assertEqualsWithoutLE($expected, Html::listBox('test', new \ArrayObject(['1', 'value3']), $this->getDataItems3()));
+        $this->assertEqualsWithoutLE($expected, Html::listBox('test', new ArrayObject(['1', 'value3']), $this->getDataItems3()));
     }
 
-    public function testCheckboxList()
+    public function testCheckboxList(): void
     {
         $this->assertEquals('<div></div>', Html::checkboxList('test'));
 
@@ -851,7 +855,7 @@ EOD;
         ]));
 
 
-        $this->assertEqualsWithoutLE($expected, Html::checkboxList('test', new \ArrayObject(['value2']), $this->getDataItems(), [
+        $this->assertEqualsWithoutLE($expected, Html::checkboxList('test', new ArrayObject(['value2']), $this->getDataItems(), [
             'item' => function ($index, $label, $name, $checked, $value) {
                 return $index . Html::label($label . ' ' . Html::checkbox($name, $checked, ['value' => $value]));
             },
@@ -864,7 +868,7 @@ EOD;
 <label><input type="checkbox" name="test[]" value="value3"> text3</label></div>
 EOD;
         $this->assertEqualsWithoutLE($expected, Html::checkboxList('test', [0], $this->getDataItems3()));
-        $this->assertEqualsWithoutLE($expected, Html::checkboxList('test', new \ArrayObject([0]), $this->getDataItems3()));
+        $this->assertEqualsWithoutLE($expected, Html::checkboxList('test', new ArrayObject([0]), $this->getDataItems3()));
 
         $expected = <<<'EOD'
 <div><label><input type="checkbox" name="test[]" value="0"> zero</label>
@@ -872,7 +876,7 @@ EOD;
 <label><input type="checkbox" name="test[]" value="value3" checked> text3</label></div>
 EOD;
         $this->assertEqualsWithoutLE($expected, Html::checkboxList('test', ['1', 'value3'], $this->getDataItems3()));
-        $this->assertEqualsWithoutLE($expected, Html::checkboxList('test', new \ArrayObject(['1', 'value3']), $this->getDataItems3()));
+        $this->assertEqualsWithoutLE($expected, Html::checkboxList('test', new ArrayObject(['1', 'value3']), $this->getDataItems3()));
 
         $expected = <<<'EOD'
 <div><label><input type="checkbox" name="test[]" value="0"> Test Label</label>
@@ -901,7 +905,7 @@ EOD;
         $this->assertEqualsWithoutLE($expected, Html::checkboxList('test', [1.1], ['1' => '1', '1.1' => '1.1', '1.10' => '1.10']));
     }
 
-    public function testRadioListWithArrayExpression()
+    public function testRadioListWithArrayExpression(): void
     {
         $selection = new ArrayExpression(['first']);
 
@@ -918,7 +922,7 @@ EOD;
 <label><input type="radio" name="test" value="second"> second</label></div>', $output);
     }
 
-    public function testCheckboxListWithArrayExpression()
+    public function testCheckboxListWithArrayExpression(): void
     {
         $selection = new ArrayExpression(['first']);
 
@@ -935,7 +939,7 @@ EOD;
 <label><input type="checkbox" name="test[]" value="second"> second</label></div>', $output);
     }
 
-    public function testRenderSelectOptionsWithArrayExpression()
+    public function testRenderSelectOptionsWithArrayExpression(): void
     {
         $selection = new ArrayExpression(['first']);
 
@@ -951,7 +955,7 @@ EOD;
 <option value="second">second</option>', $output);
     }
 
-    public function testRadioList()
+    public function testRadioList(): void
     {
         $this->assertEquals('<div></div>', Html::radioList('test'));
 
@@ -1007,7 +1011,7 @@ EOD;
             'tag' => false,
         ]));
 
-        $this->assertEqualsWithoutLE($expected, Html::radioList('test', new \ArrayObject(['value2']), $this->getDataItems(), [
+        $this->assertEqualsWithoutLE($expected, Html::radioList('test', new ArrayObject(['value2']), $this->getDataItems(), [
             'item' => function ($index, $label, $name, $checked, $value) {
                 return $index . Html::label($label . ' ' . Html::radio($name, $checked, ['value' => $value]));
             },
@@ -1020,7 +1024,7 @@ EOD;
 <label><input type="radio" name="test" value="value3"> text3</label></div>
 EOD;
         $this->assertEqualsWithoutLE($expected, Html::radioList('test', [0], $this->getDataItems3()));
-        $this->assertEqualsWithoutLE($expected, Html::radioList('test', new \ArrayObject([0]), $this->getDataItems3()));
+        $this->assertEqualsWithoutLE($expected, Html::radioList('test', new ArrayObject([0]), $this->getDataItems3()));
 
         $expected = <<<'EOD'
 <div><label><input type="radio" name="test" value="0"> zero</label>
@@ -1028,7 +1032,7 @@ EOD;
 <label><input type="radio" name="test" value="value3" checked> text3</label></div>
 EOD;
         $this->assertEqualsWithoutLE($expected, Html::radioList('test', ['value3'], $this->getDataItems3()));
-        $this->assertEqualsWithoutLE($expected, Html::radioList('test', new \ArrayObject(['value3']), $this->getDataItems3()));
+        $this->assertEqualsWithoutLE($expected, Html::radioList('test', new ArrayObject(['value3']), $this->getDataItems3()));
 
         $expected = <<<'EOD'
 <div><label><input type="radio" name="test" value="0"> Test Label</label>
@@ -1057,7 +1061,7 @@ EOD;
         $this->assertEqualsWithoutLE($expected, Html::radioList('test', ['1.1'], ['1' => '1', '1.1' => '1.1', '1.10' => '1.10']));
     }
 
-    public function testUl()
+    public function testUl(): void
     {
         $data = [
             1, 'abc', '<>',
@@ -1089,7 +1093,7 @@ EOD;
         $this->assertStringMatchesFormat('<foo>%A</foo>', Html::ul([], ['tag' => 'foo']));
     }
 
-    public function testOl()
+    public function testOl(): void
     {
         $data = [
             1, 'abc', '<>',
@@ -1121,7 +1125,7 @@ EOD;
         $this->assertEquals('<ol class="test"></ol>', Html::ol([], ['class' => 'test']));
     }
 
-    public function testRenderOptions()
+    public function testRenderOptions(): void
     {
         $data = [
             'value1' => 'label1',
@@ -1239,7 +1243,7 @@ EOD;
         $this->assertEqualsWithoutLE($expected, Html::renderSelectOptions([false], $data, $attributes));
     }
 
-    public function testRenderTagAttributes()
+    public function testRenderTagAttributes(): void
     {
         $this->assertEquals('', Html::renderTagAttributes([]));
         $this->assertEquals(' name="test" value="1&lt;&gt;"', Html::renderTagAttributes(['name' => 'test', 'empty' => null, 'value' => '1<>']));
@@ -1282,7 +1286,7 @@ EOD;
         $this->assertEquals('', Html::renderTagAttributes($attributes));
     }
 
-    public function testAddCssClass()
+    public function testAddCssClass(): void
     {
         $options = [];
         Html::addCssClass($options, 'test');
@@ -1320,7 +1324,7 @@ EOD;
     /**
      * @depends testAddCssClass
      */
-    public function testMergeCssClass()
+    public function testMergeCssClass(): void
     {
         $options = [
             'class' => [
@@ -1333,7 +1337,7 @@ EOD;
         $this->assertEquals(['persistent' => 'test1', 'additional' => 'test2'], $options['class']);
     }
 
-    public function testRemoveCssClass()
+    public function testRemoveCssClass(): void
     {
         $options = ['class' => 'test test2 test3'];
         Html::removeCssClass($options, 'test2');
@@ -1359,7 +1363,7 @@ EOD;
         $this->assertEquals(['class' => 'test'], $options);
     }
 
-    public function testCssStyleFromArray()
+    public function testCssStyleFromArray(): void
     {
         $this->assertEquals('width: 100px; height: 200px;', Html::cssStyleFromArray([
             'width' => '100px',
@@ -1368,7 +1372,7 @@ EOD;
         $this->assertNull(Html::cssStyleFromArray([]));
     }
 
-    public function testCssStyleToArray()
+    public function testCssStyleToArray(): void
     {
         $this->assertEquals([
             'width' => '100px',
@@ -1377,7 +1381,7 @@ EOD;
         $this->assertEquals([], Html::cssStyleToArray('  '));
     }
 
-    public function testAddCssStyle()
+    public function testAddCssStyle(): void
     {
         $options = ['style' => 'width: 100px; height: 200px;'];
         Html::addCssStyle($options, 'width: 110px; color: red;');
@@ -1408,7 +1412,7 @@ EOD;
         $this->assertEquals('width: 100px; color: red;', $options['style']);
     }
 
-    public function testRemoveCssStyle()
+    public function testRemoveCssStyle(): void
     {
         $options = ['style' => 'width: 110px; height: 200px; color: red;'];
         Html::removeCssStyle($options, 'width');
@@ -1431,14 +1435,14 @@ EOD;
         $this->assertEquals('width: 100px;', $options['style']);
     }
 
-    public function testBooleanAttributes()
+    public function testBooleanAttributes(): void
     {
         $this->assertEquals('<input type="email" name="mail">', Html::input('email', 'mail', null, ['required' => false]));
         $this->assertEquals('<input type="email" name="mail" required>', Html::input('email', 'mail', null, ['required' => true]));
         $this->assertEquals('<input type="email" name="mail" required="hi">', Html::input('email', 'mail', null, ['required' => 'hi']));
     }
 
-    public function testDataAttributes()
+    public function testDataAttributes(): void
     {
         $this->assertEquals('<link src="xyz" aria-a="1" aria-b="c">', Html::tag('link', '', ['src' => 'xyz', 'aria' => ['a' => 1, 'b' => 'c']]));
         $this->assertEquals('<link src="xyz" data-a="1" data-b="c">', Html::tag('link', '', ['src' => 'xyz', 'data' => ['a' => 1, 'b' => 'c']]));
@@ -1508,7 +1512,7 @@ EOD;
      * @param array $options
      * @param string $expectedHtml
      */
-    public function testActiveTextInput($value, array $options, $expectedHtml)
+    public function testActiveTextInput($value, array $options, $expectedHtml): void
     {
         $model = new HtmlTestModel();
         $model->name = $value;
@@ -1555,7 +1559,7 @@ EOD;
      * @param string $expectedHtmlForTitle
      * @param string $expectedHtmlForAlias
      */
-    public function testActiveTextInputMaxLength($value, array $options, $expectedHtmlForTitle, $expectedHtmlForAlias)
+    public function testActiveTextInputMaxLength($value, array $options, $expectedHtmlForTitle, $expectedHtmlForAlias): void
     {
         $model = new HtmlTestModel();
         $model->title = $value;
@@ -1600,7 +1604,7 @@ EOD;
      * @param array $options
      * @param string $expectedHtml
      */
-    public function testActivePasswordInput($value, array $options, $expectedHtml)
+    public function testActivePasswordInput($value, array $options, $expectedHtml): void
     {
         $model = new HtmlTestModel();
         $model->name = $value;
@@ -1643,7 +1647,7 @@ EOD;
      * @param array $options
      * @param string $expectedHtml
      */
-    public function testActiveInput_TypeText($value, array $options, $expectedHtml)
+    public function testActiveInput_TypeText($value, array $options, $expectedHtml): void
     {
         $model = new HtmlTestModel();
         $model->name = $value;
@@ -1716,9 +1720,9 @@ EOD;
      * @param string $value
      * @param array $options
      * @param string $expectedHtml
-     * @param \Closure $beforeValidate
+     * @param Closure $beforeValidate
      */
-    public function testErrorSummary($value, array $options, $expectedHtml, $beforeValidate = null)
+    public function testErrorSummary($value, array $options, $expectedHtml, $beforeValidate = null): void
     {
         $model = new HtmlTestModel();
         $model->name = $value;
@@ -1730,7 +1734,7 @@ EOD;
         $this->assertEqualsWithoutLE($expectedHtml, Html::errorSummary($model, $options));
     }
 
-    public function testError()
+    public function testError(): void
     {
         $model = new HtmlTestModel();
         $model->validate();
@@ -1758,7 +1762,7 @@ EOD;
      * Test that attributes that output same errors, return unique message error
      * @see https://github.com/yiisoft/yii2/pull/15859
      */
-    public function testCollectError()
+    public function testCollectError(): void
     {
         $model = new DynamicModel(['attr1', 'attr2']);
 
@@ -1816,7 +1820,7 @@ EOD;
      * @param array $options
      * @param string $expectedHtml
      */
-    public function testActiveTextArea($value, array $options, $expectedHtml)
+    public function testActiveTextArea($value, array $options, $expectedHtml): void
     {
         $model = new HtmlTestModel();
         $model->description = $value;
@@ -1826,7 +1830,7 @@ EOD;
     /**
      * @see https://github.com/yiisoft/yii2/issues/10078
      */
-    public function testCsrfDisable()
+    public function testCsrfDisable(): void
     {
         Yii::$app->request->enableCsrfValidation = true;
         Yii::$app->request->cookieValidationKey = 'foobar';
@@ -1879,7 +1883,7 @@ EOD;
      * @param array $options
      * @param string $expectedHtml
      */
-    public function testActiveRadio($value, array $options, $expectedHtml)
+    public function testActiveRadio($value, array $options, $expectedHtml): void
     {
         $model = new HtmlTestModel();
         $model->radio = $value;
@@ -1923,7 +1927,7 @@ EOD;
      * @param array $options
      * @param string $expectedHtml
      */
-    public function testActiveCheckbox($value, array $options, $expectedHtml)
+    public function testActiveCheckbox($value, array $options, $expectedHtml): void
     {
         $model = new HtmlTestModel();
         $model->checkbox = $value;
@@ -1975,7 +1979,7 @@ EOD;
      * @param string $name
      * @param string $expected
      */
-    public function testAttributeNameValidation($name, $expected)
+    public function testAttributeNameValidation($name, $expected): void
     {
         $this->assertEquals($expected, Html::getAttributeName($name));
     }
@@ -1985,14 +1989,14 @@ EOD;
      *
      * @param string $name
      */
-    public function testAttributeNameException($name)
+    public function testAttributeNameException($name): void
     {
         $this->expectException('yii\base\InvalidArgumentException');
 
         Html::getAttributeName($name);
     }
 
-    public function testActiveFileInput()
+    public function testActiveFileInput(): void
     {
         $expected = '<input type="hidden" name="foo" value=""><input type="file" id="htmltestmodel-types" name="foo">';
         $model = new HtmlTestModel();
@@ -2025,16 +2029,16 @@ EOD;
         $this->assertEqualsWithoutLE($expected, $actual);
     }
 
-    public function testGetAttributeValueInvalidArgumentException()
+    public function testGetAttributeValueInvalidArgumentException(): void
     {
-        $this->expectException(\yii\base\InvalidArgumentException::class);
+        $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Attribute name must contain word characters only.');
 
         $model = new HtmlTestModel();
         Html::getAttributeValue($model, '-');
     }
 
-    public function testGetAttributeValue()
+    public function testGetAttributeValue(): void
     {
         $model = new HtmlTestModel();
 
@@ -2059,28 +2063,28 @@ EOD;
         $this->assertSame($expected, $actual);
     }
 
-    public function testGetInputNameInvalidArgumentExceptionAttribute()
+    public function testGetInputNameInvalidArgumentExceptionAttribute(): void
     {
         $model = new HtmlTestModel();
 
-        $this->expectException(\yii\base\InvalidArgumentException::class);
+        $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Attribute name must contain word characters only.');
 
         Html::getInputName($model, '-');
     }
 
-    public function testGetInputNameInvalidArgumentExceptionFormName()
+    public function testGetInputNameInvalidArgumentExceptionFormName(): void
     {
         $model = $this->getMockBuilder('yii\\base\\Model')->getMock();
         $model->method('formName')->willReturn('');
 
-        $this->expectException(\yii\base\InvalidArgumentException::class);
+        $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('cannot be empty for tabular inputs.');
 
         Html::getInputName($model, '[foo]bar');
     }
 
-    public function testGetInputName()
+    public function testGetInputName(): void
     {
         $model = $this->getMockBuilder('yii\\base\\Model')->getMock();
         $model->method('formName')->willReturn('');
@@ -2092,7 +2096,7 @@ EOD;
     /**
      * @dataProvider getInputIdDataProvider
      */
-    public function testGetInputId($attributeName, $inputIdExpected)
+    public function testGetInputId($attributeName, $inputIdExpected): void
     {
         $model = new DynamicModel();
         $model->defineAttribute($attributeName);
@@ -2105,7 +2109,7 @@ EOD;
     /**
      * @dataProvider getInputIdByNameDataProvider
      */
-    public function testGetInputIdByName($attributeName, $inputIdExpected)
+    public function testGetInputIdByName($attributeName, $inputIdExpected): void
     {
         $model = new DynamicModel();
         $model->defineAttribute($attributeName);
@@ -2115,7 +2119,7 @@ EOD;
         $this->assertSame($inputIdExpected, $inputIdActual);
     }
 
-    public function testEscapeJsRegularExpression()
+    public function testEscapeJsRegularExpression(): void
     {
         $expected = '/[a-z0-9-]+/';
         $actual = Html::escapeJsRegularExpression('([a-z0-9-]+)');
@@ -2131,7 +2135,7 @@ EOD;
         $this->assertSame($expected, $actual);
     }
 
-    public function testActiveDropDownList()
+    public function testActiveDropDownList(): void
     {
         $expected = <<<'HTML'
 <input type="hidden" name="HtmlTestModel[types]" value=""><select id="htmltestmodel-types" name="HtmlTestModel[types][]" multiple="true" size="4">
@@ -2143,7 +2147,7 @@ HTML;
         $this->assertEqualsWithoutLE($expected, $actual);
     }
 
-    public function testActiveRadioList()
+    public function testActiveRadioList(): void
     {
         $model = new HtmlTestModel();
 
@@ -2154,7 +2158,7 @@ HTML;
         $this->assertEqualsWithoutLE($expected, $actual);
     }
 
-    public function testActiveCheckboxList()
+    public function testActiveCheckboxList(): void
     {
         $model = new HtmlTestModel();
 
@@ -2165,7 +2169,7 @@ HTML;
         $this->assertEqualsWithoutLE($expected, $actual);
     }
 
-    public function testActiveCheckboxList_options()
+    public function testActiveCheckboxList_options(): void
     {
         $model = new HtmlTestModel();
 
@@ -2176,7 +2180,7 @@ HTML;
         $this->assertEqualsWithoutLE($expected, $actual);
     }
 
-    public function testActiveTextInput_placeholderFillFromModel()
+    public function testActiveTextInput_placeholderFillFromModel(): void
     {
         $model = new HtmlTestModel();
 
@@ -2185,7 +2189,7 @@ HTML;
         $this->assertStringContainsString('placeholder="Name"', $html);
     }
 
-    public function testActiveTextInput_customPlaceholder()
+    public function testActiveTextInput_customPlaceholder(): void
     {
         $model = new HtmlTestModel();
 
@@ -2194,7 +2198,7 @@ HTML;
         $this->assertStringContainsString('placeholder="Custom placeholder"', $html);
     }
 
-    public function testActiveTextInput_placeholderFillFromModelTabular()
+    public function testActiveTextInput_placeholderFillFromModelTabular(): void
     {
         $model = new HtmlTestModel();
 
@@ -2203,7 +2207,7 @@ HTML;
         $this->assertStringContainsString('placeholder="Name"', $html);
     }
 
-    public function testOverrideSetActivePlaceholder()
+    public function testOverrideSetActivePlaceholder(): void
     {
         $model = new HtmlTestModel();
 
@@ -2298,7 +2302,7 @@ HTML;
 class MyHtml extends Html
 {
     /**
-     * @param \yii\base\Model $model
+     * @param Model $model
      * @param string $attribute
      * @param array $options
      */
@@ -2320,7 +2324,7 @@ class MyHtml extends Html
  */
 class HtmlTestModel extends DynamicModel
 {
-    public function init()
+    public function init(): void
     {
         foreach (['name', 'title', 'alias', 'types', 'description', 'radio', 'checkbox'] as $attribute) {
             $this->defineAttribute($attribute);
diff --git a/tests/framework/helpers/InflectorTest.php b/tests/framework/helpers/InflectorTest.php
index 5e442d600a..0561416ecc 100644
--- a/tests/framework/helpers/InflectorTest.php
+++ b/tests/framework/helpers/InflectorTest.php
@@ -24,7 +24,7 @@ class InflectorTest extends TestCase
         $this->destroyApplication();
     }
 
-    public function testPluralize()
+    public function testPluralize(): void
     {
         $testData = [
             'move' => 'moves',
@@ -55,7 +55,7 @@ class InflectorTest extends TestCase
         }
     }
 
-    public function testSingularize()
+    public function testSingularize(): void
     {
         $testData = [
             'moves' => 'move',
@@ -85,27 +85,27 @@ class InflectorTest extends TestCase
         }
     }
 
-    public function testTitleize()
+    public function testTitleize(): void
     {
         $this->assertEquals('Me my self and i', Inflector::titleize('MeMySelfAndI'));
         $this->assertEquals('Me My Self And I', Inflector::titleize('MeMySelfAndI', true));
         $this->assertEquals('Треба Більше Тестів!', Inflector::titleize('ТребаБільшеТестів!', true));
     }
 
-    public function testCamelize()
+    public function testCamelize(): void
     {
         $this->assertEquals('MeMySelfAndI', Inflector::camelize('me my_self-andI'));
         $this->assertEquals('QweQweEwq', Inflector::camelize('qwe qwe^ewq'));
         $this->assertEquals('ВідомоЩоТестиЗберігатьНашіНЕРВИ', Inflector::camelize('Відомо, що тести зберігать наші НЕРВИ! 🙃'));
     }
 
-    public function testUnderscore()
+    public function testUnderscore(): void
     {
         $this->assertEquals('me_my_self_and_i', Inflector::underscore('MeMySelfAndI'));
         $this->assertEquals('кожний_тест_особливий', Inflector::underscore('КожнийТестОсобливий'));
     }
 
-    public function testCamel2words()
+    public function testCamel2words(): void
     {
         $this->assertEquals('Camel Case', Inflector::camel2words('camelCase'));
         $this->assertEquals('Camel Case', Inflector::camel2words('CamelCase'));
@@ -124,7 +124,7 @@ class InflectorTest extends TestCase
         $this->assertEquals('Foo Bar', Inflector::camel2words('FOO BAR'));
     }
 
-    public function testCamel2id()
+    public function testCamel2id(): void
     {
         $this->assertEquals('post-tag', Inflector::camel2id('PostTag'));
         $this->assertEquals('post_tag', Inflector::camel2id('PostTag', '_'));
@@ -144,7 +144,7 @@ class InflectorTest extends TestCase
         $this->assertEquals('невже_і_це_працює', Inflector::camel2id('НевжеІЦеПрацює', '_', true));
     }
 
-    public function testId2camel()
+    public function testId2camel(): void
     {
         $this->assertEquals('PostTag', Inflector::id2camel('post-tag'));
         $this->assertEquals('PostTag', Inflector::id2camel('post_tag', '_'));
@@ -160,25 +160,25 @@ class InflectorTest extends TestCase
         $this->assertEquals('FooYBar', Inflector::id2camel('foo_y_bar', '_'));
     }
 
-    public function testHumanize()
+    public function testHumanize(): void
     {
         $this->assertEquals('Me my self and i', Inflector::humanize('me_my_self_and_i'));
         $this->assertEquals('Me My Self And I', Inflector::humanize('me_my_self_and_i', true));
         $this->assertEquals('Але й веселі ці ваші тести', Inflector::humanize('але_й_веселі_ці_ваші_тести'));
     }
 
-    public function testVariablize()
+    public function testVariablize(): void
     {
         $this->assertEquals('customerTable', Inflector::variablize('customer_table'));
         $this->assertEquals('ひらがなHepimiz', Inflector::variablize('ひらがな_hepimiz'));
     }
 
-    public function testTableize()
+    public function testTableize(): void
     {
         $this->assertEquals('customer_tables', Inflector::tableize('customerTable'));
     }
 
-    public function testSlugCommons()
+    public function testSlugCommons(): void
     {
         $data = [
             '' => '',
@@ -199,7 +199,7 @@ class InflectorTest extends TestCase
         }
     }
 
-    public function testSlugReplacements()
+    public function testSlugReplacements(): void
     {
         $this->assertEquals('dont_replace_replacement', Inflector::slug('dont replace_replacement', '_'));
         $this->assertEquals('remove_trailing_replacements', Inflector::slug('_remove trailing replacements_', '_'));
@@ -209,7 +209,7 @@ class InflectorTest extends TestCase
         $this->assertEquals('testtext', Inflector::slug('test text', ''));
     }
 
-    public function testSlugIntl()
+    public function testSlugIntl(): void
     {
         if (!extension_loaded('intl')) {
             $this->markTestSkipped('intl extension is required.');
@@ -244,7 +244,7 @@ class InflectorTest extends TestCase
         }
     }
 
-    public function testTransliterateStrict()
+    public function testTransliterateStrict(): void
     {
         if (!extension_loaded('intl')) {
             $this->markTestSkipped('intl extension is required.');
@@ -287,7 +287,7 @@ class InflectorTest extends TestCase
         }
     }
 
-    public function testTransliterateMedium()
+    public function testTransliterateMedium(): void
     {
         if (!extension_loaded('intl')) {
             $this->markTestSkipped('intl extension is required.');
@@ -330,7 +330,7 @@ class InflectorTest extends TestCase
         }
     }
 
-    public function testTransliterateLoose()
+    public function testTransliterateLoose(): void
     {
         if (!extension_loaded('intl')) {
             $this->markTestSkipped('intl extension is required.');
@@ -373,7 +373,7 @@ class InflectorTest extends TestCase
         }
     }
 
-    public function testSlugPhp()
+    public function testSlugPhp(): void
     {
         $data = [
             'we have недвижимость' => 'we-have',
@@ -384,12 +384,12 @@ class InflectorTest extends TestCase
         }
     }
 
-    public function testClassify()
+    public function testClassify(): void
     {
         $this->assertEquals('CustomerTable', Inflector::classify('customer_tables'));
     }
 
-    public function testOrdinalize()
+    public function testOrdinalize(): void
     {
         $this->assertEquals('21st', Inflector::ordinalize('21'));
         $this->assertEquals('22nd', Inflector::ordinalize('22'));
@@ -400,7 +400,7 @@ class InflectorTest extends TestCase
         $this->assertEquals('113th', Inflector::ordinalize('113'));
     }
 
-    public function testSentence()
+    public function testSentence(): void
     {
         $array = [];
         $this->assertEquals('', Inflector::sentence($array));
diff --git a/tests/framework/helpers/IpHelperTest.php b/tests/framework/helpers/IpHelperTest.php
index fb6b1e4037..6cf57edf61 100644
--- a/tests/framework/helpers/IpHelperTest.php
+++ b/tests/framework/helpers/IpHelperTest.php
@@ -2,6 +2,7 @@
 
 namespace yiiunit\framework\helpers;
 
+use Exception;
 use yii\helpers\IpHelper;
 use yiiunit\TestCase;
 
@@ -17,7 +18,7 @@ class IpHelperTest extends TestCase
      * @param $value
      * @param $expected
      */
-    public function testGetIpVersion($value, $expected, $message = '')
+    public function testGetIpVersion($value, $expected, $message = ''): void
     {
         $version = IpHelper::getIpVersion($value);
         $this->assertSame($expected, $version, $message);
@@ -37,7 +38,7 @@ class IpHelperTest extends TestCase
     /**
      * @dataProvider expandIpv6Provider
      */
-    public function testExpandIpv6($value, $expected, $message = '')
+    public function testExpandIpv6($value, $expected, $message = ''): void
     {
         $expanded = IpHelper::expandIPv6($value);
         $this->assertSame($expected, $expanded, $message);
@@ -51,12 +52,12 @@ class IpHelperTest extends TestCase
         ];
     }
 
-    public function testIpv6ExpandingWithInvalidValue()
+    public function testIpv6ExpandingWithInvalidValue(): void
     {
         try {
             IpHelper::expandIPv6('fa01::1/64');
             $this->assertTrue(true);
-        } catch (\Exception $exception) {
+        } catch (Exception $exception) {
             $this->assertStringEndsWith('Unrecognized address fa01::1/64', $exception->getMessage());
         }
     }
@@ -68,7 +69,7 @@ class IpHelperTest extends TestCase
      *
      * @dataProvider ip2binProvider
      */
-    public function testIp2bin($value, $expected, $message = '')
+    public function testIp2bin($value, $expected, $message = ''): void
     {
         $result = IpHelper::ip2bin($value);
         $this->assertSame($expected, $result, $message);
@@ -92,7 +93,7 @@ class IpHelperTest extends TestCase
      *
      * @dataProvider inRangeProvider
      */
-    public function testInRange($value, $range, $expected)
+    public function testInRange($value, $range, $expected): void
     {
         $result = IpHelper::inRange($value, $range);
         $this->assertSame($expected, $result);
diff --git a/tests/framework/helpers/JsonTest.php b/tests/framework/helpers/JsonTest.php
index f485fba465..c6b3b29705 100644
--- a/tests/framework/helpers/JsonTest.php
+++ b/tests/framework/helpers/JsonTest.php
@@ -8,6 +8,11 @@
 
 namespace yiiunit\framework\helpers;
 
+use stdClass;
+use SplStack;
+use yii\base\InvalidArgumentException;
+use DateTime;
+use DateTimeZone;
 use yii\helpers\Json;
 use yii\web\JsExpression;
 use yiiunit\framework\web\Post;
@@ -28,7 +33,7 @@ class JsonTest extends TestCase
         $this->destroyApplication();
     }
 
-    public function testEncode()
+    public function testEncode(): void
     {
         // Arrayable data encoding
         $dataArrayable = $this->getMockBuilder('\yii\base\Arrayable')->getMock();
@@ -65,7 +70,7 @@ class JsonTest extends TestCase
         // empty data encoding
         $data = [];
         $this->assertSame('[]', Json::encode($data));
-        $data = new \stdClass();
+        $data = new stdClass();
         $this->assertSame('{}', Json::encode($data));
 
         // expression encoding
@@ -111,7 +116,7 @@ PHP
         }
     }
 
-    public function testHtmlEncode()
+    public function testHtmlEncode(): void
     {
         // HTML escaped chars
         $data = '&<>"\'/';
@@ -177,14 +182,14 @@ PHP
         $document = simplexml_load_string($xml);
         $this->assertSame('{"child1":{},"child2":{"subElement":"sub"}}', Json::encode($document));
 
-        $postsStack = new \SplStack();
+        $postsStack = new SplStack();
         $postsStack->push(new Post(915, 'record1'));
         $postsStack->push(new Post(456, 'record2'));
 
         $this->assertSame('{"1":{"id":456,"title":"record2"},"0":{"id":915,"title":"record1"}}', Json::encode($postsStack));
     }
 
-    public function testDecode()
+    public function testDecode(): void
     {
         // empty value
         $json = '';
@@ -208,9 +213,9 @@ PHP
     /**
      * @covers ::decode
      */
-    public function testDecodeInvalidArgumentException()
+    public function testDecodeInvalidArgumentException(): void
     {
-        $this->expectException(\yii\base\InvalidArgumentException::class);
+        $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Invalid JSON data.');
 
         Json::decode([]);
@@ -219,13 +224,13 @@ PHP
     /**
      * @covers ::decode
      */
-    public function testHandleJsonError()
+    public function testHandleJsonError(): void
     {
         // basic syntax error
         try {
             $json = "{'a': '1'}";
             Json::decode($json);
-        } catch (\yii\base\InvalidArgumentException $e) {
+        } catch (InvalidArgumentException $e) {
             $this->assertSame(Json::$jsonErrorMessages['JSON_ERROR_SYNTAX'], $e->getMessage());
         }
 
@@ -235,7 +240,7 @@ PHP
             $data = ['a' => $fp];
             Json::encode($data);
             fclose($fp);
-        } catch (\yii\base\InvalidArgumentException $e) {
+        } catch (InvalidArgumentException $e) {
             if (PHP_VERSION_ID >= 50500) {
                 $this->assertSame(Json::$jsonErrorMessages['JSON_ERROR_UNSUPPORTED_TYPE'], $e->getMessage());
             } else {
@@ -244,7 +249,7 @@ PHP
         }
     }
 
-    public function testErrorSummary()
+    public function testErrorSummary(): void
     {
         $model = new JsonModel();
         $model->name = 'not_an_integer';
@@ -260,9 +265,9 @@ PHP
      * @see https://github.com/yiisoft/yii2/issues/17760
      * @covers ::encode
      */
-    public function testEncodeDateTime()
+    public function testEncodeDateTime(): void
     {
-        $input = new \DateTime('October 12, 2014', new \DateTimeZone('UTC'));
+        $input = new DateTime('October 12, 2014', new DateTimeZone('UTC'));
         $output = Json::encode($input);
         $this->assertEquals('{"date":"2014-10-12 00:00:00.000000","timezone_type":3,"timezone":"UTC"}', $output);
     }
@@ -270,7 +275,7 @@ PHP
     /**
      * @covers ::encode
      */
-    public function testPrettyPrint()
+    public function testPrettyPrint(): void
     {
         $defaultValue = Json::$prettyPrint;
         $input = ['a' => 1, 'b' => 2];
diff --git a/tests/framework/helpers/MarkdownTest.php b/tests/framework/helpers/MarkdownTest.php
index 39e7142897..def8d70c2c 100644
--- a/tests/framework/helpers/MarkdownTest.php
+++ b/tests/framework/helpers/MarkdownTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\helpers;
 
+use yii\base\InvalidArgumentException;
 use yii\helpers\Markdown;
 use yiiunit\TestCase;
 
@@ -27,7 +28,7 @@ class MarkdownTest extends TestCase
         $this->destroyApplication();
     }
 
-    public function testOriginalFlavor()
+    public function testOriginalFlavor(): void
     {
         $text = <<<'TEXT'
 html
@@ -44,15 +45,15 @@ TEXT;
         $this->assertEquals(Markdown::process($text), Markdown::process($text, 'gfm-comment'));
     }
 
-    public function testProcessInvalidArgumentException()
+    public function testProcessInvalidArgumentException(): void
     {
-        $this->expectException(\yii\base\InvalidArgumentException::class);
+        $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage("Markdown flavor 'undefined' is not defined.");
 
         Markdown::process('foo', 'undefined');
     }
 
-    public function testProcessParagraph()
+    public function testProcessParagraph(): void
     {
         $actual = Markdown::processParagraph('foo');
         $expected = 'foo';
diff --git a/tests/framework/helpers/ReplaceArrayValueTest.php b/tests/framework/helpers/ReplaceArrayValueTest.php
index b7d51233ea..e57a403bde 100644
--- a/tests/framework/helpers/ReplaceArrayValueTest.php
+++ b/tests/framework/helpers/ReplaceArrayValueTest.php
@@ -16,7 +16,7 @@ use yiiunit\TestCase;
  */
 class ReplaceArrayValueTest extends TestCase
 {
-    public function testSetStateWithoutValue()
+    public function testSetStateWithoutValue(): void
     {
         $this->expectException('yii\base\InvalidConfigException');
         $this->expectExceptionMessage('Failed to instantiate class "ReplaceArrayValue". Required parameter "value" is missing');
@@ -24,7 +24,7 @@ class ReplaceArrayValueTest extends TestCase
         $object::__set_state([]);
     }
 
-    public function testSetStateWithValue()
+    public function testSetStateWithValue(): void
     {
         $object = new ReplaceArrayValue('test');
         $result = $object::__set_state(['value' => 'test2']);
diff --git a/tests/framework/helpers/StringHelperTest.php b/tests/framework/helpers/StringHelperTest.php
index 603f4a9922..3d4ae65a16 100644
--- a/tests/framework/helpers/StringHelperTest.php
+++ b/tests/framework/helpers/StringHelperTest.php
@@ -25,13 +25,13 @@ class StringHelperTest extends TestCase
         $this->destroyApplication();
     }
 
-    public function testStrlen()
+    public function testStrlen(): void
     {
         $this->assertEquals(4, StringHelper::byteLength('this'));
         $this->assertEquals(6, StringHelper::byteLength('это'));
     }
 
-    public function testSubstr()
+    public function testSubstr(): void
     {
         $this->assertEquals('th', StringHelper::byteSubstr('this', 0, 2));
         $this->assertEquals('э', StringHelper::byteSubstr('это', 0, 2));
@@ -65,7 +65,7 @@ class StringHelperTest extends TestCase
         $this->assertEquals('', StringHelper::byteSubstr('это', -4, 0));
     }
 
-    public function testBasename()
+    public function testBasename(): void
     {
         $this->assertEquals('', StringHelper::basename(''));
 
@@ -109,7 +109,7 @@ class StringHelperTest extends TestCase
         $this->assertEquals('foo', StringHelper::basename('\\bar\\foo\\'));
     }
 
-    public function testTruncate()
+    public function testTruncate(): void
     {
         $this->assertEquals('привет, я multibyte...', StringHelper::truncate('привет, я multibyte строка!', 20));
         $this->assertEquals('Не трогаем строку', StringHelper::truncate('Не трогаем строку', 20));
@@ -130,7 +130,7 @@ class StringHelperTest extends TestCase
         $this->assertEquals('<div><ul><li>bullet1</li><li><div>b</div></li></ul></div>...', StringHelper::truncate('<div><ul><li>bullet1</li><li><div>bullet2</div></li></ul><br></div>', 8, '...', null, true));
     }
 
-    public function testTruncateWords()
+    public function testTruncateWords(): void
     {
         $this->assertEquals('это тестовая multibyte строка', StringHelper::truncateWords('это тестовая multibyte строка', 5));
         $this->assertEquals('это тестовая multibyte...', StringHelper::truncateWords('это тестовая multibyte строка', 3));
@@ -156,7 +156,7 @@ class StringHelperTest extends TestCase
      * @param string $string
      * @param string|null $with
      */
-    public function testStartsWith($result, $string, $with)
+    public function testStartsWith($result, $string, $with): void
     {
         // case sensitive version check
         $this->assertSame($result, StringHelper::startsWith($string, $with));
@@ -192,13 +192,13 @@ class StringHelperTest extends TestCase
         ];
     }
 
-    public function testStartsWithCaseSensitive()
+    public function testStartsWithCaseSensitive(): void
     {
         $this->assertFalse(StringHelper::startsWith('Abc', 'a'));
         $this->assertFalse(StringHelper::startsWith('üЯ multibyte', 'Üя multibyte'));
     }
 
-    public function testStartsWithCaseInsensitive()
+    public function testStartsWithCaseInsensitive(): void
     {
         $this->assertTrue(StringHelper::startsWith('sTrInG', 'StRiNg', false));
         $this->assertTrue(StringHelper::startsWith('CaSe', 'cAs', false));
@@ -212,7 +212,7 @@ class StringHelperTest extends TestCase
      * @param string $string
      * @param string|null $with
      */
-    public function testEndsWith($result, $string, $with)
+    public function testEndsWith($result, $string, $with): void
     {
         // case sensitive version check
         $this->assertSame($result, StringHelper::endsWith($string, $with));
@@ -248,20 +248,20 @@ class StringHelperTest extends TestCase
         ];
     }
 
-    public function testEndsWithCaseSensitive()
+    public function testEndsWithCaseSensitive(): void
     {
         $this->assertFalse(StringHelper::endsWith('string', 'G'));
         $this->assertFalse(StringHelper::endsWith('multibyte строка', 'А'));
     }
 
-    public function testEndsWithCaseInsensitive()
+    public function testEndsWithCaseInsensitive(): void
     {
         $this->assertTrue(StringHelper::endsWith('sTrInG', 'StRiNg', false));
         $this->assertTrue(StringHelper::endsWith('string', 'nG', false));
         $this->assertTrue(StringHelper::endsWith('BüЯйΨ', 'ÜяЙΨ', false));
     }
 
-    public function testExplode()
+    public function testExplode(): void
     {
         $this->assertEquals(['It', 'is', 'a first', 'test'], StringHelper::explode('It, is, a first, test'));
         $this->assertEquals(['It', 'is', 'a test with trimmed digits', '0', '1', '2'], StringHelper::explode('It, is, a test with trimmed digits, 0, 1, 2', ',', true, true));
@@ -276,7 +276,7 @@ class StringHelperTest extends TestCase
         }));
     }
 
-    public function testWordCount()
+    public function testWordCount(): void
     {
         $this->assertEquals(3, StringHelper::countWords('china 中国 ㄍㄐㄋㄎㄌ'));
         $this->assertEquals(4, StringHelper::countWords('и много тут слов?'));
@@ -290,7 +290,7 @@ class StringHelperTest extends TestCase
      * @param $input
      * @param $base64UrlEncoded
      */
-    public function testBase64UrlEncode($input, $base64UrlEncoded)
+    public function testBase64UrlEncode($input, $base64UrlEncoded): void
     {
         $encoded = StringHelper::base64UrlEncode($input);
         $this->assertEquals($base64UrlEncoded, $encoded);
@@ -301,7 +301,7 @@ class StringHelperTest extends TestCase
      * @param $output
      * @param $base64UrlEncoded
      */
-    public function testBase64UrlDecode($output, $base64UrlEncoded)
+    public function testBase64UrlDecode($output, $base64UrlEncoded): void
     {
         $decoded = StringHelper::base64UrlDecode($base64UrlEncoded);
         $this->assertEquals($output, $decoded);
@@ -399,7 +399,7 @@ class StringHelperTest extends TestCase
      * @param bool $expectedResult
      * @param array $options
      */
-    public function testMatchWildcard($pattern, $string, $expectedResult, $options = [])
+    public function testMatchWildcard($pattern, $string, $expectedResult, $options = []): void
     {
         $this->assertSame($expectedResult, StringHelper::matchWildcard($pattern, $string, $options));
     }
@@ -421,7 +421,7 @@ class StringHelperTest extends TestCase
      * @param string $expectedResult
      * @dataProvider dataProviderMb_ucfirst
      */
-    public function testMb_ucfirst($string, $expectedResult)
+    public function testMb_ucfirst($string, $expectedResult): void
     {
         $this->assertSame($expectedResult, StringHelper::mb_ucfirst($string));
     }
@@ -450,7 +450,7 @@ class StringHelperTest extends TestCase
      * @param string $expectedResult
      * @dataProvider dataProviderMb_ucwords
      */
-    public function testMb_ucwords($string, $expectedResult)
+    public function testMb_ucwords($string, $expectedResult): void
     {
         $this->assertSame($expectedResult, StringHelper::mb_ucwords($string));
     }
@@ -460,7 +460,7 @@ class StringHelperTest extends TestCase
      * @param string $expectedResult
      * @dataProvider dataProviderDirname
      */
-    public function testDirname($string, $expectedResult)
+    public function testDirname($string, $expectedResult): void
     {
         $this->assertSame($expectedResult, StringHelper::dirname($string));
     }
@@ -477,7 +477,7 @@ class StringHelperTest extends TestCase
         ];
     }
 
-    public function testMask()
+    public function testMask(): void
     {
         // Standard masking
         $this->assertSame('12******90', StringHelper::mask('1234567890', 2, 6));
@@ -516,7 +516,7 @@ class StringHelperTest extends TestCase
      * @param string $expectedResult
      * @dataProvider dataProviderFindBetween
      */
-    public function testFindBetween($string, $start, $end, $expectedResult)
+    public function testFindBetween($string, $start, $end, $expectedResult): void
     {
         $this->assertSame($expectedResult, StringHelper::findBetween($string, $start, $end));
     }
diff --git a/tests/framework/helpers/UnsetArrayValueTest.php b/tests/framework/helpers/UnsetArrayValueTest.php
index 032f62869c..1421f05b8d 100644
--- a/tests/framework/helpers/UnsetArrayValueTest.php
+++ b/tests/framework/helpers/UnsetArrayValueTest.php
@@ -16,7 +16,7 @@ use yiiunit\TestCase;
  */
 class UnsetArrayValueTest extends TestCase
 {
-    public function testSetState()
+    public function testSetState(): void
     {
         $object = new UnsetArrayValue();
         $result = $object::__set_state([]);
diff --git a/tests/framework/helpers/UrlTest.php b/tests/framework/helpers/UrlTest.php
index c97cc8736f..85353e262f 100644
--- a/tests/framework/helpers/UrlTest.php
+++ b/tests/framework/helpers/UrlTest.php
@@ -64,7 +64,7 @@ class UrlTest extends TestCase
      */
     protected function mockAction($controllerId, $actionID, $moduleID = null, $params = [])
     {
-        \Yii::$app->controller = $controller = new Controller($controllerId, \Yii::$app);
+        Yii::$app->controller = $controller = new Controller($controllerId, Yii::$app);
         $controller->actionParams = $params;
         $controller->action = new Action($actionID, $controller);
 
@@ -75,10 +75,10 @@ class UrlTest extends TestCase
 
     protected function removeMockedAction()
     {
-        \Yii::$app->controller = null;
+        Yii::$app->controller = null;
     }
 
-    public function testToRoute()
+    public function testToRoute(): void
     {
         $this->mockAction('page', 'view', null, ['id' => 10]);
 
@@ -108,9 +108,9 @@ class UrlTest extends TestCase
         $this->assertEquals('//example.com/base/index.php?r=stats%2Fuser%2Fview&id=42', Url::toRoute(['user/view', 'id' => 42], ''));
 
         // alias support
-        \Yii::setAlias('@userView', 'user/view');
+        Yii::setAlias('@userView', 'user/view');
         $this->assertEquals('/base/index.php?r=stats%2Fuser%2Fview', Url::toRoute('@userView'));
-        \Yii::setAlias('@userView', null);
+        Yii::setAlias('@userView', null);
 
         // In case there is no controller, an exception should be thrown for relative route
         $this->removeMockedAction();
@@ -119,7 +119,7 @@ class UrlTest extends TestCase
         Url::toRoute('site/view');
     }
 
-    public function testCurrent()
+    public function testCurrent(): void
     {
         $this->mockAction('page', 'view', null, []);
         Yii::$app->request->setQueryParams(['id' => 10, 'name' => 'test', 10 => 0]);
@@ -142,7 +142,7 @@ class UrlTest extends TestCase
         $this->assertEquals($uri . '&arr%5Battr_one%5D=1&arr%5Battr_two%5D=two', Url::current(['arr' => ['attr_two' => 'two']]));
     }
 
-    public function testPrevious()
+    public function testPrevious(): void
     {
         Yii::$app->getUser()->login(UserIdentity::findIdentity('user1'));
 
@@ -153,7 +153,7 @@ class UrlTest extends TestCase
         $this->assertEquals('/base/index.php', Url::previous());
     }
 
-    public function testTo()
+    public function testTo(): void
     {
         // is an array: the first array element is considered a route, while the rest of the name-value
         // pairs are treated as the parameters to be used for URL creation using Url::toRoute.
@@ -163,9 +163,9 @@ class UrlTest extends TestCase
         $this->assertEquals('/base/index.php?r=page%2Fview', Url::to(['']));
 
         // alias support
-        \Yii::setAlias('@pageEdit', 'edit');
+        Yii::setAlias('@pageEdit', 'edit');
         $this->assertEquals('/base/index.php?r=page%2Fedit&id=20', Url::to(['@pageEdit', 'id' => 20]));
-        \Yii::setAlias('@pageEdit', null);
+        Yii::setAlias('@pageEdit', null);
 
         $this->assertEquals('http://example.com/base/index.php?r=page%2Fedit&id=20', Url::to(['edit', 'id' => 20], true));
         $this->assertEquals('http://example.com/base/index.php?r=page%2Fedit', Url::to(['edit'], true));
@@ -184,11 +184,11 @@ class UrlTest extends TestCase
         // is a non-empty string: it will first be processed by [[Yii::getAlias()]]. If the result
         // is an absolute URL, it will be returned either without any change or, if schema was specified, with schema
         // replaced; Otherwise, the result will be prefixed with [[\yii\web\Request::baseUrl]] and returned.
-        \Yii::setAlias('@web1', 'http://test.example.com/test/me1');
-        \Yii::setAlias('@web2', 'test/me2');
-        \Yii::setAlias('@web3', '');
-        \Yii::setAlias('@web4', '/test');
-        \Yii::setAlias('@web5', '#test');
+        Yii::setAlias('@web1', 'http://test.example.com/test/me1');
+        Yii::setAlias('@web2', 'test/me2');
+        Yii::setAlias('@web3', '');
+        Yii::setAlias('@web4', '/test');
+        Yii::setAlias('@web5', '#test');
 
         $this->assertEquals('test/me1', Url::to('test/me1'));
         $this->assertEquals('javascript:test/me1', Url::to('javascript:test/me1'));
@@ -226,11 +226,11 @@ class UrlTest extends TestCase
         $this->assertEquals('//example.com/#test', Url::to('@web5', ''));
 
         // @see https://github.com/yiisoft/yii2/issues/13156
-        \Yii::setAlias('@cdn', '//cdn.example.com');
+        Yii::setAlias('@cdn', '//cdn.example.com');
         $this->assertEquals('http://cdn.example.com/images/logo.gif', Url::to('@cdn/images/logo.gif', 'http'));
         $this->assertEquals('//cdn.example.com/images/logo.gif', Url::to('@cdn/images/logo.gif', ''));
         $this->assertEquals('https://cdn.example.com/images/logo.gif', Url::to('@cdn/images/logo.gif', 'https'));
-        \Yii::setAlias('@cdn', null);
+        Yii::setAlias('@cdn', null);
 
         //In case there is no controller, throw an exception
         $this->removeMockedAction();
@@ -242,7 +242,7 @@ class UrlTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/11925
      */
-    public function testToWithSuffix()
+    public function testToWithSuffix(): void
     {
         Yii::$app->set('urlManager', [
             'class' => 'yii\web\UrlManager',
@@ -272,7 +272,7 @@ class UrlTest extends TestCase
         $this->assertMatchesRegularExpression('~<a href="/site/page.html\?view=about">~', $output);
     }
 
-    public function testBase()
+    public function testBase(): void
     {
         $this->mockAction('page', 'view', null, ['id' => 10]);
         $this->assertEquals('/base', Url::base());
@@ -281,7 +281,7 @@ class UrlTest extends TestCase
         $this->assertEquals('//example.com/base', Url::base(''));
     }
 
-    public function testHome()
+    public function testHome(): void
     {
         $this->assertEquals('/base/index.php', Url::home());
         $this->assertEquals('http://example.com/base/index.php', Url::home(true));
@@ -289,14 +289,14 @@ class UrlTest extends TestCase
         $this->assertEquals('//example.com/base/index.php', Url::home(''));
     }
 
-    public function testCanonical()
+    public function testCanonical(): void
     {
         $this->mockAction('page', 'view', null, ['id' => 10]);
         $this->assertEquals('http://example.com/base/index.php?r=page%2Fview&id=10', Url::canonical());
         $this->removeMockedAction();
     }
 
-    public function testIsRelative()
+    public function testIsRelative(): void
     {
         $this->assertTrue(Url::isRelative('/test/index.php'));
         $this->assertTrue(Url::isRelative('index.php'));
@@ -305,7 +305,7 @@ class UrlTest extends TestCase
         $this->assertFalse(Url::isRelative('https://example.com/'));
     }
 
-    public function testRemember()
+    public function testRemember(): void
     {
         Yii::$app->getUser()->login(UserIdentity::findIdentity('user1'));
 
diff --git a/tests/framework/helpers/VarDumperTest.php b/tests/framework/helpers/VarDumperTest.php
index bf9e130375..550455f993 100644
--- a/tests/framework/helpers/VarDumperTest.php
+++ b/tests/framework/helpers/VarDumperTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\helpers;
 
+use StdClass;
 use yii\helpers\VarDumper;
 use yiiunit\data\helpers\CustomDebugInfo;
 use yiiunit\TestCase;
@@ -25,7 +26,7 @@ class VarDumperTest extends TestCase
         $this->destroyApplication();
     }
 
-    public function testDumpIncompleteObject()
+    public function testDumpIncompleteObject(): void
     {
         $serializedObj = 'O:16:"nonExistingClass":0:{}';
         $incompleteObj = unserialize($serializedObj);
@@ -34,7 +35,7 @@ class VarDumperTest extends TestCase
         $this->assertStringContainsString('nonExistingClass', $dumpResult);
     }
 
-    public function testExportIncompleteObject()
+    public function testExportIncompleteObject(): void
     {
         $serializedObj = 'O:16:"nonExistingClass":0:{}';
         $incompleteObj = unserialize($serializedObj);
@@ -42,12 +43,12 @@ class VarDumperTest extends TestCase
         $this->assertStringContainsString('nonExistingClass', $exportResult);
     }
 
-    public function testDumpObject()
+    public function testDumpObject(): void
     {
-        $obj = new \StdClass();
+        $obj = new StdClass();
         $this->assertEquals("stdClass#1\n(\n)", VarDumper::dumpAsString($obj));
 
-        $obj = new \StdClass();
+        $obj = new StdClass();
         $obj->name = 'test-name';
         $obj->price = 19;
         $dumpResult = VarDumper::dumpAsString($obj);
@@ -143,7 +144,7 @@ RESULT;
 
         // Objects :
 
-        $var = new \StdClass();
+        $var = new StdClass();
         $var->testField = 'Test Value';
         $expectedResult = "unserialize('" . serialize($var) . "')";
         $data[] = [$var, $expectedResult];
@@ -167,7 +168,7 @@ RESULT;
      * @param mixed $var
      * @param string $expectedResult
      */
-    public function testExport($var, $expectedResult)
+    public function testExport($var, $expectedResult): void
     {
         $exportResult = VarDumper::export($var);
         $this->assertEqualsWithoutLE($expectedResult, $exportResult);
@@ -177,17 +178,17 @@ RESULT;
     /**
      * @depends testExport
      */
-    public function testExportObjectFallback()
+    public function testExportObjectFallback(): void
     {
-        $var = new \StdClass();
+        $var = new StdClass();
         $var->testFunction = function () {
             return 2;
         };
         $exportResult = VarDumper::export($var);
         $this->assertNotEmpty($exportResult);
 
-        $master = new \StdClass();
-        $slave = new \StdClass();
+        $master = new StdClass();
+        $slave = new StdClass();
         $master->slave = $slave;
         $slave->master = $master;
         $master->function = function () {
@@ -201,7 +202,7 @@ RESULT;
     /**
      * @depends testDumpObject
      */
-    public function testDumpClassWithCustomDebugInfo()
+    public function testDumpClassWithCustomDebugInfo(): void
     {
         $object = new CustomDebugInfo();
         $object->volume = 10;
diff --git a/tests/framework/i18n/DbMessageSourceTest.php b/tests/framework/i18n/DbMessageSourceTest.php
index 5c764f0797..4e0d091b1d 100644
--- a/tests/framework/i18n/DbMessageSourceTest.php
+++ b/tests/framework/i18n/DbMessageSourceTest.php
@@ -8,6 +8,11 @@
 
 namespace yiiunit\framework\i18n;
 
+use yii\console\Application;
+use yii\console\Controller;
+use yii\db\Exception;
+use yii\base\InvalidConfigException;
+use yii\base\InvalidParamException;
 use Yii;
 use yii\base\Event;
 use yii\db\Connection;
@@ -52,7 +57,7 @@ class DbMessageSourceTest extends I18NTest
     protected static function runConsoleAction($route, $params = [])
     {
         if (Yii::$app === null) {
-            new \yii\console\Application([
+            new Application([
                 'id' => 'Migrator',
                 'basePath' => '@yiiunit',
                 'controllerMap' => [
@@ -67,7 +72,7 @@ class DbMessageSourceTest extends I18NTest
         ob_start();
         $result = Yii::$app->runAction($route, $params);
         echo 'Result is ' . $result;
-        if ($result !== \yii\console\Controller::EXIT_CODE_NORMAL) {
+        if ($result !== Controller::EXIT_CODE_NORMAL) {
             ob_end_flush();
         } else {
             ob_end_clean();
@@ -116,10 +121,10 @@ class DbMessageSourceTest extends I18NTest
     }
 
     /**
-     * @return \yii\db\Connection
-     * @throws \yii\db\Exception
-     * @throws \yii\base\InvalidConfigException
-     * @throws \yii\base\InvalidParamException
+     * @return Connection
+     * @throws Exception
+     * @throws InvalidConfigException
+     * @throws InvalidParamException
      */
     public static function getConnection()
     {
@@ -142,7 +147,7 @@ class DbMessageSourceTest extends I18NTest
         return static::$db;
     }
 
-    public function testMissingTranslationEvent()
+    public function testMissingTranslationEvent(): void
     {
         $this->assertEquals('Hallo Welt!', $this->i18n->translate('test', 'Hello world!', [], 'de-DE'));
         $this->assertEquals('Missing translation message.', $this->i18n->translate('test', 'Missing translation message.', [], 'de-DE'));
@@ -168,7 +173,7 @@ class DbMessageSourceTest extends I18NTest
         Event::off(DbMessageSource::className(), DbMessageSource::EVENT_MISSING_TRANSLATION);
     }
 
-    public function testIssue11429($sourceLanguage = null)
+    public function testIssue11429($sourceLanguage = null): void
     {
         $this->markTestSkipped('DbMessageSource does not produce any errors when messages file is missing.');
     }
diff --git a/tests/framework/i18n/FallbackMessageFormatterTest.php b/tests/framework/i18n/FallbackMessageFormatterTest.php
index be5b21ee89..dd4d8d4199 100644
--- a/tests/framework/i18n/FallbackMessageFormatterTest.php
+++ b/tests/framework/i18n/FallbackMessageFormatterTest.php
@@ -183,14 +183,14 @@ _MSG_
      * @param string $expected
      * @param array $args
      */
-    public function testNamedArguments($pattern, $expected, $args)
+    public function testNamedArguments($pattern, $expected, $args): void
     {
         $formatter = new FallbackMessageFormatter();
         $result = $formatter->fallbackFormat($pattern, $args, 'en-US');
         $this->assertEquals($expected, $result, $formatter->getErrorMessage());
     }
 
-    public function testInsufficientArguments()
+    public function testInsufficientArguments(): void
     {
         $expected = '{' . self::SUBJECT . '} is ' . self::N_VALUE;
 
@@ -202,7 +202,7 @@ _MSG_
         $this->assertEquals($expected, $result);
     }
 
-    public function testNoParams()
+    public function testNoParams(): void
     {
         $pattern = '{' . self::SUBJECT . '} is ' . self::N;
 
@@ -211,7 +211,7 @@ _MSG_
         $this->assertEquals($pattern, $result, $formatter->getErrorMessage());
     }
 
-    public function testGridViewMessage()
+    public function testGridViewMessage(): void
     {
         $pattern = 'Showing <b>{begin, number}-{end, number}</b> of <b>{totalCount, number}</b> {totalCount, plural, one{item} other{items}}.';
         $formatter = new FallbackMessageFormatter();
@@ -219,7 +219,7 @@ _MSG_
         $this->assertEquals('Showing <b>1-5</b> of <b>10</b> items.', $result);
     }
 
-    public function testUnsupportedPercentException()
+    public function testUnsupportedPercentException(): void
     {
         $pattern = 'Number {' . self::N . ', number, percent}';
         $formatter = new FallbackMessageFormatter();
@@ -227,7 +227,7 @@ _MSG_
         $formatter->fallbackFormat($pattern, [self::N => self::N_VALUE], 'en-US');
     }
 
-    public function testUnsupportedCurrencyException()
+    public function testUnsupportedCurrencyException(): void
     {
         $pattern = 'Number {' . self::N . ', number, currency}';
         $formatter = new FallbackMessageFormatter();
diff --git a/tests/framework/i18n/FormatterDateTest.php b/tests/framework/i18n/FormatterDateTest.php
index 7cd067c032..7f4533eb02 100644
--- a/tests/framework/i18n/FormatterDateTest.php
+++ b/tests/framework/i18n/FormatterDateTest.php
@@ -8,6 +8,9 @@
 
 namespace yiiunit\framework\i18n;
 
+use DateTimeImmutable;
+use IntlDateFormatter;
+use DateTimeZone;
 use DateInterval;
 use DateTime;
 use yii\i18n\Formatter;
@@ -43,7 +46,7 @@ class FormatterDateTest extends TestCase
         $this->formatter = null;
     }
 
-    public function testFormat()
+    public function testFormat(): void
     {
         $value = time();
         $this->assertSame(date('M j, Y', $value), $this->formatter->format($value, 'date'));
@@ -53,12 +56,12 @@ class FormatterDateTest extends TestCase
         $this->assertSame(date('Y-m-d', $value), $this->formatter->format($value, 'data'));
     }
 
-    public function testIntlAsDate()
+    public function testIntlAsDate(): void
     {
         $this->testAsDate();
     }
 
-    public function testAsDate()
+    public function testAsDate(): void
     {
         $value = time();
         $this->assertSame(date('M j, Y', $value), $this->formatter->asDate($value));
@@ -75,7 +78,7 @@ class FormatterDateTest extends TestCase
         $this->assertSame(date('F j, Y', $value->getTimestamp()), $this->formatter->asDate($value, 'long'));
 
         if (PHP_VERSION_ID >= 50500) {
-            $value = new \DateTimeImmutable();
+            $value = new DateTimeImmutable();
             $this->assertSame(date('M j, Y', $value->getTimestamp()), $this->formatter->asDate($value));
             $this->assertSame(date('Y/m/d', $value->getTimestamp()), $this->formatter->asDate($value, 'php:Y/m/d'));
             $this->assertSame(date('m/d/Y', $value->getTimestamp()), $this->formatter->asDate($value, 'MM/dd/yyyy'));
@@ -92,11 +95,11 @@ class FormatterDateTest extends TestCase
         $this->assertSame($this->formatter->nullDisplay, $this->formatter->asDate(null));
     }
 
-    public function testIntlAsDateOtherCalendars()
+    public function testIntlAsDateOtherCalendars(): void
     {
         // Persian calendar
         $this->formatter->locale = 'fa_IR@calendar=persian';
-        $this->formatter->calendar = \IntlDateFormatter::TRADITIONAL;
+        $this->formatter->calendar = IntlDateFormatter::TRADITIONAL;
         $this->formatter->timeZone = 'UTC';
 
         $value = 1451606400; // Fri, 01 Jan 2016 00:00:00 (UTC)
@@ -107,13 +110,13 @@ class FormatterDateTest extends TestCase
         $this->assertSame('۱۳۹۴', $this->formatter->asDate($value, 'php:Y'));
 
         if (version_compare(PHP_VERSION, '5.5.0', '>=')) {
-            $value = new \DateTimeImmutable('2016-01-01 00:00:00', new \DateTimeZone('UTC'));
+            $value = new DateTimeImmutable('2016-01-01 00:00:00', new DateTimeZone('UTC'));
             $this->assertSame('۱۳۹۴', $this->formatter->asDate($value, 'php:Y'));
         }
 
         // Buddhist calendar
         $this->formatter->locale = 'fr_FR@calendar=buddhist';
-        $this->formatter->calendar = \IntlDateFormatter::TRADITIONAL;
+        $this->formatter->calendar = IntlDateFormatter::TRADITIONAL;
         $this->formatter->timeZone = 'UTC';
 
         $value = 1451606400; // Fri, 01 Jan 2016 00:00:00 (UTC)
@@ -124,12 +127,12 @@ class FormatterDateTest extends TestCase
         $this->assertSame('2559', $this->formatter->asDate($value, 'php:Y'));
 
         if (version_compare(PHP_VERSION, '5.5.0', '>=')) {
-            $value = new \DateTimeImmutable('2016-01-01 00:00:00', new \DateTimeZone('UTC'));
+            $value = new DateTimeImmutable('2016-01-01 00:00:00', new DateTimeZone('UTC'));
             $this->assertSame('2559', $this->formatter->asDate($value, 'php:Y'));
         }
     }
 
-    public function testIntlAsTime()
+    public function testIntlAsTime(): void
     {
         $this->testAsTime();
 
@@ -140,7 +143,7 @@ class FormatterDateTest extends TestCase
         $this->assertSame('00:00:00', $this->formatter->asTime(false));
     }
 
-    public function testAsTime()
+    public function testAsTime(): void
     {
         $value = time();
         $this->assertSameAnyWhitespace(date('g:i:s A', $value), $this->formatter->asTime($value));
@@ -151,7 +154,7 @@ class FormatterDateTest extends TestCase
         $this->assertSame(date('h:i:s A', $value->getTimestamp()), $this->formatter->asTime($value, 'php:h:i:s A'));
 
         if (version_compare(PHP_VERSION, '5.5.0', '>=')) {
-            $value = new \DateTimeImmutable();
+            $value = new DateTimeImmutable();
             $this->assertSameAnyWhitespace(date('g:i:s A', $value->getTimestamp()), $this->formatter->asTime($value));
             $this->assertSame(date('h:i:s A', $value->getTimestamp()), $this->formatter->asTime($value, 'php:h:i:s A'));
         }
@@ -164,7 +167,7 @@ class FormatterDateTest extends TestCase
         $this->assertSame($this->formatter->nullDisplay, $this->formatter->asTime(null));
     }
 
-    public function testIntlAsDatetime()
+    public function testIntlAsDatetime(): void
     {
         $this->testAsDatetime();
 
@@ -175,7 +178,7 @@ class FormatterDateTest extends TestCase
         $this->assertMatchesRegularExpression('~01\.01\.1970,? 00:00:00~', $this->formatter->asDatetime(false));
     }
 
-    public function testAsDatetime()
+    public function testAsDatetime(): void
     {
         $value = time();
         $this->assertMatchesRegularExpression(
@@ -202,7 +205,7 @@ class FormatterDateTest extends TestCase
         $this->assertSame(date('Y/m/d h:i:s A', $value->getTimestamp()), $this->formatter->asDatetime($date, 'php:Y/m/d h:i:s A'));
 
         if (PHP_VERSION_ID >= 50500) {
-            $value = new \DateTimeImmutable();
+            $value = new DateTimeImmutable();
             $this->assertMatchesRegularExpression(
                 $this->sanitizeWhitespaces(date('~M j, Y,? g:i:s A~', $value->getTimestamp())),
                 $this->sanitizeWhitespaces($this->formatter->asDatetime($value))
@@ -233,12 +236,12 @@ class FormatterDateTest extends TestCase
         $this->assertSame($this->formatter->nullDisplay, $this->formatter->asDatetime(null));
     }
 
-    public function testIntlAsTimestamp()
+    public function testIntlAsTimestamp(): void
     {
         $this->testAsTimestamp();
     }
 
-    public function testAsTimestamp()
+    public function testAsTimestamp(): void
     {
         $value = time();
         $this->assertSame("$value", $this->formatter->asTimestamp($value));
@@ -259,7 +262,7 @@ class FormatterDateTest extends TestCase
         $this->assertSame($this->formatter->nullDisplay, $this->formatter->asTimestamp(null));
     }
 
-    public function testIntlDateRangeLow()
+    public function testIntlDateRangeLow(): void
     {
         // intl does not support high date ranges on 32bit systems, the implementation uses a fallback to PHP formatter
         $this->testDateRangeLow();
@@ -269,7 +272,7 @@ class FormatterDateTest extends TestCase
      * Test for dates before 1970.
      * @see https://github.com/yiisoft/yii2/issues/3126
      */
-    public function testDateRangeLow()
+    public function testDateRangeLow(): void
     {
         // https://en.wikipedia.org/wiki/Year_2038_problem
         $this->assertSame('13-12-1901', $this->formatter->asDate('1901-12-13', 'dd-MM-yyyy'));
@@ -279,7 +282,7 @@ class FormatterDateTest extends TestCase
         $this->assertSame('14-01-1732', $this->formatter->asDate('1732-01-14', 'dd-MM-yyyy'));
     }
 
-    public function testIntlDateRangeHigh()
+    public function testIntlDateRangeHigh(): void
     {
         // intl does not support high date ranges on 32bit systems, the implementation uses a fallback to PHP formatter
         $this->testDateRangeHigh();
@@ -289,7 +292,7 @@ class FormatterDateTest extends TestCase
      * Test for dates after 2038.
      * @see https://github.com/yiisoft/yii2/issues/3126
      */
-    public function testDateRangeHigh()
+    public function testDateRangeHigh(): void
     {
         // https://en.wikipedia.org/wiki/Year_2038_problem
         $this->assertSame('19-01-2038', $this->formatter->asDate('2038-01-19', 'dd-MM-yyyy'));
@@ -310,12 +313,12 @@ class FormatterDateTest extends TestCase
         return $date;
     }
 
-    public function testIntlAsRelativeTime()
+    public function testIntlAsRelativeTime(): void
     {
         $this->testAsRelativeTime();
     }
 
-    public function testAsRelativeTime()
+    public function testAsRelativeTime(): void
     {
         $interval_1_second = new DateInterval('PT1S');
         $interval_244_seconds = new DateInterval('PT244S');
@@ -448,12 +451,12 @@ class FormatterDateTest extends TestCase
         $this->assertSame('a minute ago', $this->formatter->asRelativeTime($now));
     }
 
-    public function testIntlAsDuration()
+    public function testIntlAsDuration(): void
     {
         $this->testAsDuration();
     }
 
-    public function testAsDuration()
+    public function testAsDuration(): void
     {
         $interval_0_seconds = new DateInterval('PT0S');
         $interval_1_second = new DateInterval('PT1S');
@@ -560,7 +563,7 @@ class FormatterDateTest extends TestCase
      * @param mixed $value
      * @param mixed|null $expectedException
      */
-    public function testIntlDateInput($expected, $value, $expectedException = null)
+    public function testIntlDateInput($expected, $value, $expectedException = null): void
     {
         $this->testDateInput($expected, $value, $expectedException);
     }
@@ -571,7 +574,7 @@ class FormatterDateTest extends TestCase
      * @param mixed $value
      * @param mixed|null $expectedException
      */
-    public function testDateInput($expected, $value, $expectedException = null)
+    public function testDateInput($expected, $value, $expectedException = null): void
     {
         if ($expectedException !== null) {
             $this->expectException($expectedException);
@@ -598,8 +601,8 @@ class FormatterDateTest extends TestCase
      */
     public function provideTimesAndTz()
     {
-        $utc = new \DateTimeZone('UTC');
-        $berlin = new \DateTimeZone('Europe/Berlin');
+        $utc = new DateTimeZone('UTC');
+        $berlin = new DateTimeZone('Europe/Berlin');
         $result = [];
         foreach ($this->provideTimezones() as $tz) {
             $result[] = [$tz[0], 1407674460,                          1388580060];
@@ -615,8 +618,8 @@ class FormatterDateTest extends TestCase
             $result[] = [$tz[0], new DateTime('2014-08-10 12:41:00', $utc), new DateTime('2014-01-01 12:41:00', $utc)];
             $result[] = [$tz[0], new DateTime('2014-08-10 14:41:00', $berlin), new DateTime('2014-01-01 13:41:00', $berlin)];
             if (version_compare(PHP_VERSION, '5.5.0', '>=')) {
-                $result[] = [$tz[0], new \DateTimeImmutable('2014-08-10 12:41:00', $utc), new \DateTimeImmutable('2014-01-01 12:41:00', $utc)];
-                $result[] = [$tz[0], new \DateTimeImmutable('2014-08-10 14:41:00', $berlin), new \DateTimeImmutable('2014-01-01 13:41:00', $berlin)];
+                $result[] = [$tz[0], new DateTimeImmutable('2014-08-10 12:41:00', $utc), new DateTimeImmutable('2014-01-01 12:41:00', $utc)];
+                $result[] = [$tz[0], new DateTimeImmutable('2014-08-10 14:41:00', $berlin), new DateTimeImmutable('2014-01-01 13:41:00', $berlin)];
             }
         }
 
@@ -630,7 +633,7 @@ class FormatterDateTest extends TestCase
      * @param mixed $inputTimeDst
      * @param mixed $inputTimeNonDst
      */
-    public function testIntlTimezoneInput($defaultTz, $inputTimeDst, $inputTimeNonDst)
+    public function testIntlTimezoneInput($defaultTz, $inputTimeDst, $inputTimeNonDst): void
     {
         $this->testTimezoneInput($defaultTz, $inputTimeDst, $inputTimeNonDst);
     }
@@ -642,7 +645,7 @@ class FormatterDateTest extends TestCase
      * @param mixed $inputTimeDst
      * @param mixed $inputTimeNonDst
      */
-    public function testTimezoneInput($defaultTz, $inputTimeDst, $inputTimeNonDst)
+    public function testTimezoneInput($defaultTz, $inputTimeDst, $inputTimeNonDst): void
     {
         date_default_timezone_set($defaultTz); // formatting has to be independent of the default timezone set by PHP
         $this->formatter->datetimeFormat = 'yyyy-MM-dd HH:mm:ss';
@@ -682,7 +685,7 @@ class FormatterDateTest extends TestCase
         }
     }
 
-    public function testIntlTimezoneInputNonDefault()
+    public function testIntlTimezoneInputNonDefault(): void
     {
         $this->testTimezoneInputNonDefault();
     }
@@ -690,7 +693,7 @@ class FormatterDateTest extends TestCase
     /**
      * Test timezones with input date and time in other timezones.
      */
-    public function testTimezoneInputNonDefault()
+    public function testTimezoneInputNonDefault(): void
     {
         $this->formatter->datetimeFormat = 'yyyy-MM-dd HH:mm:ss';
         $this->formatter->dateFormat = 'yyyy-MM-dd';
@@ -733,12 +736,12 @@ class FormatterDateTest extends TestCase
         $this->assertSame('1407674460', $this->formatter->asTimestamp('2014-08-10 12:41:00 UTC'));
     }
 
-    public function testIntlDateOnlyValues()
+    public function testIntlDateOnlyValues(): void
     {
         $this->testDateOnlyValues();
     }
 
-    public function testDateOnlyValues()
+    public function testDateOnlyValues(): void
     {
         date_default_timezone_set('Pacific/Kiritimati');
         // timezones with exactly 24h difference, ensure this test does not fail on a certain time
@@ -765,7 +768,7 @@ class FormatterDateTest extends TestCase
      *
      * @see https://github.com/yiisoft/yii2/issues/13343
      */
-    public function testTimeOnlyValues()
+    public function testTimeOnlyValues(): void
     {
         $this->formatter->defaultTimeZone = 'UTC';
         $this->formatter->timeZone = 'Europe/Zurich'; // UTC+1 (DST UTC+2)
@@ -785,7 +788,7 @@ class FormatterDateTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/15286
      */
-    public function testTimeWithTimezoneInfo()
+    public function testTimeWithTimezoneInfo(): void
     {
         $this->formatter->defaultTimeZone = 'UTC';
         $this->formatter->timeZone = 'Etc/GMT-3';
@@ -799,7 +802,7 @@ class FormatterDateTest extends TestCase
         $this->assertSame('16:22:00', $this->formatter->asTime($time));
     }
 
-    public function testIntlTimeWithTimezoneInfo()
+    public function testIntlTimeWithTimezoneInfo(): void
     {
         $this->testTimeWithTimezoneInfo();
     }
@@ -814,7 +817,7 @@ class FormatterDateTest extends TestCase
      * @dataProvider provideTimezones
      * @param string $dtz
      */
-    public function testIssue6263($dtz)
+    public function testIssue6263($dtz): void
     {
         $this->formatter->defaultTimeZone = $dtz;
 
@@ -829,12 +832,12 @@ class FormatterDateTest extends TestCase
         $this->assertFalse(DateTime::createFromFormat('Y-m-d H:i:s', '2014-05-08'));
     }
 
-    public function testIntlInputFractionSeconds()
+    public function testIntlInputFractionSeconds(): void
     {
         $this->testInputFractionSeconds();
     }
 
-    public function testInputFractionSeconds()
+    public function testInputFractionSeconds(): void
     {
         $this->formatter->defaultTimeZone = 'UTC';
 
@@ -851,12 +854,12 @@ class FormatterDateTest extends TestCase
         $this->assertEquals('2015-04-28 12:06:15+0200', $this->formatter->asDateTime($timeStamp, 'yyyy-MM-dd HH:mm:ssZ'));
     }
 
-    public function testIntlInputUnixTimestamp()
+    public function testIntlInputUnixTimestamp(): void
     {
         $this->testInputUnixTimestamp();
     }
 
-    public function testInputUnixTimestamp()
+    public function testInputUnixTimestamp(): void
     {
         $this->formatter->defaultTimeZone = 'UTC';
         $timeStamp = 1431907200;
diff --git a/tests/framework/i18n/FormatterNumberTest.php b/tests/framework/i18n/FormatterNumberTest.php
index bb96347f46..6aec3faeae 100755
--- a/tests/framework/i18n/FormatterNumberTest.php
+++ b/tests/framework/i18n/FormatterNumberTest.php
@@ -82,14 +82,14 @@ class FormatterNumberTest extends TestCase
      * @dataProvider differentConfigProvider
      * @param array $config
      */
-    public function testIntlAsInteger($config)
+    public function testIntlAsInteger($config): void
     {
         // configure formatter with different configs that should not affect integer format
         Yii::configure($this->formatter, $config);
         $this->testAsInteger();
     }
 
-    public function testAsInteger()
+    public function testAsInteger(): void
     {
         $this->assertSame('123', $this->formatter->asInteger(123));
         $this->assertSame('123', $this->formatter->asInteger(123.00));
@@ -120,10 +120,10 @@ class FormatterNumberTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/16900
      */
-    public function testIntlAsIntegerOptions()
+    public function testIntlAsIntegerOptions(): void
     {
         $this->formatter->numberFormatterTextOptions = [
-            \NumberFormatter::POSITIVE_PREFIX => '+',
+            NumberFormatter::POSITIVE_PREFIX => '+',
         ];
         $this->assertSame('+2', $this->formatter->asInteger(2));
         $this->assertSame('+10', $this->formatter->asInteger(10));
@@ -140,19 +140,19 @@ class FormatterNumberTest extends TestCase
         $this->assertSame('+123,456', $this->formatter->asInteger(123456.789));
     }
 
-    public function testAsIntegerException()
+    public function testAsIntegerException(): void
     {
         $this->expectException('\yii\base\InvalidParamException');
         $this->formatter->asInteger('a');
     }
 
-    public function testAsIntegerException2()
+    public function testAsIntegerException2(): void
     {
         $this->expectException('\yii\base\InvalidParamException');
         $this->formatter->asInteger('-123abc');
     }
 
-    public function testIntlAsDecimal()
+    public function testIntlAsDecimal(): void
     {
         $value = 123.12;
         $this->assertSame('123.12', $this->formatter->asDecimal($value, 2));
@@ -178,7 +178,7 @@ class FormatterNumberTest extends TestCase
         $this->formatter->thousandSeparator = '';
         $this->assertSame('123123,1', $this->formatter->asDecimal($value, 1));
         $this->formatter->thousandSeparator = ' ';
-        $this->assertSame('12 31 23,1', $this->formatter->asDecimal($value, 1, [\NumberFormatter::GROUPING_SIZE => 2]));
+        $this->assertSame('12 31 23,1', $this->formatter->asDecimal($value, 1, [NumberFormatter::GROUPING_SIZE => 2]));
 
         $value = 123123.123;
         $this->formatter->decimalSeparator = ',';
@@ -208,7 +208,7 @@ class FormatterNumberTest extends TestCase
         $this->assertSame('95 836 208 451 783 051,86', $this->formatter->asDecimal('95836208451783051.864'));
     }
 
-    public function testAsDecimal()
+    public function testAsDecimal(): void
     {
         $value = 123.12;
         $this->assertSame('123.12', $this->formatter->asDecimal($value));
@@ -272,12 +272,12 @@ class FormatterNumberTest extends TestCase
         $this->assertSame('95 836 208 451 783 051,86', $this->formatter->asDecimal('95836208451783051.864'));
     }
 
-    public function testIntlAsPercent()
+    public function testIntlAsPercent(): void
     {
         $this->testAsPercent();
     }
 
-    public function testAsPercent()
+    public function testAsPercent(): void
     {
         $this->assertSame('12,300%', $this->formatter->asPercent(123));
         $this->assertSame('12,300%', $this->formatter->asPercent('123'));
@@ -304,7 +304,7 @@ class FormatterNumberTest extends TestCase
         $this->assertSame('9 583 620 845 178 305 186,40%', $this->formatter->asPercent('95836208451783051.864', 2));
     }
 
-    public function testIntlAsCurrency()
+    public function testIntlAsCurrency(): void
     {
         $this->formatter->locale = 'en-US';
         $this->assertSame('$123.00', $this->formatter->asCurrency('123'));
@@ -391,7 +391,7 @@ class FormatterNumberTest extends TestCase
 
         // decimal formatting
         $this->formatter->locale = 'de-DE';
-        $this->assertSame("100\xc2\xa0$", \Yii::$app->formatter->asCurrency(100, 'USD', [
+        $this->assertSame("100\xc2\xa0$", Yii::$app->formatter->asCurrency(100, 'USD', [
             NumberFormatter::MAX_FRACTION_DIGITS => 0,
         ]));
         $this->assertSame("100,00\xc2\xa0$", $this->formatter->asCurrency(100, 'USD', [
@@ -418,7 +418,7 @@ class FormatterNumberTest extends TestCase
         $this->assertIsOneOf($this->formatter->asCurrency('123'), ["123.00\xc2\xa0₽", "123.00\xc2\xa0руб."]);
     }
 
-    public function testAsCurrencyStringFallbackException()
+    public function testAsCurrencyStringFallbackException(): void
     {
         $this->expectException('\yii\base\InvalidConfigException');
         $this->formatter->asCurrency('87654321098765436');
@@ -427,7 +427,7 @@ class FormatterNumberTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/12345
      */
-    public function testIntlCurrencyFraction()
+    public function testIntlCurrencyFraction(): void
     {
         $this->formatter->numberFormatterOptions = [
             NumberFormatter::MIN_FRACTION_DIGITS => 0,
@@ -464,19 +464,19 @@ class FormatterNumberTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/pull/5261
      */
-    public function testIntlIssue5261()
+    public function testIntlIssue5261(): void
     {
         $this->formatter->locale = 'en-US';
         $this->formatter->numberFormatterOptions = [
-            \NumberFormatter::FRACTION_DIGITS => 0,
+            NumberFormatter::FRACTION_DIGITS => 0,
         ];
         $this->formatter->numberFormatterTextOptions = [
-            \NumberFormatter::CURRENCY_CODE => 'EUR',
+            NumberFormatter::CURRENCY_CODE => 'EUR',
         ];
         $this->assertSame('€100', $this->formatter->asCurrency(100, 'EUR'));
     }
 
-    public function testAsCurrency()
+    public function testAsCurrency(): void
     {
         $this->formatter->currencyCode = 'USD';
         $this->assertSame('USD 123.00', $this->formatter->asCurrency('123'));
@@ -514,7 +514,7 @@ class FormatterNumberTest extends TestCase
         $this->assertSame('USD 95 836 208 451 783 051,86', $this->formatter->asCurrency('95836208451783051.864', 'USD'));
     }
 
-    public function testIntlAsScientific()
+    public function testIntlAsScientific(): void
     {
         // see https://github.com/yiisoft/yii2/issues/17708
         $this->markTestSkipped('The test is unreliable since output depends on ICU version');
@@ -533,7 +533,7 @@ class FormatterNumberTest extends TestCase
         $this->assertSame('8.76543210987654E16', $this->formatter->asScientific('87654321098765436'));
     }
 
-    public function testAsScientific()
+    public function testAsScientific(): void
     {
         $this->assertSame('1.23E+2', $this->formatter->asScientific('123', 2));
         $this->assertSame('1.234560E+5', $this->formatter->asScientific('123456'));
@@ -549,14 +549,14 @@ class FormatterNumberTest extends TestCase
         $this->assertSame('8.765432E+16', $this->formatter->asScientific('87654321098765436'));
     }
 
-    public function testAsSpellout()
+    public function testAsSpellout(): void
     {
         $this->expectException('\yii\base\InvalidConfigException');
         $this->expectExceptionMessage('Format as Spellout is only supported when PHP intl extension is installed.');
         $this->formatter->asSpellout(123);
     }
 
-    public function testIntlAsSpellout()
+    public function testIntlAsSpellout(): void
     {
         $this->assertSame('one hundred twenty-three', $this->formatter->asSpellout(123));
 
@@ -567,7 +567,7 @@ class FormatterNumberTest extends TestCase
         $this->assertSame($this->formatter->nullDisplay, $this->formatter->asSpellout(null));
     }
 
-    public function testIntlAsOrdinal()
+    public function testIntlAsOrdinal(): void
     {
         $this->assertSame('0th', $this->formatter->asOrdinal(0));
         $this->assertSame('1st', $this->formatter->asOrdinal(1));
@@ -589,7 +589,7 @@ class FormatterNumberTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/14278
      */
-    public function testIntlAsOrdinalDate()
+    public function testIntlAsOrdinalDate(): void
     {
         $f = $this->formatter;
         $this->assertSame('15th', $f->asOrdinal($f->asDate('2017-05-15', 'php:j')));
@@ -600,11 +600,11 @@ class FormatterNumberTest extends TestCase
         $this->assertSame('1.', $f->asOrdinal($f->asDate('2017-05-01', 'php:j')));
     }
 
-    public function testIntlAsShortSize()
+    public function testIntlAsShortSize(): void
     {
         $this->formatter->numberFormatterOptions = [
-            \NumberFormatter::MIN_FRACTION_DIGITS => 0,
-            \NumberFormatter::MAX_FRACTION_DIGITS => 2,
+            NumberFormatter::MIN_FRACTION_DIGITS => 0,
+            NumberFormatter::MAX_FRACTION_DIGITS => 2,
         ];
 
         // tests for base 1000
@@ -645,7 +645,7 @@ class FormatterNumberTest extends TestCase
         $this->assertSame($this->formatter->nullDisplay, $this->formatter->asShortSize(null));
     }
 
-    public function testAsShortSize()
+    public function testAsShortSize(): void
     {
         // tests for base 1000
         $this->formatter->sizeFormatBase = 1000;
@@ -685,11 +685,11 @@ class FormatterNumberTest extends TestCase
         $this->assertSame($this->formatter->nullDisplay, $this->formatter->asShortSize(null));
     }
 
-    public function testIntlAsSize()
+    public function testIntlAsSize(): void
     {
         $this->formatter->numberFormatterOptions = [
-            \NumberFormatter::MIN_FRACTION_DIGITS => 0,
-            \NumberFormatter::MAX_FRACTION_DIGITS => 2,
+            NumberFormatter::MIN_FRACTION_DIGITS => 0,
+            NumberFormatter::MAX_FRACTION_DIGITS => 2,
         ];
 
         // tests for base 1000
@@ -719,11 +719,11 @@ class FormatterNumberTest extends TestCase
         $this->assertSame($this->formatter->nullDisplay, $this->formatter->asSize(null));
     }
 
-    public function testIntlAsSizeNegative()
+    public function testIntlAsSizeNegative(): void
     {
         $this->formatter->numberFormatterOptions = [
-            \NumberFormatter::MIN_FRACTION_DIGITS => 0,
-            \NumberFormatter::MAX_FRACTION_DIGITS => 2,
+            NumberFormatter::MIN_FRACTION_DIGITS => 0,
+            NumberFormatter::MAX_FRACTION_DIGITS => 2,
         ];
 
         // tests for base 1000
@@ -748,7 +748,7 @@ class FormatterNumberTest extends TestCase
         $this->assertSame('-1,001 kibibytes', $this->formatter->asSize(-1025, 3));
     }
 
-    public function testAsSize()
+    public function testAsSize(): void
     {
         // tests for base 1000
         $this->formatter->sizeFormatBase = 1000;
@@ -778,7 +778,7 @@ class FormatterNumberTest extends TestCase
         $this->assertSame($this->formatter->nullDisplay, $this->formatter->asSize(null));
     }
 
-    public function testAsSizeNegative()
+    public function testAsSizeNegative(): void
     {
         // tests for base 1000
         $this->formatter->sizeFormatBase = 1000;
@@ -803,7 +803,7 @@ class FormatterNumberTest extends TestCase
         $this->assertSame('-1,001 kibibytes', $this->formatter->asSize(-1025, 3));
     }
 
-    public function testIntlAsSizeConfiguration()
+    public function testIntlAsSizeConfiguration(): void
     {
         $this->assertSame('1023 bytes', $this->formatter->asSize(1023));
         $this->assertSame('1023 B', $this->formatter->asShortSize(1023));
@@ -815,7 +815,7 @@ class FormatterNumberTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/4960
      */
-    public function testAsSizeConfiguration()
+    public function testAsSizeConfiguration(): void
     {
         $this->assertSame('1023 bytes', $this->formatter->asSize(1023));
         $this->assertSame('1023 B', $this->formatter->asShortSize(1023));
@@ -863,7 +863,7 @@ class FormatterNumberTest extends TestCase
     /**
      * @dataProvider providerForDirectWrongTypeAttributes
      */
-    public function testIntlAsIntegerDirectWrongTypeAttributes($intOptions, $textOptions, $message)
+    public function testIntlAsIntegerDirectWrongTypeAttributes($intOptions, $textOptions, $message): void
     {
         $this->expectException('yii\base\InvalidArgumentException');
         $this->expectExceptionMessage($message);
@@ -927,7 +927,7 @@ class FormatterNumberTest extends TestCase
     /**
      * @dataProvider providerForConfiguredWrongTypeAttributes
      */
-    public function testIntlAsIntegerConfiguredWrongTypeAttributes($intOptions, $textOptions, $symbols, $message)
+    public function testIntlAsIntegerConfiguredWrongTypeAttributes($intOptions, $textOptions, $symbols, $message): void
     {
         $this->expectException('yii\base\InvalidArgumentException');
         $this->expectExceptionMessage($message);
diff --git a/tests/framework/i18n/FormatterTest.php b/tests/framework/i18n/FormatterTest.php
index 1012d24b94..9621a16581 100644
--- a/tests/framework/i18n/FormatterTest.php
+++ b/tests/framework/i18n/FormatterTest.php
@@ -8,6 +8,11 @@
 
 namespace yiiunit\framework\i18n;
 
+use DateTime;
+use DateTimeZone;
+use NumberFormatter;
+use ResourceBundle;
+use IntlException;
 use yii\i18n\Formatter;
 use yiiunit\TestCase;
 
@@ -46,7 +51,7 @@ class FormatterTest extends TestCase
         IntlTestHelper::resetIntlStatus();
     }
 
-    public function testFormat()
+    public function testFormat(): void
     {
         $value = time();
         $this->assertSame(date('M j, Y', $value), $this->formatter->format($value, 'date'));
@@ -54,7 +59,7 @@ class FormatterTest extends TestCase
         $this->assertSame(date('Y/m/d', $value), $this->formatter->format($value, ['date', 'php:Y/m/d']));
     }
 
-    public function testInvalidFormat()
+    public function testInvalidFormat(): void
     {
         $value = time();
         $this->expectException('\yii\base\InvalidParamException');
@@ -62,7 +67,7 @@ class FormatterTest extends TestCase
         $this->assertSame(date('Y-m-d', $value), $this->formatter->format($value, 'data'));
     }
 
-    public function testInvalidFormatArray()
+    public function testInvalidFormatArray(): void
     {
         $value = time();
         $this->expectException('\yii\base\InvalidParamException');
@@ -70,7 +75,7 @@ class FormatterTest extends TestCase
         $this->assertSame(date('Y-m-d', $value), $this->formatter->format($value, ['data']));
     }
 
-    public function testFormatArrayInvalidStructure()
+    public function testFormatArrayInvalidStructure(): void
     {
         $value = time();
         $this->expectException('\yii\base\InvalidParamException');
@@ -78,7 +83,7 @@ class FormatterTest extends TestCase
         $this->assertSame(date('Y-m-d', $value), $this->formatter->format($value, []));
     }
 
-    public function testClosureFormat()
+    public function testClosureFormat(): void
     {
         $value = time();
         $this->assertSame(date('Y-m-d', $value), $this->formatter->format($value, function ($value) {
@@ -92,7 +97,7 @@ class FormatterTest extends TestCase
         );
     }
 
-    public function testLocale()
+    public function testLocale(): void
     {
         // locale is configured explicitly
         $f = new Formatter(['locale' => 'en-US']);
@@ -103,7 +108,7 @@ class FormatterTest extends TestCase
         $this->assertEquals('ru-RU', $f->locale);
     }
 
-    public function testLanguage()
+    public function testLanguage(): void
     {
         // language is configured explicitly
         $f = new Formatter(['language' => 'en-US']);
@@ -118,7 +123,7 @@ class FormatterTest extends TestCase
         $this->assertEquals('ru-RU', $f->language);
     }
 
-    public function testAsRaw()
+    public function testAsRaw(): void
     {
         $value = '123';
         $this->assertSame($value, $this->formatter->asRaw($value));
@@ -131,7 +136,7 @@ class FormatterTest extends TestCase
         $this->assertSame($this->formatter->nullDisplay, $this->formatter->asRaw(null));
     }
 
-    public function testAsText()
+    public function testAsText(): void
     {
         $value = '123';
         $this->assertSame($value, $this->formatter->asText($value));
@@ -144,7 +149,7 @@ class FormatterTest extends TestCase
         $this->assertSame($this->formatter->nullDisplay, $this->formatter->asText(null));
     }
 
-    public function testAsNtext()
+    public function testAsNtext(): void
     {
         $value = '123';
         $this->assertSame($value, $this->formatter->asNtext($value));
@@ -159,7 +164,7 @@ class FormatterTest extends TestCase
         $this->assertSame($this->formatter->nullDisplay, $this->formatter->asNtext(null));
     }
 
-    public function testAsParagraphs()
+    public function testAsParagraphs(): void
     {
         $value = '123';
         $this->assertSame("<p>$value</p>", $this->formatter->asParagraphs($value));
@@ -190,7 +195,7 @@ class FormatterTest extends TestCase
         $this->assertSame($this->formatter->nullDisplay, $this->formatter->asParagraphs(null));
     }
 
-    public function testAsHtml()
+    public function testAsHtml(): void
     {
         $value = 'no HTML tags';
         $this->assertSame($value, $this->formatter->asHtml($value));
@@ -201,7 +206,7 @@ class FormatterTest extends TestCase
         $this->assertSame('<p>w1 w2</p>', $this->formatter->asHtml('<p>w1 <b>w2</b><br></p>', ['HTML.Allowed' => 'p']));
     }
 
-    public function testAsEmail()
+    public function testAsEmail(): void
     {
         $value = 'test@sample.com';
         $this->assertSame("<a href=\"mailto:$value\">$value</a>", $this->formatter->asEmail($value));
@@ -215,7 +220,7 @@ class FormatterTest extends TestCase
         $this->assertSame($this->formatter->nullDisplay, $this->formatter->asEmail(null));
     }
 
-    public function testAsUrl()
+    public function testAsUrl(): void
     {
         $value = 'http://www.yiiframework.com/';
         $this->assertSame("<a href=\"$value\">$value</a>", $this->formatter->asUrl($value));
@@ -309,7 +314,7 @@ class FormatterTest extends TestCase
         $this->assertSame($this->formatter->nullDisplay, $this->formatter->asUrl(null));
     }
 
-    public function testAsImage()
+    public function testAsImage(): void
     {
         $value = 'http://sample.com/img.jpg';
         $this->assertSame("<img src=\"$value\" alt=\"\">", $this->formatter->asImage($value));
@@ -321,7 +326,7 @@ class FormatterTest extends TestCase
         $this->assertSame($this->formatter->nullDisplay, $this->formatter->asImage(null));
     }
 
-    public function testAsBoolean()
+    public function testAsBoolean(): void
     {
         $this->assertSame('Yes', $this->formatter->asBoolean(true));
         $this->assertSame('No', $this->formatter->asBoolean(false));
@@ -333,7 +338,7 @@ class FormatterTest extends TestCase
         $this->assertSame($this->formatter->nullDisplay, $this->formatter->asBoolean(null));
     }
 
-    public function testAsTimestamp()
+    public function testAsTimestamp(): void
     {
         $this->assertSame('1451606400', $this->formatter->asTimestamp(1451606400));
         $this->assertSame('1451606400', $this->formatter->asTimestamp(1451606400.1234));
@@ -345,10 +350,10 @@ class FormatterTest extends TestCase
 
         $this->assertSame('1451606400', $this->formatter->asTimestamp('2016-01-01 00:00:00'));
 
-        $dateTime = new \DateTime('2016-01-01 00:00:00.000');
+        $dateTime = new DateTime('2016-01-01 00:00:00.000');
         $this->assertSame('1451606400', $this->formatter->asTimestamp($dateTime));
 
-        $dateTime = new \DateTime('2016-01-01 00:00:00.000', new \DateTimeZone('Europe/Berlin'));
+        $dateTime = new DateTime('2016-01-01 00:00:00.000', new DateTimeZone('Europe/Berlin'));
         $this->assertSame('1451602800', $this->formatter->asTimestamp($dateTime));
     }
 
@@ -403,13 +408,13 @@ class FormatterTest extends TestCase
             [
                 'It is possible to change number formatting options',
                 [100, null, [
-                    \NumberFormatter::MIN_FRACTION_DIGITS => 4,
+                    NumberFormatter::MIN_FRACTION_DIGITS => 4,
                 ]], '100.0000 meters', '100.0000 m',
             ],
             [
                 'It is possible to change text options',
                 [-19913.13, null, null, [
-                    \NumberFormatter::NEGATIVE_PREFIX => 'MINUS',
+                    NumberFormatter::NEGATIVE_PREFIX => 'MINUS',
                 ]], 'MINUS19.913 kilometers', 'MINUS19.913 km',
             ],
         ];
@@ -423,7 +428,7 @@ class FormatterTest extends TestCase
      * @param mixed $_shortLength
      * @param mixed $expectedException
      */
-    public function testIntlAsLength($message, $arguments, $expected, $_shortLength, $expectedException = [])
+    public function testIntlAsLength($message, $arguments, $expected, $_shortLength, $expectedException = []): void
     {
         $this->ensureIntlUnitDataIsAvailable();
         if ($expectedException !== []) {
@@ -441,7 +446,7 @@ class FormatterTest extends TestCase
      * @param mixed $expected
      * @param mixed $expectedException
      */
-    public function testIntlAsShortLength($message, $arguments, $_length, $expected, $expectedException = [])
+    public function testIntlAsShortLength($message, $arguments, $_length, $expected, $expectedException = []): void
     {
         $this->ensureIntlUnitDataIsAvailable();
         if ($expectedException !== []) {
@@ -502,13 +507,13 @@ class FormatterTest extends TestCase
             [
                 'It is possible to change number formatting options',
                 [100, null, [
-                    \NumberFormatter::MIN_FRACTION_DIGITS => 4,
+                    NumberFormatter::MIN_FRACTION_DIGITS => 4,
                 ]], '100.0000 kilograms', '100.0000 kg',
             ],
             [
                 'It is possible to change text options',
                 [-19913.13, null, null, [
-                    \NumberFormatter::NEGATIVE_PREFIX => 'MINUS',
+                    NumberFormatter::NEGATIVE_PREFIX => 'MINUS',
                 ]], 'MINUS19.913 tons', 'MINUS19.913 tn',
             ],
         ];
@@ -522,7 +527,7 @@ class FormatterTest extends TestCase
      * @param mixed $_shortWeight
      * @param mixed $expectedException
      */
-    public function testIntlAsWeight($message, $arguments, $expected, $_shortWeight, $expectedException = [])
+    public function testIntlAsWeight($message, $arguments, $expected, $_shortWeight, $expectedException = []): void
     {
         $this->ensureIntlUnitDataIsAvailable();
         if ($expectedException !== []) {
@@ -540,7 +545,7 @@ class FormatterTest extends TestCase
      * @param mixed $expected
      * @param mixed $expectedException
      */
-    public function testIntlAsShortWeight($message, $arguments, $_weight, $expected, $expectedException = [])
+    public function testIntlAsShortWeight($message, $arguments, $_weight, $expected, $expectedException = []): void
     {
         $this->ensureIntlUnitDataIsAvailable();
         if ($expectedException !== []) {
@@ -550,14 +555,14 @@ class FormatterTest extends TestCase
         $this->assertSame($expected, call_user_func_array([$this->formatter, 'asShortWeight'], $arguments), 'Failed asserting that ' . $message);
     }
 
-    public function testAsWeight()
+    public function testAsWeight(): void
     {
         $this->expectException('\yii\base\InvalidConfigException');
         $this->expectExceptionMessage('Format of mass is only supported when PHP intl extension is installed.');
         $this->formatter->asWeight(10);
     }
 
-    public function testAsLength()
+    public function testAsLength(): void
     {
         $this->expectException('\yii\base\InvalidConfigException');
         $this->expectExceptionMessage('Format of length is only supported when PHP intl extension is installed.');
@@ -575,14 +580,14 @@ class FormatterTest extends TestCase
         }
 
         try {
-            $bundle = new \ResourceBundle($this->formatter->locale, 'ICUDATA-unit');
+            $bundle = new ResourceBundle($this->formatter->locale, 'ICUDATA-unit');
             $massUnits = $bundle['units']['mass'];
             $lengthUnits = $bundle['units']['length'];
 
             if ($massUnits === null || $lengthUnits === null) {
                 $skip();
             }
-        } catch (\IntlException $e) {
+        } catch (IntlException $e) {
             $skip();
         }
     }
diff --git a/tests/framework/i18n/GettextMessageSourceTest.php b/tests/framework/i18n/GettextMessageSourceTest.php
index 524338e79b..88aa50bf54 100644
--- a/tests/framework/i18n/GettextMessageSourceTest.php
+++ b/tests/framework/i18n/GettextMessageSourceTest.php
@@ -15,7 +15,7 @@ use yiiunit\TestCase;
  */
 class GettextMessageSourceTest extends TestCase
 {
-    public function testLoadMessages()
+    public function testLoadMessages(): void
     {
         $this->markTestIncomplete();
     }
diff --git a/tests/framework/i18n/GettextMoFileTest.php b/tests/framework/i18n/GettextMoFileTest.php
index adbea31bca..8bfbfd37ac 100644
--- a/tests/framework/i18n/GettextMoFileTest.php
+++ b/tests/framework/i18n/GettextMoFileTest.php
@@ -16,7 +16,7 @@ use yiiunit\TestCase;
  */
 class GettextMoFileTest extends TestCase
 {
-    public function testLoad()
+    public function testLoad(): void
     {
         $moFile = new GettextMoFile();
         $moFilePath = __DIR__ . '/../../data/i18n/test.mo';
@@ -46,7 +46,7 @@ class GettextMoFileTest extends TestCase
         $this->assertTrue(in_array("тест1\\nтест2\n\\\nтест3", $context2));
     }
 
-    public function testSave()
+    public function testSave(): void
     {
         // initial data
         $s = chr(4);
diff --git a/tests/framework/i18n/GettextPoFileTest.php b/tests/framework/i18n/GettextPoFileTest.php
index 11cbebcdbf..e7b913fb62 100644
--- a/tests/framework/i18n/GettextPoFileTest.php
+++ b/tests/framework/i18n/GettextPoFileTest.php
@@ -22,7 +22,7 @@ class GettextPoFileTest extends TestCase
         $this->mockApplication();
     }
 
-    public function testLoad()
+    public function testLoad(): void
     {
         $poFile = new GettextPoFile();
         $poFilePath = __DIR__ . '/../../data/i18n/test.po';
@@ -52,7 +52,7 @@ class GettextPoFileTest extends TestCase
         $this->assertTrue(in_array("тест1\\\nтест2\n\\\\\nтест3", $context2));
     }
 
-    public function testSave()
+    public function testSave(): void
     {
         // initial data
         $s = chr(4);
diff --git a/tests/framework/i18n/I18NTest.php b/tests/framework/i18n/I18NTest.php
index b4f76cdebe..7aea97544b 100644
--- a/tests/framework/i18n/I18NTest.php
+++ b/tests/framework/i18n/I18NTest.php
@@ -50,7 +50,7 @@ class I18NTest extends TestCase
         return PhpMessageSource::className();
     }
 
-    public function testTranslate()
+    public function testTranslate(): void
     {
         $msg = 'The dog runs fast.';
 
@@ -67,7 +67,7 @@ class I18NTest extends TestCase
         $this->assertEquals('Hallo Welt!', $this->i18n->translate('test', 'Hello world!', [], 'de-DE'));
     }
 
-    public function testDefaultSource()
+    public function testDefaultSource(): void
     {
         $i18n = new I18N([
             'translations' => [
@@ -102,7 +102,7 @@ class I18NTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/7964
      */
-    public function testSourceLanguageFallback()
+    public function testSourceLanguageFallback(): void
     {
         $i18n = new I18N([
             'translations' => [
@@ -138,7 +138,7 @@ class I18NTest extends TestCase
         $this->assertEquals($msg, $i18n->translate('test', $msg, [], null));
     }
 
-    public function testTranslateParams()
+    public function testTranslateParams(): void
     {
         $msg = 'His speed is about {n} km/h.';
         $params = ['n' => 42];
@@ -146,7 +146,7 @@ class I18NTest extends TestCase
         $this->assertEquals('Seine Geschwindigkeit beträgt 42 km/h.', $this->i18n->translate('test', $msg, $params, 'de-DE'));
     }
 
-    public function testTranslateParams2()
+    public function testTranslateParams2(): void
     {
         if (!extension_loaded('intl')) {
             $this->markTestSkipped('intl not installed. Skipping.');
@@ -160,7 +160,7 @@ class I18NTest extends TestCase
         $this->assertEquals('Er heißt DA VINCI und ist 42 km/h schnell.', $this->i18n->translate('test', $msg, $params, 'de-DE'));
     }
 
-    public function testSpecialParams()
+    public function testSpecialParams(): void
     {
         $msg = 'His speed is about {0} km/h.';
 
@@ -175,7 +175,7 @@ class I18NTest extends TestCase
      *
      * @see https://github.com/yiisoft/yii2/issues/2209
      */
-    public function testMissingTranslationFormatting()
+    public function testMissingTranslationFormatting(): void
     {
         $this->assertEquals('1 item', $this->i18n->translate('test', '{0, number} {0, plural, one{item} other{items}}', 1, 'hu'));
     }
@@ -183,12 +183,12 @@ class I18NTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/7093
      */
-    public function testRussianPlurals()
+    public function testRussianPlurals(): void
     {
         $this->assertEquals('На диване лежит 6 кошек!', $this->i18n->translate('test', 'There {n, plural, =0{no cats} =1{one cat} other{are # cats}} on lying on the sofa!', ['n' => 6], 'ru'));
     }
 
-    public function testUsingSourceLanguageForMissingTranslation()
+    public function testUsingSourceLanguageForMissingTranslation(): void
     {
         Yii::$app->sourceLanguage = 'ru';
         Yii::$app->language = 'en';
@@ -204,7 +204,7 @@ class I18NTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/2519
      */
-    public function testMissingTranslationEvent()
+    public function testMissingTranslationEvent(): void
     {
         $this->assertEquals('Hallo Welt!', $this->i18n->translate('test', 'Hello world!', [], 'de-DE'));
         $this->assertEquals('Missing translation message.', $this->i18n->translate('test', 'Missing translation message.', [], 'de-DE'));
@@ -242,7 +242,7 @@ class I18NTest extends TestCase
      * @dataProvider sourceLanguageDataProvider
      * @param $sourceLanguage
      */
-    public function testIssue11429($sourceLanguage)
+    public function testIssue11429($sourceLanguage): void
     {
         $this->mockApplication();
         $this->setI18N();
@@ -278,13 +278,13 @@ class I18NTest extends TestCase
      * Formatting a message that contains params but they are not provided.
      * @see https://github.com/yiisoft/yii2/issues/10884
      */
-    public function testFormatMessageWithNoParam()
+    public function testFormatMessageWithNoParam(): void
     {
         $message = 'Incorrect password (length must be from {min, number} to {max, number} symbols).';
         $this->assertEquals($message, $this->i18n->format($message, ['attribute' => 'password'], 'en'));
     }
 
-    public function testFormatMessageWithDottedParameters()
+    public function testFormatMessageWithDottedParameters(): void
     {
         $message = 'date: {dt.test}';
         $this->assertEquals('date: 1510147434', $this->i18n->format($message, ['dt.test' => 1510147434], 'en'));
diff --git a/tests/framework/i18n/IntlTestHelper.php b/tests/framework/i18n/IntlTestHelper.php
index 1d5423a909..e13e3baa16 100644
--- a/tests/framework/i18n/IntlTestHelper.php
+++ b/tests/framework/i18n/IntlTestHelper.php
@@ -21,7 +21,7 @@ namespace yiiunit\framework\i18n {
          * Enable it only for tests prefixed with testIntl.
          * @param Testcase $test
          */
-        public static function setIntlStatus($test)
+        public static function setIntlStatus($test): void
         {
             static::$enableIntl = null;
             if (strncmp($test->getName(false), 'testIntl', 8) === 0) {
@@ -34,7 +34,7 @@ namespace yiiunit\framework\i18n {
             }
         }
 
-        public static function resetIntlStatus()
+        public static function resetIntlStatus(): void
         {
             static::$enableIntl = null;
         }
diff --git a/tests/framework/i18n/LocaleTest.php b/tests/framework/i18n/LocaleTest.php
index a8758db9f5..306d9dc159 100644
--- a/tests/framework/i18n/LocaleTest.php
+++ b/tests/framework/i18n/LocaleTest.php
@@ -38,7 +38,7 @@ class LocaleTest extends TestCase
         $this->locale = null;
     }
 
-    public function testGetCurrencyCode()
+    public function testGetCurrencyCode(): void
     {
         $this->locale->locale = 'de-DE';
         $this->assertSame('€', $this->locale->getCurrencySymbol('EUR'));
diff --git a/tests/framework/i18n/MessageFormatterTest.php b/tests/framework/i18n/MessageFormatterTest.php
index 8b3893b7f5..78358aa707 100644
--- a/tests/framework/i18n/MessageFormatterTest.php
+++ b/tests/framework/i18n/MessageFormatterTest.php
@@ -357,7 +357,7 @@ _MSG_
      * @param bool $skip
      * @param string $skipMessage
      */
-    public function testNamedArguments($pattern, $expected, $args, $skip = false, $skipMessage = '')
+    public function testNamedArguments($pattern, $expected, $args, $skip = false, $skipMessage = ''): void
     {
         if ($skip) {
             $this->markTestSkipped($skipMessage);
@@ -374,7 +374,7 @@ _MSG_
      * @param array $args
      * @param string $locale
      */
-    public function testParseNamedArguments($pattern, $expected, $args, $locale = 'en-US')
+    public function testParseNamedArguments($pattern, $expected, $args, $locale = 'en-US'): void
     {
         if (!extension_loaded('intl')) {
             $this->markTestSkipped('intl not installed. Skipping.');
@@ -385,7 +385,7 @@ _MSG_
         $this->assertEquals($args, $result, $formatter->getErrorMessage() . ' Pattern: ' . $pattern);
     }
 
-    public function testInsufficientArguments()
+    public function testInsufficientArguments(): void
     {
         $expected = '{' . self::SUBJECT . '} is ' . self::N_VALUE;
 
@@ -397,7 +397,7 @@ _MSG_
         $this->assertEquals($expected, $result, $formatter->getErrorMessage());
     }
 
-    public function testNoParams()
+    public function testNoParams(): void
     {
         $pattern = '{' . self::SUBJECT . '} is ' . self::N;
         $formatter = new MessageFormatter();
@@ -405,7 +405,7 @@ _MSG_
         $this->assertEquals($pattern, $result, $formatter->getErrorMessage());
     }
 
-    public function testMalformedFormatter()
+    public function testMalformedFormatter(): void
     {
         $formatter = new MessageFormatter();
         $result = $formatter->format('{word,umber}', ['word' => 'test'], 'en-US'); // typo is intentional, message pattern should be invalid
diff --git a/tests/framework/log/DbTargetTest.php b/tests/framework/log/DbTargetTest.php
index c577e5154d..a740fc66dd 100644
--- a/tests/framework/log/DbTargetTest.php
+++ b/tests/framework/log/DbTargetTest.php
@@ -8,6 +8,11 @@
 
 namespace yiiunit\framework\log;
 
+use yii\console\Application;
+use yii\console\Controller;
+use yii\base\InvalidParamException;
+use yii\db\Exception;
+use yii\base\InvalidConfigException;
 use Yii;
 use yii\db\Connection;
 use yii\db\Query;
@@ -34,7 +39,7 @@ abstract class DbTargetTest extends TestCase
     protected static function runConsoleAction($route, $params = [])
     {
         if (Yii::$app === null) {
-            new \yii\console\Application([
+            new Application([
                 'id' => 'Migrator',
                 'basePath' => '@yiiunit',
                 'controllerMap' => [
@@ -58,7 +63,7 @@ abstract class DbTargetTest extends TestCase
         ob_start();
         $result = Yii::$app->runAction($route, $params);
         echo 'Result is ' . $result;
-        if ($result !== \yii\console\Controller::EXIT_CODE_NORMAL) {
+        if ($result !== Controller::EXIT_CODE_NORMAL) {
             ob_end_flush();
         } else {
             ob_end_clean();
@@ -90,10 +95,10 @@ abstract class DbTargetTest extends TestCase
     }
 
     /**
-     * @throws \yii\base\InvalidParamException
-     * @throws \yii\db\Exception
-     * @throws \yii\base\InvalidConfigException
-     * @return \yii\db\Connection
+     * @throws InvalidParamException
+     * @throws Exception
+     * @throws InvalidConfigException
+     * @return Connection
      */
     public static function getConnection()
     {
@@ -120,7 +125,7 @@ abstract class DbTargetTest extends TestCase
      * Tests that precision isn't lost for log timestamps.
      * @see https://github.com/yiisoft/yii2/issues/7384
      */
-    public function testTimestamp()
+    public function testTimestamp(): void
     {
         $logger = Yii::getLogger();
 
@@ -143,7 +148,7 @@ abstract class DbTargetTest extends TestCase
         static::assertEquals($time, $loggedTime);
     }
 
-    public function testTransactionRollBack()
+    public function testTransactionRollBack(): void
     {
         $db = self::getConnection();
         $logger = Yii::getLogger();
diff --git a/tests/framework/log/DispatcherTest.php b/tests/framework/log/DispatcherTest.php
index dfc46a2ba5..cbd106feb2 100644
--- a/tests/framework/log/DispatcherTest.php
+++ b/tests/framework/log/DispatcherTest.php
@@ -59,7 +59,7 @@ namespace yiiunit\framework\log {
             $this->logger = new Logger();
         }
 
-        public function testConfigureLogger()
+        public function testConfigureLogger(): void
         {
             $dispatcher = new Dispatcher();
             $this->assertSame(Yii::getLogger(), $dispatcher->getLogger());
@@ -92,7 +92,7 @@ namespace yiiunit\framework\log {
         /**
          * @covers \yii\log\Dispatcher::setLogger()
          */
-        public function testSetLogger()
+        public function testSetLogger(): void
         {
             $this->dispatcher->setLogger($this->logger);
             $this->assertSame($this->logger, $this->dispatcher->getLogger());
@@ -112,7 +112,7 @@ namespace yiiunit\framework\log {
         /**
          * @covers \yii\log\Dispatcher::getTraceLevel()
          */
-        public function testGetTraceLevel()
+        public function testGetTraceLevel(): void
         {
             $this->logger->traceLevel = 123;
             $this->dispatcher->setLogger($this->logger);
@@ -122,7 +122,7 @@ namespace yiiunit\framework\log {
         /**
          * @covers \yii\log\Dispatcher::setTraceLevel()
          */
-        public function testSetTraceLevel()
+        public function testSetTraceLevel(): void
         {
             $this->dispatcher->setLogger($this->logger);
             $this->dispatcher->setTraceLevel(123);
@@ -132,7 +132,7 @@ namespace yiiunit\framework\log {
         /**
          * @covers \yii\log\Dispatcher::getFlushInterval()
          */
-        public function testGetFlushInterval()
+        public function testGetFlushInterval(): void
         {
             $this->logger->flushInterval = 99;
             $this->dispatcher->setLogger($this->logger);
@@ -142,7 +142,7 @@ namespace yiiunit\framework\log {
         /**
          * @covers \yii\log\Dispatcher::setFlushInterval()
          */
-        public function testSetFlushInterval()
+        public function testSetFlushInterval(): void
         {
             $this->dispatcher->setLogger($this->logger);
             $this->dispatcher->setFlushInterval(99);
@@ -152,7 +152,7 @@ namespace yiiunit\framework\log {
         /**
          * @covers \yii\log\Dispatcher::dispatch()
          */
-        public function testDispatchWithDisabledTarget()
+        public function testDispatchWithDisabledTarget(): void
         {
             $target = $this->getMockBuilder('yii\\log\\Target')
                 ->setMethods(['collect'])
@@ -168,7 +168,7 @@ namespace yiiunit\framework\log {
         /**
          * @covers \yii\log\Dispatcher::dispatch()
          */
-        public function testDispatchWithSuccessTargetCollect()
+        public function testDispatchWithSuccessTargetCollect(): void
         {
             $target = $this->getMockBuilder('yii\\log\\Target')
                 ->setMethods(['collect'])
@@ -188,7 +188,7 @@ namespace yiiunit\framework\log {
         /**
          * @covers \yii\log\Dispatcher::dispatch()
          */
-        public function testDispatchWithFakeTarget2ThrowExceptionWhenCollect()
+        public function testDispatchWithFakeTarget2ThrowExceptionWhenCollect(): void
         {
             static::$microtimeIsMocked = true;
             $target1 = $this->getMockBuilder('yii\\log\\Target')
@@ -255,7 +255,7 @@ namespace yiiunit\framework\log {
         /**
          * @covers \yii\log\Dispatcher::init()
          */
-        public function testInitWithCreateTargetObject()
+        public function testInitWithCreateTargetObject(): void
         {
             $dispatcher = new Dispatcher(
                 [
@@ -287,7 +287,7 @@ namespace yiiunit\framework\log {
         private $targetThrowFirstCount;
         private $targetThrowSecondOutputs;
 
-        public function testTargetThrow()
+        public function testTargetThrow(): void
         {
             $this->targetThrowFirstCount = 0;
             $this->targetThrowSecondOutputs = [];
diff --git a/tests/framework/log/EmailTargetTest.php b/tests/framework/log/EmailTargetTest.php
index 6d68b2b117..49d81de388 100644
--- a/tests/framework/log/EmailTargetTest.php
+++ b/tests/framework/log/EmailTargetTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\log;
 
+use yii\base\InvalidConfigException;
 use yii\log\EmailTarget;
 use yiiunit\TestCase;
 
@@ -36,7 +37,7 @@ class EmailTargetTest extends TestCase
     /**
      * @covers \yii\log\EmailTarget::init()
      */
-    public function testInitWithOptionTo()
+    public function testInitWithOptionTo(): void
     {
         $target = new EmailTarget(['mailer' => $this->mailer, 'message' => ['to' => 'developer1@example.com']]);
         $this->assertIsObject($target); // should be no exception during `init()`
@@ -45,9 +46,9 @@ class EmailTargetTest extends TestCase
     /**
      * @covers \yii\log\EmailTarget::init()
      */
-    public function testInitWithoutOptionTo()
+    public function testInitWithoutOptionTo(): void
     {
-        $this->expectException(\yii\base\InvalidConfigException::class);
+        $this->expectException(InvalidConfigException::class);
         $this->expectExceptionMessage('The "to" option must be set for EmailTarget::message.');
 
         new EmailTarget(['mailer' => $this->mailer]);
@@ -57,7 +58,7 @@ class EmailTargetTest extends TestCase
      * @covers \yii\log\EmailTarget::export()
      * @covers \yii\log\EmailTarget::composeMessage()
      */
-    public function testExportWithSubject()
+    public function testExportWithSubject(): void
     {
         $message1 = ['A very looooooooooooooooooooooooooooooooooooooooooooooooooooooooooong message 1'];
         $message2 = ['A very looooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong message 2'];
@@ -102,7 +103,7 @@ class EmailTargetTest extends TestCase
      * @covers \yii\log\EmailTarget::export()
      * @covers \yii\log\EmailTarget::composeMessage()
      */
-    public function testExportWithoutSubject()
+    public function testExportWithoutSubject(): void
     {
         $message1 = ['A veeeeery loooooooooooooooooooooooooooooooooooooooooooooooooooooooong message 3'];
         $message2 = ['Message 4'];
@@ -147,7 +148,7 @@ class EmailTargetTest extends TestCase
      *
      * See https://github.com/yiisoft/yii2/issues/14296
      */
-    public function testExportWithSendFailure()
+    public function testExportWithSendFailure(): void
     {
         $message = $this->getMockBuilder('yii\\mail\\BaseMessage')
             ->setMethods(['send'])
diff --git a/tests/framework/log/FileTargetTest.php b/tests/framework/log/FileTargetTest.php
index 13c35d8c01..8e722377dc 100644
--- a/tests/framework/log/FileTargetTest.php
+++ b/tests/framework/log/FileTargetTest.php
@@ -31,7 +31,7 @@ class FileTargetTest extends TestCase
      * Tests that log directory isn't created during init process
      * @see https://github.com/yiisoft/yii2/issues/15662
      */
-    public function testInit()
+    public function testInit(): void
     {
         $logFile = Yii::getAlias('@yiiunit/runtime/log/filetargettest.log');
         FileHelper::removeDirectory(dirname($logFile));
@@ -44,7 +44,7 @@ class FileTargetTest extends TestCase
         );
     }
 
-    public function testRotate()
+    public function testRotate(): void
     {
         $logFile = Yii::getAlias('@yiiunit/runtime/log/filetargettest.log');
         FileHelper::removeDirectory(dirname($logFile));
@@ -113,7 +113,7 @@ class FileTargetTest extends TestCase
         $this->assertFileDoesNotExist($logFile . '.4');
     }
 
-    public function testLogEmptyStrings()
+    public function testLogEmptyStrings(): void
     {
         $logFile = Yii::getAlias('@yiiunit/runtime/log/filetargettest.log');
         $this->clearLogFile($logFile);
@@ -156,7 +156,7 @@ class FileTargetTest extends TestCase
         $this->assertFileDoesNotExist($logFile);
     }
 
-    private function clearLogFile($logFile)
+    private function clearLogFile($logFile): void
     {
         FileHelper::removeDirectory(dirname($logFile));
         mkdir(dirname($logFile), 0777, true);
diff --git a/tests/framework/log/LoggerTest.php b/tests/framework/log/LoggerTest.php
index 5103481124..05c0140d02 100644
--- a/tests/framework/log/LoggerTest.php
+++ b/tests/framework/log/LoggerTest.php
@@ -38,7 +38,7 @@ class LoggerTest extends TestCase
     /**
      * @covers \yii\log\Logger::Log()
      */
-    public function testLog()
+    public function testLog(): void
     {
         $memory = memory_get_usage();
         $this->logger->log('test1', Logger::LEVEL_INFO);
@@ -61,7 +61,7 @@ class LoggerTest extends TestCase
     /**
      * @covers \yii\log\Logger::Log()
      */
-    public function testLogWithTraceLevel()
+    public function testLogWithTraceLevel(): void
     {
         $memory = memory_get_usage();
         $this->logger->traceLevel = 3;
@@ -84,7 +84,7 @@ class LoggerTest extends TestCase
     /**
      * @covers \yii\log\Logger::Log()
      */
-    public function testLogWithFlush()
+    public function testLogWithFlush(): void
     {
         /** @var Logger|\PHPUnit_Framework_MockObject_MockObject $logger */
         $logger = $this->getMockBuilder('yii\log\Logger')
@@ -98,7 +98,7 @@ class LoggerTest extends TestCase
     /**
      * @covers \yii\log\Logger::Flush()
      */
-    public function testFlushWithoutDispatcher()
+    public function testFlushWithoutDispatcher(): void
     {
         $dispatcher = $this->getMockBuilder('\stdClass')->getMock();
         $dispatcher->expects($this->never())->method($this->anything());
@@ -112,7 +112,7 @@ class LoggerTest extends TestCase
     /**
      * @covers \yii\log\Logger::Flush()
      */
-    public function testFlushWithDispatcherAndDefaultParam()
+    public function testFlushWithDispatcherAndDefaultParam(): void
     {
         $message = ['anything'];
         $this->dispatcher->expects($this->once())
@@ -127,7 +127,7 @@ class LoggerTest extends TestCase
     /**
      * @covers \yii\log\Logger::Flush()
      */
-    public function testFlushWithDispatcherAndDefinedParam()
+    public function testFlushWithDispatcherAndDefinedParam(): void
     {
         $message = ['anything'];
         $this->dispatcher->expects($this->once())
@@ -142,7 +142,7 @@ class LoggerTest extends TestCase
     /**
      * @covers \yii\log\Logger::getDbProfiling()
      */
-    public function testGetDbProfiling()
+    public function testGetDbProfiling(): void
     {
         $timings = [
             ['duration' => 5],
@@ -164,7 +164,7 @@ class LoggerTest extends TestCase
     /**
      * @covers \yii\log\Logger::calculateTimings()
      */
-    public function testCalculateTimingsWithEmptyMessages()
+    public function testCalculateTimingsWithEmptyMessages(): void
     {
         $this->assertEmpty($this->logger->calculateTimings([]));
     }
@@ -172,7 +172,7 @@ class LoggerTest extends TestCase
     /**
      * @covers \yii\log\Logger::calculateTimings()
      */
-    public function testCalculateTimingsWithProfileNotBeginOrEnd()
+    public function testCalculateTimingsWithProfileNotBeginOrEnd(): void
     {
         $messages = [
             ['message0', Logger::LEVEL_ERROR, 'category', 'time', 'trace', 1048576],
@@ -190,7 +190,7 @@ class LoggerTest extends TestCase
      *
      * See https://github.com/yiisoft/yii2/issues/14264
      */
-    public function testCalculateTimingsWithProfileBeginEnd()
+    public function testCalculateTimingsWithProfileBeginEnd(): void
     {
         $messages = [
             'anyKey' => ['token', Logger::LEVEL_PROFILE_BEGIN, 'category', 10, 'trace', 1048576],
@@ -236,7 +236,7 @@ class LoggerTest extends TestCase
     /**
      * @covers \yii\log\Logger::calculateTimings()
      */
-    public function testCalculateTimingsWithProfileBeginEndAndNestedLevels()
+    public function testCalculateTimingsWithProfileBeginEndAndNestedLevels(): void
     {
         $messages = [
             ['firstLevel', Logger::LEVEL_PROFILE_BEGIN, 'firstLevelCategory', 10, 'firstTrace', 1048576],
@@ -276,7 +276,7 @@ class LoggerTest extends TestCase
      *
      * @covers \yii\log\Logger::calculateTimings()
      */
-    public function testCalculateTimingsWithProfileBeginEndAndNestedMixedLevels()
+    public function testCalculateTimingsWithProfileBeginEndAndNestedMixedLevels(): void
     {
         $messages = [
             ['firstLevel', Logger::LEVEL_PROFILE_BEGIN, 'firstLevelCategory', 10, 'firstTrace', 1048576],
@@ -314,7 +314,7 @@ class LoggerTest extends TestCase
     /**
      * @covers \yii\log\Logger::getElapsedTime()
      */
-    public function testGetElapsedTime()
+    public function testGetElapsedTime(): void
     {
         $timeBefore = \microtime(true) - YII_BEGIN_TIME;
         usleep(1);
@@ -329,7 +329,7 @@ class LoggerTest extends TestCase
     /**
      * @covers \yii\log\Logger::getLevelName()
      */
-    public function testGetLevelName()
+    public function testGetLevelName(): void
     {
         $this->assertEquals('info', Logger::getLevelName(Logger::LEVEL_INFO));
         $this->assertEquals('error', Logger::getLevelName(Logger::LEVEL_ERROR));
@@ -344,7 +344,7 @@ class LoggerTest extends TestCase
     /**
      * @covers \yii\log\Logger::getProfiling()
      */
-    public function testGetProfilingWithEmptyCategoriesAndExcludeCategories()
+    public function testGetProfilingWithEmptyCategoriesAndExcludeCategories(): void
     {
         $messages = ['anyData'];
         $returnValue = 'return value';
@@ -362,7 +362,7 @@ class LoggerTest extends TestCase
     /**
      * @covers \yii\log\Logger::getProfiling()
      */
-    public function testGetProfilingWithNotEmptyCategoriesAndNotMatched()
+    public function testGetProfilingWithNotEmptyCategoriesAndNotMatched(): void
     {
         $messages = ['anyData'];
         $returnValue = [
@@ -389,7 +389,7 @@ class LoggerTest extends TestCase
     /**
      * @covers \yii\log\Logger::getProfiling()
      */
-    public function testGetProfilingWithNotEmptyCategoriesAndMatched()
+    public function testGetProfilingWithNotEmptyCategoriesAndMatched(): void
     {
         $messages = ['anyData'];
         $matchedByCategoryName = [
@@ -442,7 +442,7 @@ class LoggerTest extends TestCase
     /**
      * @covers \yii\log\Logger::getProfiling()
      */
-    public function testGetProfilingWithNotEmptyCategoriesMatchedAndExcludeCategories()
+    public function testGetProfilingWithNotEmptyCategoriesMatchedAndExcludeCategories(): void
     {
         $messages = ['anyData'];
         $fistCategory = [
@@ -515,7 +515,7 @@ class LoggerTest extends TestCase
     /**
      * @dataProvider providerForNonProfilingMessages
      */
-    public function testGatheringNonProfilingMessages($level)
+    public function testGatheringNonProfilingMessages($level): void
     {
         $logger = new Logger(['flushInterval' => 0]);
         $logger->log('aaa', $level);
@@ -524,7 +524,7 @@ class LoggerTest extends TestCase
         $this->assertCount(2, $logger->messages);
     }
 
-    public function testGatheringProfilingMessages()
+    public function testGatheringProfilingMessages(): void
     {
         $logger = new Logger(['flushInterval' => 0]);
         $logger->log('aaa', Logger::LEVEL_PROFILE_BEGIN);
diff --git a/tests/framework/log/SqliteTargetTest.php b/tests/framework/log/SqliteTargetTest.php
index dce1c15f7e..7df3ca623e 100644
--- a/tests/framework/log/SqliteTargetTest.php
+++ b/tests/framework/log/SqliteTargetTest.php
@@ -17,7 +17,7 @@ class SqliteTargetTest extends DbTargetTest
 {
     protected static $driverName = 'sqlite';
 
-    public function testTransactionRollBack()
+    public function testTransactionRollBack(): void
     {
         if (self::getConnection()->dsn === 'sqlite::memory:') {
             $this->markTestSkipped('It is not possible to test logging during transaction when the DB is in memory');
diff --git a/tests/framework/log/SyslogTargetTest.php b/tests/framework/log/SyslogTargetTest.php
index 4bf0579d49..1d9acaa346 100644
--- a/tests/framework/log/SyslogTargetTest.php
+++ b/tests/framework/log/SyslogTargetTest.php
@@ -61,7 +61,7 @@ namespace yiiunit\framework\log {
         /**
          * @covers \yii\log\SyslogTarget::export()
          */
-        public function testExport()
+        public function testExport(): void
         {
             $identity = 'identity string';
             $options = LOG_ODELAY | LOG_PID;
@@ -149,7 +149,7 @@ namespace yiiunit\framework\log {
          *
          * See https://github.com/yiisoft/yii2/issues/14296
          */
-        public function testFailedExport()
+        public function testFailedExport(): void
         {
             $syslogTarget = $this->getMockBuilder('yii\\log\\SyslogTarget')
                 ->setMethods(['openlog', 'syslog', 'formatMessage', 'closelog'])
@@ -199,7 +199,7 @@ namespace yiiunit\framework\log {
         /**
          * @covers \yii\log\SyslogTarget::formatMessage()
          */
-        public function testFormatMessageWhereTextIsString()
+        public function testFormatMessageWhereTextIsString(): void
         {
             $message = ['text', Logger::LEVEL_INFO, 'category', 'timestamp'];
 
@@ -216,7 +216,7 @@ namespace yiiunit\framework\log {
         /**
          * @covers \yii\log\SyslogTarget::formatMessage()
          */
-        public function testFormatMessageWhereTextIsException()
+        public function testFormatMessageWhereTextIsException(): void
         {
             $exception = new \Exception('exception text');
             $message = [$exception, Logger::LEVEL_INFO, 'category', 'timestamp'];
@@ -234,7 +234,7 @@ namespace yiiunit\framework\log {
         /**
          * @covers \yii\log\SyslogTarget::formatMessage()
          */
-        public function testFormatMessageWhereTextIsNotStringAndNotThrowable()
+        public function testFormatMessageWhereTextIsNotStringAndNotThrowable(): void
         {
             $text = new \stdClass();
             $text->var = 'some text';
diff --git a/tests/framework/log/TargetTest.php b/tests/framework/log/TargetTest.php
index 8e904e0aee..985d440aca 100644
--- a/tests/framework/log/TargetTest.php
+++ b/tests/framework/log/TargetTest.php
@@ -57,7 +57,7 @@ class TargetTest extends TestCase
      * @param array $filter
      * @param array $expected
      */
-    public function testFilter($filter, $expected)
+    public function testFilter($filter, $expected): void
     {
         static::$messages = [];
 
@@ -89,7 +89,7 @@ class TargetTest extends TestCase
         }
     }
 
-    public function testGetContextMessage()
+    public function testGetContextMessage(): void
     {
         $target = new TestTarget([
             'logVars' => [
@@ -147,7 +147,7 @@ class TargetTest extends TestCase
      * @covers \yii\log\Target::setLevels()
      * @covers \yii\log\Target::getLevels()
      */
-    public function testSetupLevelsThroughArray()
+    public function testSetupLevelsThroughArray(): void
     {
         $target = $this->getMockForAbstractClass('yii\\log\\Target');
 
@@ -166,7 +166,7 @@ class TargetTest extends TestCase
      * @covers \yii\log\Target::setLevels()
      * @covers \yii\log\Target::getLevels()
      */
-    public function testSetupLevelsThroughBitmap()
+    public function testSetupLevelsThroughBitmap(): void
     {
         $target = $this->getMockForAbstractClass('yii\\log\\Target');
 
@@ -181,7 +181,7 @@ class TargetTest extends TestCase
         $target->setLevels(128);
     }
 
-    public function testGetEnabled()
+    public function testGetEnabled(): void
     {
         /** @var Target $target */
         $target = $this->getMockForAbstractClass('yii\\log\\Target');
@@ -198,7 +198,7 @@ class TargetTest extends TestCase
         $this->assertTrue($target->enabled);
     }
 
-    public function testFormatMessage()
+    public function testFormatMessage(): void
     {
         /** @var Target $target */
         $target = $this->getMockForAbstractClass('yii\\log\\Target');
@@ -227,7 +227,7 @@ class TargetTest extends TestCase
         $this->assertSame($expectedWithMicro, $formatted);
     }
 
-    public function testCollectMessageStructure()
+    public function testCollectMessageStructure(): void
     {
         $target = new TestTarget(['logVars' => ['_SERVER']]);
         static::$messages = [];
@@ -243,7 +243,7 @@ class TargetTest extends TestCase
         $this->assertCount(6, static::$messages[1]);
     }
 
-    public function testBreakProfilingWithFlushWithProfilingDisabled()
+    public function testBreakProfilingWithFlushWithProfilingDisabled(): void
     {
         $dispatcher = $this->getMockBuilder('yii\log\Dispatcher')
             ->setMethods(['dispatch'])
@@ -265,7 +265,7 @@ class TargetTest extends TestCase
         $logger->log('token.a', Logger::LEVEL_PROFILE_END, 'category');
     }
 
-    public function testNotBreakProfilingWithFlushWithProfilingEnabled()
+    public function testNotBreakProfilingWithFlushWithProfilingEnabled(): void
     {
         $dispatcher = $this->getMockBuilder('yii\log\Dispatcher')
             ->setMethods(['dispatch'])
@@ -300,7 +300,7 @@ class TargetTest extends TestCase
         $logger->log('token.a', Logger::LEVEL_PROFILE_END, 'category');
     }
 
-    public function testFlushingWithProfilingEnabledAndOverflow()
+    public function testFlushingWithProfilingEnabledAndOverflow(): void
     {
         $dispatcher = $this->getMockBuilder('yii\log\Dispatcher')
             ->setMethods(['dispatch'])
@@ -347,7 +347,7 @@ class TargetTest extends TestCase
         $logger->log('token.a', Logger::LEVEL_PROFILE_END, 'category');
     }
 
-    public function testWildcardsInMaskVars()
+    public function testWildcardsInMaskVars(): void
     {
         $keys = [
             'PASSWORD',
@@ -395,7 +395,7 @@ class TestTarget extends Target
      * Exports log [[messages]] to a specific destination.
      * Child classes must implement this method.
      */
-    public function export()
+    public function export(): void
     {
         TargetTest::$messages = array_merge(TargetTest::$messages, $this->messages);
         $this->messages = [];
diff --git a/tests/framework/log/mocks/TargetMock.php b/tests/framework/log/mocks/TargetMock.php
index 86f676ae94..6e49c5b75b 100644
--- a/tests/framework/log/mocks/TargetMock.php
+++ b/tests/framework/log/mocks/TargetMock.php
@@ -15,7 +15,7 @@ class TargetMock extends Target
     {
     }
 
-    public function collect($messages, $final)
+    public function collect($messages, $final): void
     {
         if ($this->collectOverride !== null) {
             call_user_func($this->collectOverride, $messages, $final);
diff --git a/tests/framework/mail/BaseMailerTest.php b/tests/framework/mail/BaseMailerTest.php
index 91f15c836f..ecab9e450e 100644
--- a/tests/framework/mail/BaseMailerTest.php
+++ b/tests/framework/mail/BaseMailerTest.php
@@ -70,7 +70,7 @@ class BaseMailerTest extends TestCase
 
     // Tests :
 
-    public function testSetupView()
+    public function testSetupView(): void
     {
         $mailer = new Mailer();
 
@@ -93,14 +93,14 @@ class BaseMailerTest extends TestCase
     /**
      * @depends testSetupView
      */
-    public function testGetDefaultView()
+    public function testGetDefaultView(): void
     {
         $mailer = new Mailer();
         $view = $mailer->getView();
         $this->assertIsObject($view, 'Unable to get default view!');
     }
 
-    public function testCreateMessage()
+    public function testCreateMessage(): void
     {
         $mailer = new Mailer();
         $message = $mailer->compose();
@@ -111,7 +111,7 @@ class BaseMailerTest extends TestCase
     /**
      * @depends testCreateMessage
      */
-    public function testDefaultMessageConfig()
+    public function testDefaultMessageConfig(): void
     {
         $mailer = new Mailer();
 
@@ -145,7 +145,7 @@ class BaseMailerTest extends TestCase
     /**
      * @depends testGetDefaultView
      */
-    public function testRender()
+    public function testRender(): void
     {
         $mailer = $this->getTestMailComponent();
 
@@ -164,7 +164,7 @@ class BaseMailerTest extends TestCase
     /**
      * @depends testRender
      */
-    public function testRenderLayout()
+    public function testRenderLayout(): void
     {
         $mailer = $this->getTestMailComponent();
 
@@ -188,7 +188,7 @@ class BaseMailerTest extends TestCase
      * @depends testCreateMessage
      * @depends testRender
      */
-    public function testCompose()
+    public function testCompose(): void
     {
         $mailer = $this->getTestMailComponent();
         $mailer->htmlLayout = false;
@@ -258,7 +258,7 @@ TEXT
      * @param string $htmlViewFileContent
      * @param string $expectedTextRendering
      */
-    public function testComposePlainTextFallback($i, $htmlViewFileContent, $expectedTextRendering)
+    public function testComposePlainTextFallback($i, $htmlViewFileContent, $expectedTextRendering): void
     {
         $mailer = $this->getTestMailComponent();
         $mailer->htmlLayout = false;
@@ -275,7 +275,7 @@ TEXT
         $this->assertEqualsWithoutLE($expectedTextRendering, $message->_textBody, 'Unable to render text!');
     }
 
-    public function testUseFileTransport()
+    public function testUseFileTransport(): void
     {
         $mailer = new Mailer();
         $this->assertFalse($mailer->useFileTransport);
@@ -297,7 +297,7 @@ TEXT
         $this->assertStringEqualsFile($file, $message->toString());
     }
 
-    public function testBeforeSendEvent()
+    public function testBeforeSendEvent(): void
     {
         $message = new Message();
 
diff --git a/tests/framework/mail/BaseMessageTest.php b/tests/framework/mail/BaseMessageTest.php
index 39085e0c71..f6e70787a6 100644
--- a/tests/framework/mail/BaseMessageTest.php
+++ b/tests/framework/mail/BaseMessageTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\mail;
 
+use Exception;
 use Yii;
 use yii\mail\BaseMailer;
 use yii\mail\BaseMessage;
@@ -47,7 +48,7 @@ class BaseMessageTest extends TestCase
 
     // Tests :
 
-    public function testSend()
+    public function testSend(): void
     {
         $mailer = $this->getMailer();
         $message = $mailer->compose();
@@ -55,14 +56,14 @@ class BaseMessageTest extends TestCase
         $this->assertEquals($message, $mailer->sentMessages[0], 'Unable to send message!');
     }
 
-    public function testToString()
+    public function testToString(): void
     {
         $mailer = $this->getMailer();
         $message = $mailer->compose();
         $this->assertEquals($message->toString(), '' . $message);
     }
 
-    public function testExceptionToString()
+    public function testExceptionToString(): void
     {
         if (PHP_VERSION_ID < 70400) {
             $this->markTestSkipped('This test is for PHP 7.4+ only');
@@ -70,13 +71,13 @@ class BaseMessageTest extends TestCase
 
         $message = new TestMessageWithException();
 
-        $this->expectException(\Exception::class);
+        $this->expectException(Exception::class);
         $this->expectExceptionMessage('Test exception in toString.');
 
         (string) $message;
     }
 
-    public function testExceptionToStringLegacy()
+    public function testExceptionToStringLegacy(): void
     {
         if (PHP_VERSION_ID >= 70400) {
             $this->markTestSkipped('This test is for PHP < 7.4 only');
@@ -196,12 +197,12 @@ class TestMessage extends BaseMessage
     {
     }
 
-    public function setTextBody($text)
+    public function setTextBody($text): void
     {
         $this->text = $text;
     }
 
-    public function setHtmlBody($html)
+    public function setHtmlBody($html): void
     {
         $this->html = $html;
     }
@@ -232,6 +233,6 @@ class TestMessageWithException extends TestMessage
 {
     public function toString()
     {
-        throw new \Exception('Test exception in toString.');
+        throw new Exception('Test exception in toString.');
     }
 }
diff --git a/tests/framework/models/JsonModel.php b/tests/framework/models/JsonModel.php
index 1319b3897b..1c85db7ac1 100644
--- a/tests/framework/models/JsonModel.php
+++ b/tests/framework/models/JsonModel.php
@@ -8,6 +8,8 @@
 
 namespace yiiunit\framework\models;
 
+use JsonSerializable;
+use ReturnTypeWillChange;
 use yii\base\DynamicModel;
 
 /**
@@ -15,7 +17,7 @@ use yii\base\DynamicModel;
  *
  * {@inheritdoc}
  */
-class JsonModel extends DynamicModel implements \JsonSerializable
+class JsonModel extends DynamicModel implements JsonSerializable
 {
     /**
      * @var array
@@ -25,7 +27,7 @@ class JsonModel extends DynamicModel implements \JsonSerializable
     /**
      * @return array
      */
-    #[\ReturnTypeWillChange]
+    #[ReturnTypeWillChange]
     public function jsonSerialize()
     {
         return $this->data;
@@ -34,7 +36,7 @@ class JsonModel extends DynamicModel implements \JsonSerializable
     /**
      * @inheritdoc
      */
-    public function init()
+    public function init(): void
     {
         $this->defineAttribute('name');
     }
diff --git a/tests/framework/mutex/FileMutexTest.php b/tests/framework/mutex/FileMutexTest.php
index 028f38f5ab..7af8146186 100644
--- a/tests/framework/mutex/FileMutexTest.php
+++ b/tests/framework/mutex/FileMutexTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\mutex;
 
+use Yii;
 use yii\base\InvalidConfigException;
 use yii\mutex\FileMutex;
 use yiiunit\TestCase;
@@ -27,7 +28,7 @@ class FileMutexTest extends TestCase
      */
     protected function createMutex()
     {
-        return \Yii::createObject([
+        return Yii::createObject([
             'class' => FileMutex::className(),
             'mutexPath' => '@yiiunit/runtime/mutex',
         ]);
@@ -39,7 +40,7 @@ class FileMutexTest extends TestCase
      * @param string $mutexName
      * @throws InvalidConfigException
      */
-    public function testDeleteLockFile($mutexName)
+    public function testDeleteLockFile($mutexName): void
     {
         $mutex = $this->createMutex();
         $fileName = $mutex->mutexPath . '/' . md5($mutexName) . '.lock';
diff --git a/tests/framework/mutex/MutexTestTrait.php b/tests/framework/mutex/MutexTestTrait.php
index c12a2b021a..0110115011 100644
--- a/tests/framework/mutex/MutexTestTrait.php
+++ b/tests/framework/mutex/MutexTestTrait.php
@@ -27,7 +27,7 @@ trait MutexTestTrait
      *
      * @param string $mutexName
      */
-    public function testMutexAcquire($mutexName)
+    public function testMutexAcquire($mutexName): void
     {
         $mutex = $this->createMutex();
 
@@ -40,7 +40,7 @@ trait MutexTestTrait
      *
      * @param string $mutexName
      */
-    public function testThatMutexLockIsWorking($mutexName)
+    public function testThatMutexLockIsWorking($mutexName): void
     {
         $mutexOne = $this->createMutex();
         $mutexTwo = $this->createMutex();
@@ -59,7 +59,7 @@ trait MutexTestTrait
      *
      * @param string $mutexName
      */
-    public function testThatMutexLockIsWorkingOnTheSameComponent($mutexName)
+    public function testThatMutexLockIsWorkingOnTheSameComponent($mutexName): void
     {
         $mutex = $this->createMutex();
 
@@ -70,7 +70,7 @@ trait MutexTestTrait
         $this->assertFalse($mutex->release($mutexName));
     }
 
-    public function testTimeout()
+    public function testTimeout(): void
     {
         $mutexName = __FUNCTION__;
         $mutexOne = $this->createMutex();
@@ -90,7 +90,7 @@ trait MutexTestTrait
      *
      * @param string $mutexName
      */
-    public function testMutexIsAcquired($mutexName)
+    public function testMutexIsAcquired($mutexName): void
     {
         $mutexOne = $this->createMutex();
         $mutexTwo = $this->createMutex();
diff --git a/tests/framework/mutex/MysqlMutexTest.php b/tests/framework/mutex/MysqlMutexTest.php
index e3df633ead..8733cb234a 100644
--- a/tests/framework/mutex/MysqlMutexTest.php
+++ b/tests/framework/mutex/MysqlMutexTest.php
@@ -8,6 +8,8 @@
 
 namespace yiiunit\framework\mutex;
 
+use Yii;
+use yii\base\InvalidConfigException;
 use yii\db\Expression;
 use yii\mutex\MysqlMutex;
 use yiiunit\framework\db\DatabaseTestCase;
@@ -28,11 +30,11 @@ class MysqlMutexTest extends DatabaseTestCase
     /**
      * @param array $additionalParams additional params to component create
      * @return MysqlMutex
-     * @throws \yii\base\InvalidConfigException
+     * @throws InvalidConfigException
      */
     protected function createMutex($additionalParams = [])
     {
-        return \Yii::createObject(array_merge([
+        return Yii::createObject(array_merge([
             'class' => MysqlMutex::className(),
             'db' => $this->getConnection(),
         ], $additionalParams));
@@ -43,7 +45,7 @@ class MysqlMutexTest extends DatabaseTestCase
      *
      * @param string $mutexName
      */
-    public function testThatMutexLocksWithKeyPrefixesString($mutexName)
+    public function testThatMutexLocksWithKeyPrefixesString($mutexName): void
     {
         $mutexOne = $this->createMutex(['keyPrefix' => 'a']);
         $mutexTwo = $this->createMutex(['keyPrefix' => 'b']);
@@ -59,7 +61,7 @@ class MysqlMutexTest extends DatabaseTestCase
      *
      * @param string $mutexName
      */
-    public function testThatMutexLocksWithKeyPrefixesLongString($mutexName)
+    public function testThatMutexLocksWithKeyPrefixesLongString($mutexName): void
     {
         $mutexOne = $this->createMutex(['keyPrefix' => str_repeat('a', 40)]);
         $mutexTwo = $this->createMutex(['keyPrefix' => str_repeat('b', 40)]);
@@ -75,7 +77,7 @@ class MysqlMutexTest extends DatabaseTestCase
      *
      * @param string $mutexName
      */
-    public function testThatMutexLocksWithKeyPrefixesExpression($mutexName)
+    public function testThatMutexLocksWithKeyPrefixesExpression($mutexName): void
     {
         $mutexOne = $this->createMutex(['keyPrefix' => new Expression('1+1')]);
         $mutexTwo = $this->createMutex(['keyPrefix' => new Expression('1+2')]);
@@ -91,7 +93,7 @@ class MysqlMutexTest extends DatabaseTestCase
      *
      * @param string $mutexName
      */
-    public function testThatMutexLocksWithKeyPrefixesExpressionCalculatedValue($mutexName)
+    public function testThatMutexLocksWithKeyPrefixesExpressionCalculatedValue($mutexName): void
     {
         $mutexOne = $this->createMutex(['keyPrefix' => new Expression('1+1')]);
         $mutexTwo = $this->createMutex(['keyPrefix' => new Expression('1*2')]);
@@ -101,7 +103,7 @@ class MysqlMutexTest extends DatabaseTestCase
         $this->assertTrue($mutexOne->release($mutexName));
     }
 
-    public function testCreateMutex()
+    public function testCreateMutex(): void
     {
         $mutex = $this->createMutex(['keyPrefix' => new Expression('1+1')]);
         $this->assertInstanceOf(MysqlMutex::classname(), $mutex);
diff --git a/tests/framework/mutex/PgsqlMutexTest.php b/tests/framework/mutex/PgsqlMutexTest.php
index 5df78b6b1d..73f155cde1 100644
--- a/tests/framework/mutex/PgsqlMutexTest.php
+++ b/tests/framework/mutex/PgsqlMutexTest.php
@@ -8,6 +8,8 @@
 
 namespace yiiunit\framework\mutex;
 
+use Yii;
+use yii\base\InvalidConfigException;
 use yii\mutex\PgsqlMutex;
 use yiiunit\framework\db\DatabaseTestCase;
 
@@ -26,11 +28,11 @@ class PgsqlMutexTest extends DatabaseTestCase
 
     /**
      * @return PgsqlMutex
-     * @throws \yii\base\InvalidConfigException
+     * @throws InvalidConfigException
      */
     protected function createMutex()
     {
-        return \Yii::createObject([
+        return Yii::createObject([
             'class' => PgsqlMutex::className(),
             'db' => $this->getConnection(),
         ]);
diff --git a/tests/framework/mutex/RetryAcquireTraitTest.php b/tests/framework/mutex/RetryAcquireTraitTest.php
index dbf4486daa..26ec61a3d5 100644
--- a/tests/framework/mutex/RetryAcquireTraitTest.php
+++ b/tests/framework/mutex/RetryAcquireTraitTest.php
@@ -25,7 +25,7 @@ class RetryAcquireTraitTest extends TestCase
     /**
      * @throws InvalidConfigException
      */
-    public function testRetryAcquire()
+    public function testRetryAcquire(): void
     {
         $mutexName = __FUNCTION__;
         $mutexOne = $this->createMutex();
diff --git a/tests/framework/rbac/DbManagerTestCase.php b/tests/framework/rbac/DbManagerTestCase.php
index 8a7ee670c0..55a509f86a 100644
--- a/tests/framework/rbac/DbManagerTestCase.php
+++ b/tests/framework/rbac/DbManagerTestCase.php
@@ -8,6 +8,10 @@
 
 namespace yiiunit\framework\rbac;
 
+use yii\base\InvalidParamException;
+use yii\db\Exception;
+use yii\base\InvalidConfigException;
+use yii\rbac\ManagerInterface;
 use Yii;
 use yii\caching\ArrayCache;
 use yii\console\Application;
@@ -37,7 +41,7 @@ abstract class DbManagerTestCase extends ManagerTestCase
      */
     protected $db;
 
-    public function testGetAssignmentsByRole()
+    public function testGetAssignmentsByRole(): void
     {
         $this->prepareData();
         $reader = $this->auth->getRole('reader');
@@ -122,10 +126,10 @@ abstract class DbManagerTestCase extends ManagerTestCase
     }
 
     /**
-     * @throws \yii\base\InvalidParamException
-     * @throws \yii\db\Exception
-     * @throws \yii\base\InvalidConfigException
-     * @return \yii\db\Connection
+     * @throws InvalidParamException
+     * @throws Exception
+     * @throws InvalidConfigException
+     * @return Connection
      */
     public function getConnection()
     {
@@ -155,14 +159,14 @@ abstract class DbManagerTestCase extends ManagerTestCase
     }
 
     /**
-     * @return \yii\rbac\ManagerInterface
+     * @return ManagerInterface
      */
     protected function createManager()
     {
         return new DbManager(['db' => $this->getConnection(), 'defaultRoles' => ['myDefaultRole']]);
     }
 
-    private function prepareRoles($userId)
+    private function prepareRoles($userId): void
     {
         $this->auth->removeAll();
 
@@ -194,7 +198,7 @@ abstract class DbManagerTestCase extends ManagerTestCase
      * @param mixed $searchUserId
      * @param mixed $isValid
      */
-    public function testGetPermissionsByUserWithEmptyValue($userId, $searchUserId, $isValid)
+    public function testGetPermissionsByUserWithEmptyValue($userId, $searchUserId, $isValid): void
     {
         $this->prepareRoles($userId);
 
@@ -214,7 +218,7 @@ abstract class DbManagerTestCase extends ManagerTestCase
      * @param mixed $searchUserId
      * @param mixed $isValid
      */
-    public function testGetRolesByUserWithEmptyValue($userId, $searchUserId, $isValid)
+    public function testGetRolesByUserWithEmptyValue($userId, $searchUserId, $isValid): void
     {
         $this->prepareRoles($userId);
 
@@ -228,7 +232,7 @@ abstract class DbManagerTestCase extends ManagerTestCase
         }
     }
 
-    public function testGetCachedRolesByUserId()
+    public function testGetCachedRolesByUserId(): void
     {
         $this->auth->removeAll();
         $this->auth->cache = new ArrayCache();
@@ -266,7 +270,7 @@ abstract class DbManagerTestCase extends ManagerTestCase
      * @param mixed $searchUserId
      * @param mixed $isValid
      */
-    public function testGetAssignmentWithEmptyValue($userId, $searchUserId, $isValid)
+    public function testGetAssignmentWithEmptyValue($userId, $searchUserId, $isValid): void
     {
         $this->prepareRoles($userId);
 
@@ -286,7 +290,7 @@ abstract class DbManagerTestCase extends ManagerTestCase
      * @param mixed $searchUserId
      * @param mixed $isValid
      */
-    public function testGetAssignmentsWithEmptyValue($userId, $searchUserId, $isValid)
+    public function testGetAssignmentsWithEmptyValue($userId, $searchUserId, $isValid): void
     {
         $this->prepareRoles($userId);
 
@@ -307,7 +311,7 @@ abstract class DbManagerTestCase extends ManagerTestCase
      * @param mixed $searchUserId
      * @param mixed $isValid
      */
-    public function testRevokeWithEmptyValue($userId, $searchUserId, $isValid)
+    public function testRevokeWithEmptyValue($userId, $searchUserId, $isValid): void
     {
         $this->prepareRoles($userId);
         $role = $this->auth->getRole('Author');
@@ -327,7 +331,7 @@ abstract class DbManagerTestCase extends ManagerTestCase
      * @param mixed $searchUserId
      * @param mixed $isValid
      */
-    public function testRevokeAllWithEmptyValue($userId, $searchUserId, $isValid)
+    public function testRevokeAllWithEmptyValue($userId, $searchUserId, $isValid): void
     {
         $this->prepareRoles($userId);
 
@@ -343,7 +347,7 @@ abstract class DbManagerTestCase extends ManagerTestCase
     /**
      * Ensure assignments are read from DB only once on subsequent tests.
      */
-    public function testCheckAccessCache()
+    public function testCheckAccessCache(): void
     {
         $this->mockApplication();
         $this->prepareData();
@@ -402,7 +406,7 @@ abstract class DbManagerTestCase extends ManagerTestCase
         $this->assertSingleQueryToAssignmentsTable($logTarget);
     }
 
-    private function assertSingleQueryToAssignmentsTable($logTarget)
+    private function assertSingleQueryToAssignmentsTable($logTarget): void
     {
         $messages = array_filter($logTarget->messages, function ($message) {
             return strpos($message[0], 'auth_assignment') !== false;
diff --git a/tests/framework/rbac/ExposedPhpManager.php b/tests/framework/rbac/ExposedPhpManager.php
index a07cbc00be..685b3e93da 100644
--- a/tests/framework/rbac/ExposedPhpManager.php
+++ b/tests/framework/rbac/ExposedPhpManager.php
@@ -8,6 +8,9 @@
 
 namespace yiiunit\framework\rbac;
 
+use yii\rbac\Item;
+use yii\rbac\Assignment;
+use yii\rbac\Rule;
 use yii\rbac\PhpManager;
 
 /**
@@ -16,7 +19,7 @@ use yii\rbac\PhpManager;
 class ExposedPhpManager extends PhpManager
 {
     /**
-     * @var \yii\rbac\Item[]
+     * @var Item[]
      */
     public $items = []; // itemName => item
     /**
@@ -24,20 +27,20 @@ class ExposedPhpManager extends PhpManager
      */
     public $children = []; // itemName, childName => child
     /**
-     * @var \yii\rbac\Assignment[]
+     * @var Assignment[]
      */
     public $assignments = []; // userId, itemName => assignment
     /**
-     * @var \yii\rbac\Rule[]
+     * @var Rule[]
      */
     public $rules = []; // ruleName => rule
 
-    public function load()
+    public function load(): void
     {
         parent::load();
     }
 
-    public function save()
+    public function save(): void
     {
         parent::save();
     }
diff --git a/tests/framework/rbac/ManagerTestCase.php b/tests/framework/rbac/ManagerTestCase.php
index 070d23e64c..81a4462711 100644
--- a/tests/framework/rbac/ManagerTestCase.php
+++ b/tests/framework/rbac/ManagerTestCase.php
@@ -8,6 +8,9 @@
 
 namespace yiiunit\framework\rbac;
 
+use Yii;
+use InvalidArgumentException;
+use yii\rbac\ManagerInterface;
 use yii\rbac\BaseManager;
 use yii\rbac\Item;
 use yii\rbac\Permission;
@@ -20,16 +23,16 @@ use yiiunit\TestCase;
 abstract class ManagerTestCase extends TestCase
 {
     /**
-     * @var \yii\rbac\ManagerInterface|BaseManager
+     * @var ManagerInterface|BaseManager
      */
     protected $auth;
 
     /**
-     * @return \yii\rbac\ManagerInterface
+     * @return ManagerInterface
      */
     abstract protected function createManager();
 
-    public function testCreateRole()
+    public function testCreateRole(): void
     {
         $role = $this->auth->createRole('admin');
         $this->assertInstanceOf(Role::className(), $role);
@@ -37,7 +40,7 @@ abstract class ManagerTestCase extends TestCase
         $this->assertEquals('admin', $role->name);
     }
 
-    public function testCreatePermission()
+    public function testCreatePermission(): void
     {
         $permission = $this->auth->createPermission('edit post');
         $this->assertInstanceOf(Permission::className(), $permission);
@@ -45,7 +48,7 @@ abstract class ManagerTestCase extends TestCase
         $this->assertEquals('edit post', $permission->name);
     }
 
-    public function testAdd()
+    public function testAdd(): void
     {
         $role = $this->auth->createRole('admin');
         $role->description = 'administrator';
@@ -61,7 +64,7 @@ abstract class ManagerTestCase extends TestCase
         // todo: check duplication of name
     }
 
-    public function testGetChildren()
+    public function testGetChildren(): void
     {
         $user = $this->auth->createRole('user');
         $this->auth->add($user);
@@ -73,7 +76,7 @@ abstract class ManagerTestCase extends TestCase
         $this->assertCount(1, $this->auth->getChildren($user->name));
     }
 
-    public function testGetRule()
+    public function testGetRule(): void
     {
         $this->prepareData();
 
@@ -85,7 +88,7 @@ abstract class ManagerTestCase extends TestCase
         $this->assertNull($rule);
     }
 
-    public function testAddRule()
+    public function testAddRule(): void
     {
         $this->prepareData();
 
@@ -98,7 +101,7 @@ abstract class ManagerTestCase extends TestCase
         $this->assertTrue($rule->reallyReally);
     }
 
-    public function testUpdateRule()
+    public function testUpdateRule(): void
     {
         $this->prepareData();
 
@@ -131,7 +134,7 @@ abstract class ManagerTestCase extends TestCase
         $this->assertEquals('new createPost', $item->name);
     }
 
-    public function testGetRules()
+    public function testGetRules(): void
     {
         $this->prepareData();
 
@@ -149,7 +152,7 @@ abstract class ManagerTestCase extends TestCase
         $this->assertContains('isAuthor', $ruleNames);
     }
 
-    public function testRemoveRule()
+    public function testRemoveRule(): void
     {
         $this->prepareData();
 
@@ -163,7 +166,7 @@ abstract class ManagerTestCase extends TestCase
         $this->assertNull($item);
     }
 
-    public function testCheckAccess()
+    public function testCheckAccess(): void
     {
         $this->prepareData();
 
@@ -268,7 +271,7 @@ abstract class ManagerTestCase extends TestCase
         $this->auth->assign($admin, 'admin C');
     }
 
-    public function testGetPermissionsByRole()
+    public function testGetPermissionsByRole(): void
     {
         $this->prepareData();
         $permissions = $this->auth->getPermissionsByRole('admin');
@@ -279,7 +282,7 @@ abstract class ManagerTestCase extends TestCase
         }
     }
 
-    public function testGetPermissionsByUser()
+    public function testGetPermissionsByUser(): void
     {
         $this->prepareData();
         $permissions = $this->auth->getPermissionsByUser('author B');
@@ -290,7 +293,7 @@ abstract class ManagerTestCase extends TestCase
         }
     }
 
-    public function testGetRole()
+    public function testGetRole(): void
     {
         $this->prepareData();
         $author = $this->auth->getRole('author');
@@ -299,7 +302,7 @@ abstract class ManagerTestCase extends TestCase
         $this->assertEquals('authorData', $author->data);
     }
 
-    public function testGetPermission()
+    public function testGetPermission(): void
     {
         $this->prepareData();
         $createPost = $this->auth->getPermission('createPost');
@@ -308,7 +311,7 @@ abstract class ManagerTestCase extends TestCase
         $this->assertEquals('createPostData', $createPost->data);
     }
 
-    public function testGetRolesByUser()
+    public function testGetRolesByUser(): void
     {
         $this->prepareData();
         $reader = $this->auth->getRole('reader');
@@ -330,7 +333,7 @@ abstract class ManagerTestCase extends TestCase
         $this->assertContains('myDefaultRole', array_keys($roles));
     }
 
-    public function testGetChildRoles()
+    public function testGetChildRoles(): void
     {
         $this->prepareData();
 
@@ -356,7 +359,7 @@ abstract class ManagerTestCase extends TestCase
         $this->assertArrayHasKey('reader', $roles);
     }
 
-    public function testAssignMultipleRoles()
+    public function testAssignMultipleRoles(): void
     {
         $this->prepareData();
 
@@ -385,7 +388,7 @@ abstract class ManagerTestCase extends TestCase
         );
     }
 
-    public function testAssignmentsToIntegerId()
+    public function testAssignmentsToIntegerId(): void
     {
         $this->prepareData();
 
@@ -402,7 +405,7 @@ abstract class ManagerTestCase extends TestCase
         $this->assertCount(2, $this->auth->getAssignments(1337));
     }
 
-    public function testGetAssignmentsByRole()
+    public function testGetAssignmentsByRole(): void
     {
         $this->prepareData();
         $reader = $this->auth->getRole('reader');
@@ -416,7 +419,7 @@ abstract class ManagerTestCase extends TestCase
         $this->assertEquals(['admin C'], $this->auth->getUserIdsByRole('admin'));
     }
 
-    public function testCanAddChild()
+    public function testCanAddChild(): void
     {
         $this->prepareData();
 
@@ -427,7 +430,7 @@ abstract class ManagerTestCase extends TestCase
         $this->assertFalse($this->auth->canAddChild($reader, $author));
     }
 
-    public function testRemoveAllRules()
+    public function testRemoveAllRules(): void
     {
         $this->prepareData();
 
@@ -439,7 +442,7 @@ abstract class ManagerTestCase extends TestCase
         $this->assertNotEmpty($this->auth->getPermissions());
     }
 
-    public function testRemoveAllRoles()
+    public function testRemoveAllRoles(): void
     {
         $this->prepareData();
 
@@ -451,7 +454,7 @@ abstract class ManagerTestCase extends TestCase
         $this->assertNotEmpty($this->auth->getPermissions());
     }
 
-    public function testRemoveAllPermissions()
+    public function testRemoveAllPermissions(): void
     {
         $this->prepareData();
 
@@ -475,7 +478,7 @@ abstract class ManagerTestCase extends TestCase
      * @dataProvider RBACItemsProvider
      * @param mixed $RBACItemType
      */
-    public function testAssignRule($RBACItemType)
+    public function testAssignRule($RBACItemType): void
     {
         $auth = $this->auth;
         $userId = 3;
@@ -507,9 +510,9 @@ abstract class ManagerTestCase extends TestCase
         $this->assertFalse($auth->checkAccess($userId, 'Reader', ['action' => 'write']));
 
         // using DI
-        \Yii::$container->set('write_rule', ['class' => 'yiiunit\framework\rbac\ActionRule', 'action' => 'write']);
-        \Yii::$container->set('delete_rule', ['class' => 'yiiunit\framework\rbac\ActionRule', 'action' => 'delete']);
-        \Yii::$container->set('all_rule', ['class' => 'yiiunit\framework\rbac\ActionRule', 'action' => 'all']);
+        Yii::$container->set('write_rule', ['class' => 'yiiunit\framework\rbac\ActionRule', 'action' => 'write']);
+        Yii::$container->set('delete_rule', ['class' => 'yiiunit\framework\rbac\ActionRule', 'action' => 'delete']);
+        Yii::$container->set('all_rule', ['class' => 'yiiunit\framework\rbac\ActionRule', 'action' => 'all']);
 
         $item = $this->createRBACItem($RBACItemType, 'Writer');
         $item->ruleName = 'write_rule';
@@ -543,7 +546,7 @@ abstract class ManagerTestCase extends TestCase
      * @dataProvider RBACItemsProvider
      * @param mixed $RBACItemType
      */
-    public function testRevokeRule($RBACItemType)
+    public function testRevokeRule($RBACItemType): void
     {
         $userId = 3;
         $auth = $this->auth;
@@ -584,7 +587,7 @@ abstract class ManagerTestCase extends TestCase
             return $this->auth->createPermission($name);
         }
 
-        throw new \InvalidArgumentException();
+        throw new InvalidArgumentException();
     }
 
     /**
@@ -602,14 +605,14 @@ abstract class ManagerTestCase extends TestCase
             return $this->auth->getPermission($name);
         }
 
-        throw new \InvalidArgumentException();
+        throw new InvalidArgumentException();
     }
 
     /**
      * @see https://github.com/yiisoft/yii2/issues/10176
      * @see https://github.com/yiisoft/yii2/issues/12681
      */
-    public function testRuleWithPrivateFields()
+    public function testRuleWithPrivateFields(): void
     {
         $auth = $this->auth;
 
@@ -623,7 +626,7 @@ abstract class ManagerTestCase extends TestCase
         $this->assertInstanceOf(ActionRule::className(), $rule);
     }
 
-    public function testDefaultRolesWithClosureReturningNonArrayValue()
+    public function testDefaultRolesWithClosureReturningNonArrayValue(): void
     {
         $this->expectException('yii\base\InvalidValueException');
         $this->expectExceptionMessage('Default roles closure must return an array');
@@ -632,7 +635,7 @@ abstract class ManagerTestCase extends TestCase
         };
     }
 
-    public function testDefaultRolesWithNonArrayValue()
+    public function testDefaultRolesWithNonArrayValue(): void
     {
         $this->expectException('yii\base\InvalidArgumentException');
         $this->expectExceptionMessage('Default roles must be either an array or a callable');
diff --git a/tests/framework/rbac/MySQLManagerCacheTest.php b/tests/framework/rbac/MySQLManagerCacheTest.php
index 4ae2819b72..5832a09dc4 100644
--- a/tests/framework/rbac/MySQLManagerCacheTest.php
+++ b/tests/framework/rbac/MySQLManagerCacheTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\rbac;
 
+use yii\rbac\ManagerInterface;
 use yii\caching\FileCache;
 use yii\rbac\DbManager;
 
@@ -20,7 +21,7 @@ use yii\rbac\DbManager;
 class MySQLManagerCacheTest extends MySQLManagerTest
 {
     /**
-     * @return \yii\rbac\ManagerInterface
+     * @return ManagerInterface
      */
     protected function createManager()
     {
diff --git a/tests/framework/rbac/PgSQLManagerCacheTest.php b/tests/framework/rbac/PgSQLManagerCacheTest.php
index 3c5dce8f52..b22baff70d 100644
--- a/tests/framework/rbac/PgSQLManagerCacheTest.php
+++ b/tests/framework/rbac/PgSQLManagerCacheTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\rbac;
 
+use yii\rbac\ManagerInterface;
 use yii\caching\FileCache;
 use yii\rbac\DbManager;
 
@@ -22,7 +23,7 @@ class PgSQLManagerCacheTest extends DbManagerTestCase
     protected static $driverName = 'pgsql';
 
     /**
-     * @return \yii\rbac\ManagerInterface
+     * @return ManagerInterface
      */
     protected function createManager()
     {
diff --git a/tests/framework/rbac/PhpManagerTest.php b/tests/framework/rbac/PhpManagerTest.php
index 493d5dcb80..99274307ea 100644
--- a/tests/framework/rbac/PhpManagerTest.php
+++ b/tests/framework/rbac/PhpManagerTest.php
@@ -98,7 +98,7 @@ class PhpManagerTest extends ManagerTestCase
         parent::tearDown();
     }
 
-    public function testSaveLoad()
+    public function testSaveLoad(): void
     {
         static::$time = static::$filemtime = \time();
 
@@ -118,7 +118,7 @@ class PhpManagerTest extends ManagerTestCase
         $this->assertEquals($rules, $this->auth->rules);
     }
 
-    public function testUpdateItemName()
+    public function testUpdateItemName(): void
     {
         $this->prepareData();
 
@@ -128,7 +128,7 @@ class PhpManagerTest extends ManagerTestCase
         $this->assertTrue($this->auth->update($name, $permission), 'You should be able to update name.');
     }
 
-    public function testUpdateDescription()
+    public function testUpdateDescription(): void
     {
         $this->prepareData();
         $name = 'readPost';
@@ -137,7 +137,7 @@ class PhpManagerTest extends ManagerTestCase
         $this->assertTrue($this->auth->update($name, $permission), 'You should be able to save w/o changing name.');
     }
 
-    public function testOverwriteName()
+    public function testOverwriteName(): void
     {
         $this->prepareData();
 
@@ -150,7 +150,7 @@ class PhpManagerTest extends ManagerTestCase
         $this->auth->update($name, $permission);
     }
 
-    public function testSaveAssignments()
+    public function testSaveAssignments(): void
     {
         $this->auth->removeAll();
         $role = $this->auth->createRole('Admin');
diff --git a/tests/framework/requirements/YiiRequirementCheckerTest.php b/tests/framework/requirements/YiiRequirementCheckerTest.php
index 93be8d23ad..c611a01863 100644
--- a/tests/framework/requirements/YiiRequirementCheckerTest.php
+++ b/tests/framework/requirements/YiiRequirementCheckerTest.php
@@ -17,7 +17,7 @@ use yiiunit\TestCase;
  */
 class YiiRequirementCheckerTest extends TestCase
 {
-    public function testCheck()
+    public function testCheck(): void
     {
         $requirementsChecker = new YiiRequirementChecker();
 
@@ -67,7 +67,7 @@ class YiiRequirementCheckerTest extends TestCase
     /**
      * @depends testCheck
      */
-    public function testCheckEval()
+    public function testCheckEval(): void
     {
         $requirementsChecker = new YiiRequirementChecker();
 
@@ -101,7 +101,7 @@ class YiiRequirementCheckerTest extends TestCase
     /**
      * @depends testCheck
      */
-    public function testCheckChained()
+    public function testCheckChained(): void
     {
         $requirementsChecker = new YiiRequirementChecker();
 
@@ -133,7 +133,7 @@ class YiiRequirementCheckerTest extends TestCase
         }
     }
 
-    public function testCheckPhpExtensionVersion()
+    public function testCheckPhpExtensionVersion(): void
     {
         if (defined('HHVM_VERSION')) {
             $this->markTestSkipped('Can not test this on HHVM.');
@@ -168,7 +168,7 @@ class YiiRequirementCheckerTest extends TestCase
      * @param string  $verboseValue     verbose value.
      * @param int $expectedByteSize expected byte size.
      */
-    public function testGetByteSize($verboseValue, $expectedByteSize)
+    public function testGetByteSize($verboseValue, $expectedByteSize): void
     {
         $requirementsChecker = new YiiRequirementChecker();
 
@@ -199,7 +199,7 @@ class YiiRequirementCheckerTest extends TestCase
      * @param string  $compare                  comparison.
      * @param bool $expectedComparisonResult expected comparison result.
      */
-    public function testCompareByteSize($a, $b, $compare, $expectedComparisonResult)
+    public function testCompareByteSize($a, $b, $compare, $expectedComparisonResult): void
     {
         $requirementsChecker = new YiiRequirementChecker();
         $this->assertEquals($expectedComparisonResult, $requirementsChecker->compareByteSize($a, $b, $compare), "Wrong compare '{$a}{$compare}{$b}'");
diff --git a/tests/framework/rest/IndexActionTest.php b/tests/framework/rest/IndexActionTest.php
index 84fb987ead..efa3a17c7e 100644
--- a/tests/framework/rest/IndexActionTest.php
+++ b/tests/framework/rest/IndexActionTest.php
@@ -39,7 +39,7 @@ class IndexActionTest extends TestCase
         Yii::$app->getDb()->createCommand()->createTable(IndexActionModel::tableName(), $columns)->execute();
     }
 
-    public function testPrepareSearchQueryAttribute()
+    public function testPrepareSearchQueryAttribute(): void
     {
         $sql = '';
         Yii::$app->controller = new RestController(
@@ -83,7 +83,7 @@ class IndexActionTest extends TestCase
         $expectedPaginationDefaultPageSize = null,
         $expectedSortOrders = [],
         $expectedSortDefaultOrder = null
-    ) {
+    ): void {
         Yii::$app->getRequest()->setBodyParams([
             'per-page' => 11,
             'sort' => '-test-sort'
diff --git a/tests/framework/rest/SerializerTest.php b/tests/framework/rest/SerializerTest.php
index 120bcfaa6a..69a67dadcb 100644
--- a/tests/framework/rest/SerializerTest.php
+++ b/tests/framework/rest/SerializerTest.php
@@ -8,6 +8,10 @@
 
 namespace yiiunit\framework\rest;
 
+use Yii;
+use JsonSerializable;
+use ReturnTypeWillChange;
+use yii\data\DataProviderInterface;
 use yii\base\Model;
 use yii\data\ArrayDataProvider;
 use yii\rest\Serializer;
@@ -33,7 +37,7 @@ class SerializerTest extends TestCase
         TestModel::$extraFields = [];
     }
 
-    public function testSerializeModelErrors()
+    public function testSerializeModelErrors(): void
     {
         $serializer = new Serializer();
         $model = new TestModel();
@@ -54,7 +58,7 @@ class SerializerTest extends TestCase
         ], $serializer->serialize($model));
     }
 
-    public function testSerializeModelData()
+    public function testSerializeModelData(): void
     {
         $serializer = new Serializer();
         $model = new TestModel();
@@ -79,7 +83,7 @@ class SerializerTest extends TestCase
         ], $serializer->serialize($model));
     }
 
-    public function testExpand()
+    public function testExpand(): void
     {
         $serializer = new Serializer();
         $model = new TestModel();
@@ -92,28 +96,28 @@ class SerializerTest extends TestCase
             'field2' => 2,
         ], $serializer->serialize($model));
 
-        \Yii::$app->request->setQueryParams(['expand' => 'extraField1']);
+        Yii::$app->request->setQueryParams(['expand' => 'extraField1']);
         $this->assertSame([
             'field1' => 'test',
             'field2' => 2,
             'extraField1' => 'testExtra',
         ], $serializer->serialize($model));
 
-        \Yii::$app->request->setQueryParams(['expand' => 'extraField1,extraField2']);
+        Yii::$app->request->setQueryParams(['expand' => 'extraField1,extraField2']);
         $this->assertSame([
             'field1' => 'test',
             'field2' => 2,
             'extraField1' => 'testExtra',
         ], $serializer->serialize($model));
 
-        \Yii::$app->request->setQueryParams(['expand' => 'field1,extraField2']);
+        Yii::$app->request->setQueryParams(['expand' => 'field1,extraField2']);
         $this->assertSame([
             'field1' => 'test',
             'field2' => 2,
         ], $serializer->serialize($model));
     }
 
-    public function testNestedExpand()
+    public function testNestedExpand(): void
     {
         $serializer = new Serializer();
         $model = new TestModel();
@@ -122,7 +126,7 @@ class SerializerTest extends TestCase
         TestModel::$extraFields = ['extraField3'];
         TestModel2::$extraFields = ['extraField4'];
 
-        \Yii::$app->request->setQueryParams(['expand' => 'extraField3.extraField4']);
+        Yii::$app->request->setQueryParams(['expand' => 'extraField3.extraField4']);
         $this->assertSame([
             'field1' => 'test',
             'field2' => 2,
@@ -134,7 +138,7 @@ class SerializerTest extends TestCase
         ], $serializer->serialize($model));
     }
 
-    public function testFields()
+    public function testFields(): void
     {
         $serializer = new Serializer();
         $model = new TestModel();
@@ -142,19 +146,19 @@ class SerializerTest extends TestCase
 
         TestModel::$extraFields = ['extraField3'];
 
-        \Yii::$app->request->setQueryParams([]);
+        Yii::$app->request->setQueryParams([]);
         $this->assertSame([
             'field1' => 'test',
             'field2' => 2,
         ], $serializer->serialize($model));
 
-        \Yii::$app->request->setQueryParams(['fields' => '*']);
+        Yii::$app->request->setQueryParams(['fields' => '*']);
         $this->assertSame([
             'field1' => 'test',
             'field2' => 2,
         ], $serializer->serialize($model));
 
-        \Yii::$app->request->setQueryParams(
+        Yii::$app->request->setQueryParams(
             [
                 'fields' => 'field1,extraField3.field3',
                 'expand' => 'extraField3.extraField4'
@@ -168,7 +172,7 @@ class SerializerTest extends TestCase
             ],
         ], $serializer->serialize($model));
 
-        \Yii::$app->request->setQueryParams(
+        Yii::$app->request->setQueryParams(
             [
                 'fields' => 'extraField3.*',
                 'expand' => 'extraField3',
@@ -181,7 +185,7 @@ class SerializerTest extends TestCase
             ],
         ], $serializer->serialize($model));
 
-        \Yii::$app->request->setQueryParams(
+        Yii::$app->request->setQueryParams(
             [
                 'fields' => 'extraField3.*',
                 'expand' => 'extraField3.extraField4'
@@ -200,7 +204,7 @@ class SerializerTest extends TestCase
             new TestModel2(),
         ];
 
-        \Yii::$app->request->setQueryParams(
+        Yii::$app->request->setQueryParams(
             [
                 'fields' => 'extraField3.*',
                 'expand' => 'extraField3',
@@ -219,7 +223,7 @@ class SerializerTest extends TestCase
             ],
         ], $serializer->serialize($model));
 
-        \Yii::$app->request->setQueryParams(
+        Yii::$app->request->setQueryParams(
             [
                 'fields' => '*,extraField3.*',
                 'expand' => 'extraField3',
@@ -240,7 +244,7 @@ class SerializerTest extends TestCase
             ],
         ], $serializer->serialize($model));
 
-        \Yii::$app->request->setQueryParams(
+        Yii::$app->request->setQueryParams(
             [
                 'fields' => 'extraField3.field3',
                 'expand' => 'extraField3',
@@ -257,24 +261,24 @@ class SerializerTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/12107
      */
-    public function testExpandInvalidInput()
+    public function testExpandInvalidInput(): void
     {
         $serializer = new Serializer();
         $model = new TestModel();
 
-        \Yii::$app->request->setQueryParams(['expand' => ['field1,extraField2']]);
+        Yii::$app->request->setQueryParams(['expand' => ['field1,extraField2']]);
         $this->assertSame([
             'field1' => 'test',
             'field2' => 2,
         ], $serializer->serialize($model));
 
-        \Yii::$app->request->setQueryParams(['fields' => ['field1,extraField2']]);
+        Yii::$app->request->setQueryParams(['fields' => ['field1,extraField2']]);
         $this->assertSame([
             'field1' => 'test',
             'field2' => 2,
         ], $serializer->serialize($model));
 
-        \Yii::$app->request->setQueryParams(['fields' => ['field1,extraField2'], 'expand' => ['field1,extraField2']]);
+        Yii::$app->request->setQueryParams(['fields' => ['field1,extraField2'], 'expand' => ['field1,extraField2']]);
         $this->assertSame([
             'field1' => 'test',
             'field2' => 2,
@@ -404,11 +408,11 @@ class SerializerTest extends TestCase
     /**
      * @dataProvider dataProviderSerializeDataProvider
      *
-     * @param \yii\data\DataProviderInterface $dataProvider
+     * @param DataProviderInterface $dataProvider
      * @param array $expectedResult
      * @param bool $saveKeys
      */
-    public function testSerializeDataProvider($dataProvider, $expectedResult, $saveKeys = false)
+    public function testSerializeDataProvider($dataProvider, $expectedResult, $saveKeys = false): void
     {
         $serializer = new Serializer();
         $serializer->preserveKeys = $saveKeys;
@@ -419,7 +423,7 @@ class SerializerTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/16334
      */
-    public function testSerializeJsonSerializable()
+    public function testSerializeJsonSerializable(): void
     {
         $serializer = new Serializer();
         $model3 = new TestModel3();
@@ -432,7 +436,7 @@ class SerializerTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/16334
      */
-    public function testSerializeArrayableWithJsonSerializableAttribute()
+    public function testSerializeArrayableWithJsonSerializableAttribute(): void
     {
         $serializer = new Serializer();
         $model = new TestModel5();
@@ -452,7 +456,7 @@ class SerializerTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/17886
      */
-    public function testSerializeArray()
+    public function testSerializeArray(): void
     {
         $serializer = new Serializer();
         $model1 = new TestModel();
@@ -518,7 +522,7 @@ class TestModel2 extends Model
     }
 }
 
-class TestModel3 extends Model implements \JsonSerializable
+class TestModel3 extends Model implements JsonSerializable
 {
     public static $fields = ['field3', 'field4'];
     public static $extraFields = [];
@@ -541,18 +545,18 @@ class TestModel3 extends Model implements \JsonSerializable
         return static::$extraFields;
     }
 
-    #[\ReturnTypeWillChange]
+    #[ReturnTypeWillChange]
     public function jsonSerialize()
     {
         return $this->getAttributes();
     }
 }
-class TestModel4 implements \JsonSerializable
+class TestModel4 implements JsonSerializable
 {
     public $field5 = 'test5';
     public $field6 = 'test6';
 
-    #[\ReturnTypeWillChange]
+    #[ReturnTypeWillChange]
     public function jsonSerialize()
     {
         return [
diff --git a/tests/framework/rest/UrlRuleTest.php b/tests/framework/rest/UrlRuleTest.php
index 4aeb78e872..5557a24660 100644
--- a/tests/framework/rest/UrlRuleTest.php
+++ b/tests/framework/rest/UrlRuleTest.php
@@ -27,7 +27,7 @@ class UrlRuleTest extends TestCase
         $this->mockApplication();
     }
 
-    public function testInitControllerNamePluralization()
+    public function testInitControllerNamePluralization(): void
     {
         $suites = $this->getTestsForControllerNamePluralization();
         foreach ($suites as $i => $suite) {
@@ -40,7 +40,7 @@ class UrlRuleTest extends TestCase
         }
     }
 
-    public function testParseRequest()
+    public function testParseRequest(): void
     {
         $manager = new UrlManager(['cache' => null]);
         $request = new Request(['hostInfo' => 'http://en.example.com', 'methodParam' => '_METHOD']);
@@ -359,7 +359,7 @@ class UrlRuleTest extends TestCase
      * @param array $ruleConfig
      * @param array $tests
      */
-    public function testCreateUrl($ruleConfig, $tests)
+    public function testCreateUrl($ruleConfig, $tests): void
     {
         foreach ($tests as $test) {
             list($params, $expected) = $test;
@@ -382,7 +382,7 @@ class UrlRuleTest extends TestCase
      * @param array $ruleConfig
      * @param array $tests
      */
-    public function testGetCreateUrlStatus($ruleConfig, $tests)
+    public function testGetCreateUrlStatus($ruleConfig, $tests): void
     {
         foreach ($tests as $test) {
             list($params, $expected, $status) = $test;
diff --git a/tests/framework/test/ActiveFixtureTest.php b/tests/framework/test/ActiveFixtureTest.php
index 1850623074..3b3d8c7934 100644
--- a/tests/framework/test/ActiveFixtureTest.php
+++ b/tests/framework/test/ActiveFixtureTest.php
@@ -37,7 +37,7 @@ class ActiveFixtureTest extends DatabaseTestCase
         parent::tearDown();
     }
 
-    public function testGetData()
+    public function testGetData(): void
     {
         $test = new CustomerDbTestCase();
         $test->setUp();
@@ -56,7 +56,7 @@ class ActiveFixtureTest extends DatabaseTestCase
         $test->tearDown();
     }
 
-    public function testGetModel()
+    public function testGetModel(): void
     {
         $test = new CustomerDbTestCase();
         $test->setUp();
@@ -74,7 +74,7 @@ class ActiveFixtureTest extends DatabaseTestCase
         $test->tearDown();
     }
 
-    public function testDataDirectory()
+    public function testDataDirectory(): void
     {
         $test = new CustomDirectoryDbTestCase();
 
@@ -87,7 +87,7 @@ class ActiveFixtureTest extends DatabaseTestCase
         $test->tearDown();
     }
 
-    public function testDataPath()
+    public function testDataPath(): void
     {
         $test = new DataPathDbTestCase();
 
@@ -100,7 +100,7 @@ class ActiveFixtureTest extends DatabaseTestCase
         $test->tearDown();
     }
 
-    public function testTruncate()
+    public function testTruncate(): void
     {
         $test = new TruncateTestCase();
 
@@ -113,7 +113,7 @@ class ActiveFixtureTest extends DatabaseTestCase
     /**
      * @see https://github.com/yiisoft/yii2/pull/14343
      */
-    public function testDifferentModelDb()
+    public function testDifferentModelDb(): void
     {
         $fixture = new DifferentDbFixture();
 
@@ -126,7 +126,7 @@ class ProfileFixture extends ActiveFixture
 {
     public $modelClass = 'yiiunit\data\ar\Profile';
 
-    public function beforeLoad()
+    public function beforeLoad(): void
     {
         if ($this->db->driverName === 'sqlsrv') {
             $this->db->createCommand()->truncateTable('profile')->execute();
@@ -157,7 +157,7 @@ class CustomerFixture extends ActiveFixture
         'yiiunit\framework\test\ProfileFixture',
     ];
 
-    public function beforeLoad()
+    public function beforeLoad(): void
     {
         if ($this->db->driverName === 'sqlsrv') {
             $this->db->createCommand()->truncateTable('customer')->execute();
@@ -173,7 +173,7 @@ class CustomDirectoryFixture extends ActiveFixture
 
     public $dataDirectory = '@app/framework/test/custom';
 
-    public function beforeLoad()
+    public function beforeLoad(): void
     {
         if ($this->db->driverName === 'sqlsrv') {
             $this->db->createCommand()->truncateTable('customer')->execute();
diff --git a/tests/framework/test/ArrayFixtureTest.php b/tests/framework/test/ArrayFixtureTest.php
index 9b2a3d14c8..8892472565 100644
--- a/tests/framework/test/ArrayFixtureTest.php
+++ b/tests/framework/test/ArrayFixtureTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\test;
 
+use yii\base\InvalidConfigException;
 use yii\test\ArrayFixture;
 use yiiunit\TestCase;
 
@@ -17,7 +18,7 @@ use yiiunit\TestCase;
 class ArrayFixtureTest extends TestCase
 {
     /**
-     * @var \yii\test\ArrayFixture
+     * @var ArrayFixture
      */
     private $_fixture;
 
@@ -27,7 +28,7 @@ class ArrayFixtureTest extends TestCase
         $this->_fixture = new ArrayFixture();
     }
 
-    public function testLoadUnloadParticularFile()
+    public function testLoadUnloadParticularFile(): void
     {
         $this->_fixture->dataFile = '@yiiunit/framework/test/data/array_fixture.php';
         $this->assertEmpty($this->_fixture->data, 'fixture data should be empty');
@@ -39,7 +40,7 @@ class ArrayFixtureTest extends TestCase
         $this->assertEquals('customer2@example.com', $this->_fixture['customer2']['email'], 'second fixture data should match');
     }
 
-    public function testNothingToLoad()
+    public function testNothingToLoad(): void
     {
         $this->_fixture->dataFile = false;
         $this->assertEmpty($this->_fixture->data, 'fixture data should be empty');
@@ -48,11 +49,11 @@ class ArrayFixtureTest extends TestCase
         $this->assertEmpty($this->_fixture->data, 'fixture data should not be loaded');
     }
 
-    public function testWrongDataFileException()
+    public function testWrongDataFileException(): void
     {
         $this->_fixture->dataFile = 'wrong/fixtures/data/path/alias';
 
-        $this->expectException(\yii\base\InvalidConfigException::class);
+        $this->expectException(InvalidConfigException::class);
 
         $this->_fixture->load();
     }
diff --git a/tests/framework/test/FixtureTest.php b/tests/framework/test/FixtureTest.php
index c2b4f4e686..e0a6d180ef 100644
--- a/tests/framework/test/FixtureTest.php
+++ b/tests/framework/test/FixtureTest.php
@@ -16,12 +16,12 @@ class Fixture1 extends Fixture
 {
     public $depends = ['yiiunit\framework\test\Fixture2'];
 
-    public function load()
+    public function load(): void
     {
         MyTestCase::$load .= '1';
     }
 
-    public function unload()
+    public function unload(): void
     {
         MyTestCase::$unload .= '1';
     }
@@ -31,12 +31,12 @@ class Fixture2 extends Fixture
 {
     public $depends = ['yiiunit\framework\test\Fixture3'];
 
-    public function load()
+    public function load(): void
     {
         MyTestCase::$load .= '2';
     }
 
-    public function unload()
+    public function unload(): void
     {
         MyTestCase::$unload .= '2';
     }
@@ -44,12 +44,12 @@ class Fixture2 extends Fixture
 
 class Fixture3 extends Fixture
 {
-    public function load()
+    public function load(): void
     {
         MyTestCase::$load .= '3';
     }
 
-    public function unload()
+    public function unload(): void
     {
         MyTestCase::$unload .= '3';
     }
@@ -59,12 +59,12 @@ class Fixture4 extends Fixture
 {
     public $depends = ['yiiunit\framework\test\Fixture5'];
 
-    public function load()
+    public function load(): void
     {
         MyTestCase::$load .= '4';
     }
 
-    public function unload()
+    public function unload(): void
     {
         MyTestCase::$unload .= '4';
     }
@@ -74,12 +74,12 @@ class Fixture5 extends Fixture
 {
     public $depends = ['yiiunit\framework\test\Fixture4'];
 
-    public function load()
+    public function load(): void
     {
         MyTestCase::$load .= '5';
     }
 
-    public function unload()
+    public function unload(): void
     {
         MyTestCase::$unload .= '5';
     }
@@ -172,7 +172,7 @@ class MyTestCase
  */
 class FixtureTest extends TestCase
 {
-    public function testDependencies()
+    public function testDependencies(): void
     {
         foreach ($this->getDependencyTests() as $scenario => $result) {
             $test = new MyTestCase();
@@ -184,7 +184,7 @@ class FixtureTest extends TestCase
         }
     }
 
-    public function testLoadSequence()
+    public function testLoadSequence(): void
     {
         foreach ($this->getLoadSequenceTests() as $scenario => $result) {
             $test = new MyTestCase();
diff --git a/tests/framework/validators/BooleanValidatorTest.php b/tests/framework/validators/BooleanValidatorTest.php
index 2eb547d013..f66e44b026 100644
--- a/tests/framework/validators/BooleanValidatorTest.php
+++ b/tests/framework/validators/BooleanValidatorTest.php
@@ -26,7 +26,7 @@ class BooleanValidatorTest extends TestCase
         $this->destroyApplication();
     }
 
-    public function testValidateValue()
+    public function testValidateValue(): void
     {
         $val = new BooleanValidator();
         $this->assertTrue($val->validate(true));
@@ -49,7 +49,7 @@ class BooleanValidatorTest extends TestCase
         $this->assertTrue($val->validate(false));
     }
 
-    public function testValidateAttributeAndError()
+    public function testValidateAttributeAndError(): void
     {
         $obj = new FakedValidationModel();
         $obj->attrA = true;
@@ -68,7 +68,7 @@ class BooleanValidatorTest extends TestCase
         $this->assertTrue($obj->hasErrors('attrD'));
     }
 
-    public function testErrorMessage()
+    public function testErrorMessage(): void
     {
         $validator = new BooleanValidator([
             'trueValue' => true,
diff --git a/tests/framework/validators/CompareValidatorTest.php b/tests/framework/validators/CompareValidatorTest.php
index 8fdb0292d6..62277e3acd 100644
--- a/tests/framework/validators/CompareValidatorTest.php
+++ b/tests/framework/validators/CompareValidatorTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\validators;
 
+use Exception;
 use yii\base\InvalidConfigException;
 use yii\validators\CompareValidator;
 use yiiunit\data\validators\models\FakedValidationModel;
@@ -26,14 +27,14 @@ class CompareValidatorTest extends TestCase
         $this->destroyApplication();
     }
 
-    public function testValidateValueException()
+    public function testValidateValueException(): void
     {
         $this->expectException('yii\base\InvalidConfigException');
         $val = new CompareValidator();
         $val->validate('val');
     }
 
-    public function testValidateValue()
+    public function testValidateValue(): void
     {
         $value = 18449;
         // default config
@@ -109,7 +110,7 @@ class CompareValidatorTest extends TestCase
         ];
     }
 
-    public function testValidateAttribute()
+    public function testValidateAttribute(): void
     {
         // invalid-array
         $val = new CompareValidator();
@@ -173,7 +174,7 @@ class CompareValidatorTest extends TestCase
         $this->assertFalse($model->hasErrors('attr_y'));
     }
 
-    public function testAttributeErrorMessages()
+    public function testAttributeErrorMessages(): void
     {
         $model = FakedValidationModel::createWithAttributes([
             'attr1' => 1,
@@ -218,7 +219,7 @@ class CompareValidatorTest extends TestCase
         ];
     }
 
-    public function testValidateAttributeOperators()
+    public function testValidateAttributeOperators(): void
     {
         $value = 55;
         foreach ($this->getOperationTestData($value) as $operator => $tests) {
@@ -232,7 +233,7 @@ class CompareValidatorTest extends TestCase
         }
     }
 
-    public function testEnsureMessageSetOnInit()
+    public function testEnsureMessageSetOnInit(): void
     {
         foreach ($this->getOperationTestData(1337) as $operator => $tests) {
             $val = new CompareValidator(['operator' => $operator]);
@@ -242,7 +243,7 @@ class CompareValidatorTest extends TestCase
             new CompareValidator(['operator' => '<>']);
         } catch (InvalidConfigException $e) {
             return;
-        } catch (\Exception $e) {
+        } catch (Exception $e) {
             $this->fail('InvalidConfigException expected' . get_class($e) . 'received');
 
             return;
diff --git a/tests/framework/validators/DateValidatorTest.php b/tests/framework/validators/DateValidatorTest.php
index 7e75a23ecb..78589e5bc1 100644
--- a/tests/framework/validators/DateValidatorTest.php
+++ b/tests/framework/validators/DateValidatorTest.php
@@ -37,7 +37,7 @@ class DateValidatorTest extends TestCase
         IntlTestHelper::resetIntlStatus();
     }
 
-    public function testEnsureMessageIsSet()
+    public function testEnsureMessageIsSet(): void
     {
         $val = new DateValidator();
         $this->assertTrue($val->message !== null && strlen($val->message) > 1);
@@ -47,7 +47,7 @@ class DateValidatorTest extends TestCase
      * @dataProvider provideTimezones
      * @param string $timezone
      */
-    public function testIntlValidateValue($timezone)
+    public function testIntlValidateValue($timezone): void
     {
         date_default_timezone_set($timezone);
         $this->testValidateValue($timezone);
@@ -87,7 +87,7 @@ class DateValidatorTest extends TestCase
      * @dataProvider provideTimezones
      * @param string $timezone
      */
-    public function testValidateValue($timezone)
+    public function testValidateValue($timezone): void
     {
         date_default_timezone_set($timezone);
 
@@ -130,7 +130,7 @@ class DateValidatorTest extends TestCase
      * @dataProvider provideTimezones
      * @param string $timezone
      */
-    public function testIntlValidateAttributePHPFormat($timezone)
+    public function testIntlValidateAttributePHPFormat($timezone): void
     {
         $this->testValidateAttributePHPFormat($timezone);
     }
@@ -139,7 +139,7 @@ class DateValidatorTest extends TestCase
      * @dataProvider provideTimezones
      * @param string $timezone
      */
-    public function testValidateAttributePHPFormat($timezone)
+    public function testValidateAttributePHPFormat($timezone): void
     {
         date_default_timezone_set($timezone);
 
@@ -176,7 +176,7 @@ class DateValidatorTest extends TestCase
      * @dataProvider provideTimezones
      * @param string $timezone
      */
-    public function testIntlValidateAttributeICUFormat($timezone)
+    public function testIntlValidateAttributeICUFormat($timezone): void
     {
         $this->testValidateAttributeICUFormat($timezone);
     }
@@ -185,7 +185,7 @@ class DateValidatorTest extends TestCase
      * @dataProvider provideTimezones
      * @param string $timezone
      */
-    public function testValidateAttributeICUFormat($timezone)
+    public function testValidateAttributeICUFormat($timezone): void
     {
         date_default_timezone_set($timezone);
 
@@ -223,7 +223,7 @@ class DateValidatorTest extends TestCase
         $this->assertTrue($model->hasErrors('attr_date'));
     }
 
-    public function testIntlMultibyteString()
+    public function testIntlMultibyteString(): void
     {
         $val = new DateValidator(['format' => 'dd MMM yyyy', 'locale' => 'de_DE']);
         $model = FakedValidationModel::createWithAttributes(['attr_date' => '12 Mai 2014']);
@@ -271,7 +271,7 @@ class DateValidatorTest extends TestCase
      * @param string $timezone
      * @param string $appTimezone
      */
-    public function testIntlTimestampAttributeFormat($format, $date, $expectedDate, $timezone, $appTimezone)
+    public function testIntlTimestampAttributeFormat($format, $date, $expectedDate, $timezone, $appTimezone): void
     {
         $this->testTimestampAttributeFormat($format, $date, $expectedDate, $timezone, $appTimezone);
     }
@@ -284,7 +284,7 @@ class DateValidatorTest extends TestCase
      * @param string $timezone
      * @param string $appTimezone
      */
-    public function testTimestampAttributeFormat($format, $date, $expectedDate, $timezone, $appTimezone)
+    public function testTimestampAttributeFormat($format, $date, $expectedDate, $timezone, $appTimezone): void
     {
         date_default_timezone_set($timezone);
 
@@ -302,7 +302,7 @@ class DateValidatorTest extends TestCase
      * @dataProvider provideTimezones
      * @param string $timezone
      */
-    public function testIntlValidationWithTime($timezone)
+    public function testIntlValidationWithTime($timezone): void
     {
         // prepare data for specific ICU version, see https://github.com/yiisoft/yii2/issues/15140
         switch (true) {
@@ -358,7 +358,7 @@ class DateValidatorTest extends TestCase
      * @dataProvider provideTimezones
      * @param string $timezone
      */
-    public function testValidationWithTime($timezone)
+    public function testValidationWithTime($timezone): void
     {
         date_default_timezone_set($timezone);
 
@@ -464,7 +464,7 @@ class DateValidatorTest extends TestCase
      * @dataProvider provideTimezones
      * @param string $timezone
      */
-    public function testIntlValidationWithTimeAndOutputTimeZone($timezone)
+    public function testIntlValidationWithTimeAndOutputTimeZone($timezone): void
     {
         $this->testValidationWithTime($timezone);
     }
@@ -473,7 +473,7 @@ class DateValidatorTest extends TestCase
      * @dataProvider provideTimezones
      * @param string $timezone
      */
-    public function testValidationWithTimeAndOutputTimeZone($timezone)
+    public function testValidationWithTimeAndOutputTimeZone($timezone): void
     {
         date_default_timezone_set($timezone);
 
@@ -536,7 +536,7 @@ class DateValidatorTest extends TestCase
      * @dataProvider provideTimezones
      * @param string $timezone
      */
-    public function testValidationWithoutTime($timezone)
+    public function testValidationWithoutTime($timezone): void
     {
         date_default_timezone_set($timezone);
 
@@ -884,17 +884,17 @@ class DateValidatorTest extends TestCase
      * @dataProvider provideTimezones
      * @param string $timezone
      */
-    public function testIntlValidationWithoutTime($timezone)
+    public function testIntlValidationWithoutTime($timezone): void
     {
         $this->testValidationWithoutTime($timezone);
     }
 
-    public function testIntlValidateRange()
+    public function testIntlValidateRange(): void
     {
         $this->testValidateValueRange();
     }
 
-    public function testValidateValueRange()
+    public function testValidateValueRange(): void
     {
         if (PHP_INT_SIZE == 8) { // this passes only on 64bit systems
             // intl parser allows 14 for yyyy pattern, see the following for more details:
@@ -928,7 +928,7 @@ class DateValidatorTest extends TestCase
         $this->assertFalse($val->validate('2000-01-02'), 'max +1 day is invalid');
     }
 
-    private function validateModelAttribute($validator, $date, $expected, $message = '')
+    private function validateModelAttribute($validator, $date, $expected, $message = ''): void
     {
         $model = new FakedValidationModel();
         $model->attr_date = $date;
@@ -940,12 +940,12 @@ class DateValidatorTest extends TestCase
         }
     }
 
-    public function testIntlValidateAttributeRange()
+    public function testIntlValidateAttributeRange(): void
     {
         $this->testValidateAttributeRange();
     }
 
-    public function testValidateAttributeRange()
+    public function testValidateAttributeRange(): void
     {
         if (PHP_INT_SIZE == 8) { // this passes only on 64bit systems
             // intl parser allows 14 for yyyy pattern, see the following for more details:
@@ -979,7 +979,7 @@ class DateValidatorTest extends TestCase
         $this->validateModelAttribute($val, '2000-01-02', false, 'max +1 day is invalid');
     }
 
-    public function testIntlValidateValueRangeOld()
+    public function testIntlValidateValueRangeOld(): void
     {
         if ($this->checkOldIcuBug()) {
             $this->markTestSkipped('ICU is too old.');
@@ -989,7 +989,7 @@ class DateValidatorTest extends TestCase
         $this->assertFalse($val->validate($date), "$date is too small");
     }
 
-    public function testIntlValidateAttributeRangeOld()
+    public function testIntlValidateAttributeRangeOld(): void
     {
         if ($this->checkOldIcuBug()) {
             $this->markTestSkipped('ICU is too old.');
@@ -1022,7 +1022,7 @@ class DateValidatorTest extends TestCase
     /**
      * @depends testValidateAttributePHPFormat
      */
-    public function testTimestampAttributeSkipValidation()
+    public function testTimestampAttributeSkipValidation(): void
     {
         // timestamp as integer
         $val = new DateValidator(['format' => 'php:Y/m/d', 'timestampAttribute' => 'attr_date']);
@@ -1059,7 +1059,7 @@ class DateValidatorTest extends TestCase
      * @param $date
      * @param $strictDateFormat
      */
-    public function testStrictDateFormatIntlFail($format, $date, $strictDateFormat)
+    public function testStrictDateFormatIntlFail($format, $date, $strictDateFormat): void
     {
         $this->mockApplication([
             'timeZone' => 'UTC',
@@ -1096,7 +1096,7 @@ class DateValidatorTest extends TestCase
      * @param $date
      * @param $strictDateFormat
      */
-    public function testStrictDateFormatIntlPass($format, $date, $strictDateFormat)
+    public function testStrictDateFormatIntlPass($format, $date, $strictDateFormat): void
     {
         $this->mockApplication([
             'timeZone' => 'UTC',
@@ -1128,7 +1128,7 @@ class DateValidatorTest extends TestCase
      * @param $date
      * @param $strictDateFormat
      */
-    public function testStrictDateFormatPhpFail($format, $date, $strictDateFormat)
+    public function testStrictDateFormatPhpFail($format, $date, $strictDateFormat): void
     {
         $this->mockApplication([
             'timeZone' => 'UTC',
@@ -1164,7 +1164,7 @@ class DateValidatorTest extends TestCase
      * @param $date
      * @param $strictDateFormat
      */
-    public function testStrictDateFormatPhpPass($format, $date, $strictDateFormat)
+    public function testStrictDateFormatPhpPass($format, $date, $strictDateFormat): void
     {
         $this->mockApplication([
             'timeZone' => 'UTC',
@@ -1191,7 +1191,7 @@ class DateValidatorTest extends TestCase
     /**
      * @depends testValidateAttributePHPFormat
      */
-    public function testTimestampAttributeOnEmpty()
+    public function testTimestampAttributeOnEmpty(): void
     {
         $validator = new DateValidator([
             'format' => 'php:Y/m/d',
@@ -1221,7 +1221,7 @@ class DateValidatorTest extends TestCase
      * Tests that DateValidator with format `php:U` does not truncate timestamp to date.
      * @see https://github.com/yiisoft/yii2/issues/15628
      */
-    public function testIssue15628()
+    public function testIssue15628(): void
     {
         $validator = new DateValidator(['format' => 'php:U', 'type' => DateValidator::TYPE_DATETIME, 'timestampAttribute' => 'attr_date']);
         $model = new FakedValidationModel();
diff --git a/tests/framework/validators/DefaultValueValidatorTest.php b/tests/framework/validators/DefaultValueValidatorTest.php
index 7d4b255213..d3b288a0cf 100644
--- a/tests/framework/validators/DefaultValueValidatorTest.php
+++ b/tests/framework/validators/DefaultValueValidatorTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\validators;
 
+use stdclass;
 use yii\validators\DefaultValueValidator;
 use yiiunit\TestCase;
 
@@ -24,11 +25,11 @@ class DefaultValueValidatorTest extends TestCase
         $this->destroyApplication();
     }
 
-    public function testValidateAttribute()
+    public function testValidateAttribute(): void
     {
         $val = new DefaultValueValidator();
         $val->value = 'test_value';
-        $obj = new \stdclass();
+        $obj = new stdclass();
         $obj->attrA = 'attrA';
         $obj->attrB = null;
         $obj->attrC = '';
diff --git a/tests/framework/validators/EachValidatorTest.php b/tests/framework/validators/EachValidatorTest.php
index e547099588..44bbf4a544 100644
--- a/tests/framework/validators/EachValidatorTest.php
+++ b/tests/framework/validators/EachValidatorTest.php
@@ -29,7 +29,7 @@ class EachValidatorTest extends TestCase
         $this->destroyApplication();
     }
 
-    public function testArrayFormat()
+    public function testArrayFormat(): void
     {
         $validator = new EachValidator(['rule' => ['required']]);
 
@@ -40,7 +40,7 @@ class EachValidatorTest extends TestCase
     /**
      * @depends testArrayFormat
      */
-    public function testValidate()
+    public function testValidate(): void
     {
         $validator = new EachValidator(['rule' => ['integer']]);
 
@@ -51,7 +51,7 @@ class EachValidatorTest extends TestCase
     /**
      * @depends testArrayFormat
      */
-    public function testFilter()
+    public function testFilter(): void
     {
         $model = FakedValidationModel::createWithAttributes([
             'attr_one' => [
@@ -66,7 +66,7 @@ class EachValidatorTest extends TestCase
     /**
      * @depends testValidate
      */
-    public function testAllowMessageFromRule()
+    public function testAllowMessageFromRule(): void
     {
         $model = FakedValidationModel::createWithAttributes([
             'attr_one' => [
@@ -88,7 +88,7 @@ class EachValidatorTest extends TestCase
     /**
      * @depends testValidate
      */
-    public function testCustomMessageValue()
+    public function testCustomMessageValue(): void
     {
         $model = FakedValidationModel::createWithAttributes([
             'attr_one' => [
@@ -112,7 +112,7 @@ class EachValidatorTest extends TestCase
      *
      * @depends testValidate
      */
-    public function testSkipOnEmpty()
+    public function testSkipOnEmpty(): void
     {
         $validator = new EachValidator(['rule' => ['integer', 'skipOnEmpty' => true]]);
         $this->assertTrue($validator->validate(['']));
@@ -140,7 +140,7 @@ class EachValidatorTest extends TestCase
      *
      * @depends testValidate
      */
-    public function testCompare()
+    public function testCompare(): void
     {
         $model = FakedValidationModel::createWithAttributes([
             'attr_one' => [
@@ -171,7 +171,7 @@ class EachValidatorTest extends TestCase
     /**
      * @depends testValidate
      */
-    public function testStopOnFirstError()
+    public function testStopOnFirstError(): void
     {
         $model = FakedValidationModel::createWithAttributes([
             'attr_one' => [
@@ -190,7 +190,7 @@ class EachValidatorTest extends TestCase
         $this->assertCount(2, $model->getErrors('attr_one'));
     }
 
-    public function testValidateArrayAccess()
+    public function testValidateArrayAccess(): void
     {
         $model = FakedValidationModel::createWithAttributes([
             'attr_array' => new ArrayAccessObject([1,2,3]),
@@ -213,7 +213,7 @@ class EachValidatorTest extends TestCase
      *
      * @requires PHP >= 7.4
      */
-    public function testTypedProperties()
+    public function testTypedProperties(): void
     {
         $model = new ValidatorTestTypedPropModel();
 
@@ -225,7 +225,7 @@ class EachValidatorTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/18011
      */
-    public function testErrorMessage()
+    public function testErrorMessage(): void
     {
         $model = new Speaker();
         $model->customLabel = ['invalid_ip'];
@@ -241,7 +241,7 @@ class EachValidatorTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/18051
      */
-    public function testCustomMethod()
+    public function testCustomMethod(): void
     {
         $model = new Speaker();
         $model->firstName = ['a', 'b'];
@@ -256,7 +256,7 @@ class EachValidatorTest extends TestCase
         $this->assertEquals(['a', 'b'], $model->firstName);
     }
 
-    public function testAnonymousMethod()
+    public function testAnonymousMethod(): void
     {
         $model = new ValidatorTestEachAndInlineMethodModel();
 
diff --git a/tests/framework/validators/EmailValidatorTest.php b/tests/framework/validators/EmailValidatorTest.php
index e148ad977e..13e0d6e4d4 100644
--- a/tests/framework/validators/EmailValidatorTest.php
+++ b/tests/framework/validators/EmailValidatorTest.php
@@ -25,7 +25,7 @@ class EmailValidatorTest extends TestCase
         $this->destroyApplication();
     }
 
-    public function testValidateValue()
+    public function testValidateValue(): void
     {
         $validator = new EmailValidator();
 
@@ -66,7 +66,7 @@ class EmailValidatorTest extends TestCase
         $this->assertFalse($validator->validate(['developer@yiiframework.com']));
     }
 
-    public function testValidateValueIdn()
+    public function testValidateValueIdn(): void
     {
         if (!function_exists('idn_to_ascii')) {
             $this->markTestSkipped('Intl extension required');
@@ -112,7 +112,7 @@ class EmailValidatorTest extends TestCase
         $this->assertFalse($validator->validate('Короткое имя <тест@это-доменное-имя.после-преобразования-в-idn.будет-содержать-больше-254-символов.бла-бла-бла-бла-бла-бла-бла-бла.бла-бла-бла-бла-бла-бла.бла-бла-бла-бла-бла-бла.бла-бла-бла-бла-бла-бла.com>'));
     }
 
-    public function testValidateValueMx()
+    public function testValidateValueMx(): void
     {
         $validator = new EmailValidator();
 
@@ -135,7 +135,7 @@ class EmailValidatorTest extends TestCase
         }
     }
 
-    public function testValidateAttribute()
+    public function testValidateAttribute(): void
     {
         $validator = new EmailValidator();
         $model = new FakedValidationModel();
@@ -178,7 +178,7 @@ class EmailValidatorTest extends TestCase
      * @dataProvider malformedAddressesProvider
      * @param string $value
      */
-    public function testMalformedAddressesIdnDisabled($value)
+    public function testMalformedAddressesIdnDisabled($value): void
     {
         $validator = new EmailValidator();
         $validator->enableIDN = false;
@@ -192,7 +192,7 @@ class EmailValidatorTest extends TestCase
      * @dataProvider malformedAddressesProvider
      * @param string $value
      */
-    public function testMalformedAddressesIdnEnabled($value)
+    public function testMalformedAddressesIdnEnabled($value): void
     {
         if (!function_exists('idn_to_ascii')) {
             $this->markTestSkipped('Intl extension required');
diff --git a/tests/framework/validators/ExistValidatorTest.php b/tests/framework/validators/ExistValidatorTest.php
index 1727c46b4f..74d5d47d8f 100644
--- a/tests/framework/validators/ExistValidatorTest.php
+++ b/tests/framework/validators/ExistValidatorTest.php
@@ -29,7 +29,7 @@ abstract class ExistValidatorTest extends DatabaseTestCase
         ActiveRecord::$db = $this->getConnection();
     }
 
-    public function testValidateValueExpectedException()
+    public function testValidateValueExpectedException(): void
     {
         try {
             $val = new ExistValidator();
@@ -50,7 +50,7 @@ abstract class ExistValidatorTest extends DatabaseTestCase
         }
     }
 
-    public function testValidateValue()
+    public function testValidateValue(): void
     {
         $val = new ExistValidator(['targetClass' => ValidatorTestRefModel::className(), 'targetAttribute' => 'id']);
         $this->assertTrue($val->validate(2));
@@ -59,7 +59,7 @@ abstract class ExistValidatorTest extends DatabaseTestCase
         $this->assertFalse($val->validate(['1']));
     }
 
-    public function testValidateAttribute()
+    public function testValidateAttribute(): void
     {
         // existing value on different table
         $val = new ExistValidator(['targetClass' => ValidatorTestMainModel::className(), 'targetAttribute' => 'id']);
@@ -136,7 +136,7 @@ abstract class ExistValidatorTest extends DatabaseTestCase
         $this->assertTrue($m->hasErrors('test_val'));
     }
 
-    public function testValidateCompositeKeys()
+    public function testValidateCompositeKeys(): void
     {
         $val = new ExistValidator([
             'targetClass' => OrderItem::className(),
@@ -182,7 +182,7 @@ abstract class ExistValidatorTest extends DatabaseTestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/14150
      */
-    public function testTargetTableWithAlias()
+    public function testTargetTableWithAlias(): void
     {
         $oldTableName = OrderItem::$tableName;
         OrderItem::$tableName = '{{%order_item}}';
@@ -203,7 +203,7 @@ abstract class ExistValidatorTest extends DatabaseTestCase
      * Test expresssion in targetAttribute.
      * @see https://github.com/yiisoft/yii2/issues/14304
      */
-    public function testExpresionInAttributeColumnName()
+    public function testExpresionInAttributeColumnName(): void
     {
         $val = new ExistValidator([
             'targetClass' => OrderItem::className(),
@@ -215,7 +215,7 @@ abstract class ExistValidatorTest extends DatabaseTestCase
         $this->assertFalse($m->hasErrors('id'));
     }
 
-    public function testTargetRelation()
+    public function testTargetRelation(): void
     {
         $val = new ExistValidator(['targetRelation' => 'references']);
 
@@ -228,7 +228,7 @@ abstract class ExistValidatorTest extends DatabaseTestCase
         $this->assertTrue($m->hasErrors('id'));
     }
 
-    public function testTargetRelationWithFilter()
+    public function testTargetRelationWithFilter(): void
     {
         $val = new ExistValidator(['targetRelation' => 'references', 'filter' => function ($query) {
             $query->andWhere(['a_field' => 'ref_to_2']);
@@ -245,7 +245,7 @@ abstract class ExistValidatorTest extends DatabaseTestCase
         $this->assertTrue($m->hasErrors('id'));
     }
 
-    public function testForceMaster()
+    public function testForceMaster(): void
     {
         $connection = $this->getConnectionWithInvalidSlave();
         ActiveRecord::$db = $connection;
@@ -271,7 +271,7 @@ abstract class ExistValidatorTest extends DatabaseTestCase
         ActiveRecord::$db = $this->getConnection();
     }
 
-    public function testSecondTargetAttributeWithError()
+    public function testSecondTargetAttributeWithError(): void
     {
         $validator = new ExistValidator(['targetAttribute' => ['email', 'name']]);
         $customer = new Customer();
diff --git a/tests/framework/validators/FileValidatorTest.php b/tests/framework/validators/FileValidatorTest.php
index dac2e98ccf..67ba98b659 100644
--- a/tests/framework/validators/FileValidatorTest.php
+++ b/tests/framework/validators/FileValidatorTest.php
@@ -28,7 +28,7 @@ class FileValidatorTest extends TestCase
         $this->mockApplication();
     }
 
-    public function testAssureMessagesSetOnInit()
+    public function testAssureMessagesSetOnInit(): void
     {
         $val = new FileValidator();
         foreach (['message', 'uploadRequired', 'tooMany', 'wrongExtension', 'tooBig', 'tooSmall', 'wrongMimeType'] as $attr) {
@@ -36,7 +36,7 @@ class FileValidatorTest extends TestCase
         }
     }
 
-    public function testTypeSplitOnInit()
+    public function testTypeSplitOnInit(): void
     {
         $val = new FileValidator(['extensions' => 'jpeg, jpg, gif']);
         $this->assertEquals(['jpeg', 'jpg', 'gif'], $val->extensions);
@@ -57,7 +57,7 @@ class FileValidatorTest extends TestCase
         $this->assertEquals(['jpeg', 'exe'], $val->extensions);
     }
 
-    public function testMimeTypeSplitOnInit()
+    public function testMimeTypeSplitOnInit(): void
     {
         $val = new FileValidator(['mimeTypes' => 'text/plain, image/png']);
         $this->assertEquals(['text/plain', 'image/png'], $val->mimeTypes);
@@ -78,7 +78,7 @@ class FileValidatorTest extends TestCase
         $this->assertEquals(['text/plain', 'image/png'], $val->mimeTypes);
     }
 
-    public function testGetSizeLimit()
+    public function testGetSizeLimit(): void
     {
         $size = min(
             StringHelper::convertIniSizeToBytes(ini_get('upload_max_filesize')),
@@ -97,7 +97,7 @@ class FileValidatorTest extends TestCase
         $this->assertSame($_POST['MAX_FILE_SIZE'], $val->getSizeLimit());
     }
 
-    public function testValidateAttributeMultiple()
+    public function testValidateAttributeMultiple(): void
     {
         $val = new FileValidator([
             'maxFiles' => 2,
@@ -228,7 +228,7 @@ class FileValidatorTest extends TestCase
         $this->assertFalse($m->validate());
     }
 
-    public function testValidateAttribute_minFilesGreaterThanOneMaxFilesUnlimited_notError()
+    public function testValidateAttribute_minFilesGreaterThanOneMaxFilesUnlimited_notError(): void
     {
         $validator = new FileValidator(['minFiles' => 2, 'maxFiles' => 0]);
         $model = FakedValidationModel::createWithAttributes(
@@ -255,7 +255,7 @@ class FileValidatorTest extends TestCase
         $this->assertFalse($model->hasErrors('attr_images'));
     }
 
-    public function testValidateAttribute_minFilesTwoMaxFilesFour_notError()
+    public function testValidateAttribute_minFilesTwoMaxFilesFour_notError(): void
     {
         $validator = new FileValidator(['minFiles' => 2, 'maxFiles' => 4]);
         $model = FakedValidationModel::createWithAttributes(
@@ -282,7 +282,7 @@ class FileValidatorTest extends TestCase
         $this->assertFalse($model->hasErrors('attr_images'));
     }
 
-    public function testValidateAttribute_minFilesTwoMaxFilesUnlimited_hasError()
+    public function testValidateAttribute_minFilesTwoMaxFilesUnlimited_hasError(): void
     {
         $validator = new FileValidator(['minFiles' => 2, 'maxFiles' => 0]);
         $model = FakedValidationModel::createWithAttributes(
@@ -310,7 +310,7 @@ class FileValidatorTest extends TestCase
     /**
      * https://github.com/yiisoft/yii2/issues/19855
      */
-    public function testValidateArrayAttributeWithMinMaxOneAndOneFile()
+    public function testValidateArrayAttributeWithMinMaxOneAndOneFile(): void
     {
         $validator = new FileValidator(['maxFiles' => 1, 'minFiles' => 0]);
         $files = $this->createTestFiles(
@@ -355,7 +355,7 @@ class FileValidatorTest extends TestCase
                 continue;
             }
             $name = isset($param['name']) ? $param['name'] : $rndString();
-            $tempName = \Yii::getAlias('@yiiunit/runtime/validators/file/tmp/') . $name;
+            $tempName = Yii::getAlias('@yiiunit/runtime/validators/file/tmp/') . $name;
             if (is_readable($tempName)) {
                 $size = filesize($tempName);
             } else {
@@ -395,7 +395,7 @@ class FileValidatorTest extends TestCase
      */
     protected function getRealTestFile($fileName)
     {
-        $filePath = \Yii::getAlias('@yiiunit/framework/validators/data/mimeType/') . $fileName;
+        $filePath = Yii::getAlias('@yiiunit/framework/validators/data/mimeType/') . $fileName;
 
         return new UploadedFile([
             'name' => $fileName,
@@ -406,7 +406,7 @@ class FileValidatorTest extends TestCase
         ]);
     }
 
-    public function testValidateAttribute()
+    public function testValidateAttribute(): void
     {
         // single File
         $val = new FileValidator();
@@ -452,7 +452,7 @@ class FileValidatorTest extends TestCase
         $this->assertSame(Yii::t('yii', 'File upload failed.'), current($m->getErrors('attr_err_part')));
     }
 
-    public function testValidateAttributeType()
+    public function testValidateAttributeType(): void
     {
         $val = new FileValidator([
             'extensions' => 'jpeg, jpg',
@@ -471,7 +471,7 @@ class FileValidatorTest extends TestCase
         $this->assertNotFalse(stripos(current($m->getErrors('attr_exe')), 'Only files with these extensions '));
     }
 
-    public function testValidateEmptyExtension()
+    public function testValidateEmptyExtension(): void
     {
         $val = new FileValidator([
             'extensions' => ['txt', ''],
@@ -492,7 +492,7 @@ class FileValidatorTest extends TestCase
         $this->assertFalse($m->hasErrors('attr_empty2'));
     }
 
-    public function testValidateAttributeDoubleType()
+    public function testValidateAttributeDoubleType(): void
     {
         $val = new FileValidator([
             'extensions' => 'tar.gz, tar.xz',
@@ -518,7 +518,7 @@ class FileValidatorTest extends TestCase
         $this->assertNotFalse(stripos(current($m->getErrors('attr_badtar')), 'Only files with these extensions '));
     }
 
-    public function testIssue11012()
+    public function testIssue11012(): void
     {
         $baseName = '飛兒樂團光茫';
         /** @var UploadedFile $file */
@@ -533,7 +533,7 @@ class FileValidatorTest extends TestCase
      * @param string $mask
      * @dataProvider validMimeTypes
      */
-    public function testValidateMimeTypeMaskValid($fileName, $mask)
+    public function testValidateMimeTypeMaskValid($fileName, $mask): void
     {
         $validator = new FileValidator(['mimeTypes' => $mask]);
         $file = $this->getRealTestFile($fileName);
@@ -545,7 +545,7 @@ class FileValidatorTest extends TestCase
      * @param string $mask
      * @dataProvider invalidMimeTypes
      */
-    public function testValidateMimeTypeMaskInvalid($fileName, $mask)
+    public function testValidateMimeTypeMaskInvalid($fileName, $mask): void
     {
         $validator = new FileValidator(['mimeTypes' => $mask]);
         $file = $this->getRealTestFile($fileName);
@@ -592,7 +592,7 @@ class FileValidatorTest extends TestCase
      * @param string|array $allowedExtensions
      * @dataProvider validMimeTypes
      */
-    public function testValidateFileByExtensionUsingMimeType($fileName, $_, $allowedExtensions)
+    public function testValidateFileByExtensionUsingMimeType($fileName, $_, $allowedExtensions): void
     {
         $validator = new FileValidator(['extensions' => (array) $allowedExtensions]);
         $file = $this->getRealTestFile($fileName);
@@ -606,7 +606,7 @@ class FileValidatorTest extends TestCase
      * @param string|array $allowedExtensions
      * @dataProvider invalidMimeTypes
      */
-    public function testValidateFileByExtensionUsingMimeTypeInvalid($fileName, $_, $allowedExtensions)
+    public function testValidateFileByExtensionUsingMimeTypeInvalid($fileName, $_, $allowedExtensions): void
     {
         $validator = new FileValidator(['extensions' => (array) $allowedExtensions]);
         $file = $this->getRealTestFile($fileName);
@@ -630,7 +630,7 @@ class FileValidatorTest extends TestCase
         );
     }
 
-    public function testValidateAttributeErrPartial()
+    public function testValidateAttributeErrPartial(): void
     {
         $m = $this->createModelForAttributeTest();
         $val = new FileValidator();
@@ -639,7 +639,7 @@ class FileValidatorTest extends TestCase
         $this->assertSame(Yii::t('yii', 'File upload failed.'), current($m->getErrors('attr_err_part')));
     }
 
-    public function testValidateAttributeErrCantWrite()
+    public function testValidateAttributeErrCantWrite(): void
     {
         $m = $this->createModelForAttributeTest();
         $val = new FileValidator();
@@ -648,7 +648,7 @@ class FileValidatorTest extends TestCase
         $this->assertSame(Yii::t('yii', 'File upload failed.'), current($m->getErrors('attr_err_write')));
     }
 
-    public function testValidateAttributeErrExtension()
+    public function testValidateAttributeErrExtension(): void
     {
         $m = $this->createModelForAttributeTest();
         $val = new FileValidator();
@@ -657,7 +657,7 @@ class FileValidatorTest extends TestCase
         $this->assertSame(Yii::t('yii', 'File upload failed.'), current($m->getErrors('attr_err_ext')));
     }
 
-    public function testValidateAttributeErrNoTmpDir()
+    public function testValidateAttributeErrNoTmpDir(): void
     {
         $m = $this->createModelForAttributeTest();
         $val = new FileValidator();
@@ -672,9 +672,9 @@ class FileValidatorTest extends TestCase
      * @param bool   $expected
      * @dataProvider mimeTypeCaseInsensitive
      */
-    public function testValidateMimeTypeCaseInsensitive($mask, $fileMimeType, $expected)
+    public function testValidateMimeTypeCaseInsensitive($mask, $fileMimeType, $expected): void
     {
-        $validator = $this->getMockBuilder(\yii\validators\FileValidator::class)
+        $validator = $this->getMockBuilder(FileValidator::class)
             ->onlyMethods(['getMimeTypeByFile'])
             ->getMock();
         $validator->method('getMimeTypeByFile')->willReturn($fileMimeType);
@@ -694,7 +694,7 @@ class FileValidatorTest extends TestCase
         ];
     }
 
-    public function testValidateTypedAttributeNoErrors()
+    public function testValidateTypedAttributeNoErrors(): void
     {
         if (version_compare(PHP_VERSION, '7.4', '<')) {
             $this->markTestSkipped('Requires typed properties');
@@ -719,7 +719,7 @@ class FileValidatorTest extends TestCase
         $this->assertFalse($model->hasErrors('multiple'));
     }
 
-    public function testValidateTypedAttributeExactMinNoErrors()
+    public function testValidateTypedAttributeExactMinNoErrors(): void
     {
         if (version_compare(PHP_VERSION, '7.4', '<')) {
             $this->markTestSkipped('Requires typed properties');
@@ -744,7 +744,7 @@ class FileValidatorTest extends TestCase
         $this->assertFalse($model->hasErrors('multiple'));
     }
 
-    public function testValidateTypedAttributeExactMaxNoErrors()
+    public function testValidateTypedAttributeExactMaxNoErrors(): void
     {
         if (version_compare(PHP_VERSION, '7.4', '<')) {
             $this->markTestSkipped('Requires typed properties');
@@ -769,7 +769,7 @@ class FileValidatorTest extends TestCase
         $this->assertFalse($model->hasErrors('multiple'));
     }
 
-    public function testValidateTypedAttributeMinError()
+    public function testValidateTypedAttributeMinError(): void
     {
         if (version_compare(PHP_VERSION, '7.4', '<')) {
             $this->markTestSkipped('Requires typed properties');
@@ -794,7 +794,7 @@ class FileValidatorTest extends TestCase
         $this->assertTrue($model->hasErrors('multiple'));
     }
 
-    public function testValidateTypedAttributeMaxError()
+    public function testValidateTypedAttributeMaxError(): void
     {
         if (version_compare(PHP_VERSION, '7.4', '<')) {
             $this->markTestSkipped('Requires typed properties');
diff --git a/tests/framework/validators/FilterValidatorTest.php b/tests/framework/validators/FilterValidatorTest.php
index f7589e2877..447d6b900b 100644
--- a/tests/framework/validators/FilterValidatorTest.php
+++ b/tests/framework/validators/FilterValidatorTest.php
@@ -24,13 +24,13 @@ class FilterValidatorTest extends TestCase
         $this->destroyApplication();
     }
 
-    public function testAssureExceptionOnInit()
+    public function testAssureExceptionOnInit(): void
     {
         $this->expectException('yii\base\InvalidConfigException');
         new FilterValidator();
     }
 
-    public function testValidateAttribute()
+    public function testValidateAttribute(): void
     {
         $m = FakedValidationModel::createWithAttributes([
                 'attr_one' => '  to be trimmed  ',
diff --git a/tests/framework/validators/IpValidatorTest.php b/tests/framework/validators/IpValidatorTest.php
index 4802b5f403..6276e62d1e 100644
--- a/tests/framework/validators/IpValidatorTest.php
+++ b/tests/framework/validators/IpValidatorTest.php
@@ -24,7 +24,7 @@ class IpValidatorTest extends TestCase
         $this->destroyApplication();
     }
 
-    public function testInitException()
+    public function testInitException(): void
     {
         $this->expectException('yii\base\InvalidConfigException');
         $this->expectExceptionMessage('Both IPv4 and IPv6 checks can not be disabled at the same time');
@@ -46,13 +46,13 @@ class IpValidatorTest extends TestCase
      * @param array $range
      * @param array $expectedRange
      */
-    public function testRangesSubstitution($range, $expectedRange)
+    public function testRangesSubstitution($range, $expectedRange): void
     {
         $validator = new IpValidator(['ranges' => $range]);
         $this->assertEquals($expectedRange, $validator->ranges);
     }
 
-    public function testValidateOrder()
+    public function testValidateOrder(): void
     {
         $validator = new IpValidator([
             'ranges' => ['10.0.0.1', '!10.0.0.0/8', '!babe::/8', 'any'],
@@ -74,7 +74,7 @@ class IpValidatorTest extends TestCase
      * @dataProvider provideBadIps
      * @param mixed $badIp
      */
-    public function testValidateValueNotAnIP($badIp)
+    public function testValidateValueNotAnIP($badIp): void
     {
         $validator = new IpValidator();
 
@@ -85,7 +85,7 @@ class IpValidatorTest extends TestCase
      * @dataProvider provideBadIps
      * @param mixed $badIp
      */
-    public function testValidateModelAttributeNotAnIP($badIp)
+    public function testValidateModelAttributeNotAnIP($badIp): void
     {
         $validator = new IpValidator();
         $model = new FakedValidationModel();
@@ -113,7 +113,7 @@ class IpValidatorTest extends TestCase
         $model->clearErrors();
     }
 
-    public function testValidateValueIPv4()
+    public function testValidateValueIPv4(): void
     {
         $validator = new IpValidator();
 
@@ -147,7 +147,7 @@ class IpValidatorTest extends TestCase
         $this->assertFalse($validator->validate('!!192.168.5.32/32'));
     }
 
-    public function testValidateValueIPv6()
+    public function testValidateValueIPv6(): void
     {
         $validator = new IpValidator();
 
@@ -182,7 +182,7 @@ class IpValidatorTest extends TestCase
         $this->assertFalse($validator->validate('!!2008:fa::0:1/64'));
     }
 
-    public function testValidateValueIPvBoth()
+    public function testValidateValueIPvBoth(): void
     {
         $validator = new IpValidator();
 
@@ -238,7 +238,7 @@ class IpValidatorTest extends TestCase
         $this->assertFalse($validator->validate('!!2008:fa::0:1/64'));
     }
 
-    public function testValidateRangeIPv4()
+    public function testValidateRangeIPv4(): void
     {
         $validator = new IpValidator([
             'ranges' => ['10.0.1.0/24'],
@@ -263,7 +263,7 @@ class IpValidatorTest extends TestCase
         $this->assertFalse($validator->validate('10.0.1.1/22'));
     }
 
-    public function testValidateRangeIPv6()
+    public function testValidateRangeIPv6(): void
     {
         $validator = new IpValidator([
             'ranges' => '2001:db0:1:1::/64',
@@ -282,7 +282,7 @@ class IpValidatorTest extends TestCase
         $this->assertTrue($validator->validate('2001:db0:1:2::7'));
     }
 
-    public function testValidateRangeIPvBoth()
+    public function testValidateRangeIPvBoth(): void
     {
         $validator = new IpValidator([
             'ranges' => '10.0.1.0/24',
@@ -311,7 +311,7 @@ class IpValidatorTest extends TestCase
         $this->assertFalse($validator->validate('10.0.1.1/22'));
     }
 
-    public function testValidateAttributeIPv4()
+    public function testValidateAttributeIPv4(): void
     {
         $validator = new IpValidator();
         $model = new FakedValidationModel();
@@ -345,7 +345,7 @@ class IpValidatorTest extends TestCase
         $this->assertEquals('8.8.8.8/32', $model->attr_ip);
     }
 
-    public function testValidateAttributeIPv6()
+    public function testValidateAttributeIPv6(): void
     {
         $validator = new IpValidator();
         $model = new FakedValidationModel();
diff --git a/tests/framework/validators/NumberValidatorTest.php b/tests/framework/validators/NumberValidatorTest.php
index 75c6e3a9d5..7b4e9330f7 100644
--- a/tests/framework/validators/NumberValidatorTest.php
+++ b/tests/framework/validators/NumberValidatorTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\validators;
 
+use stdClass;
 use yii\validators\NumberValidator;
 use yii\web\View;
 use yiiunit\data\validators\models\FakedValidationModel;
@@ -22,7 +23,7 @@ class NumberValidatorTest extends TestCase
     private $pointDecimalLocales = ['en_US.UTF-8', 'en_US.UTF8', 'en_US.utf-8', 'en_US.utf8', 'English_United States.1252'];
     private $oldLocale;
 
-    private function setCommaDecimalLocale()
+    private function setCommaDecimalLocale(): void
     {
         if ($this->oldLocale === false) {
             $this->markTestSkipped('Your platform does not support locales.');
@@ -33,7 +34,7 @@ class NumberValidatorTest extends TestCase
         }
     }
 
-    private function setPointDecimalLocale()
+    private function setPointDecimalLocale(): void
     {
         if ($this->oldLocale === false) {
             $this->markTestSkipped('Your platform does not support locales.');
@@ -44,7 +45,7 @@ class NumberValidatorTest extends TestCase
         }
     }
 
-    private function restoreLocale()
+    private function restoreLocale(): void
     {
         setlocale(LC_NUMERIC, $this->oldLocale);
     }
@@ -59,7 +60,7 @@ class NumberValidatorTest extends TestCase
         $this->destroyApplication();
     }
 
-    public function testEnsureMessageOnInit()
+    public function testEnsureMessageOnInit(): void
     {
         $val = new NumberValidator();
         $this->assertSame('{attribute} must be a number.', $val->message);
@@ -73,7 +74,7 @@ class NumberValidatorTest extends TestCase
         $this->assertSame('{attribute} must be no greater than {max}.', $val->tooBig);
     }
 
-    public function testValidateValueSimple()
+    public function testValidateValueSimple(): void
     {
         $val = new NumberValidator();
         $this->assertTrue($val->validate(20));
@@ -127,7 +128,7 @@ class NumberValidatorTest extends TestCase
         $this->assertSame('the input value must be an integer.', $error);
     }
 
-    public function testValidateValueArraySimple()
+    public function testValidateValueArraySimple(): void
     {
         $val = new NumberValidator();
         $this->assertFalse($val->validate([20], $error));
@@ -186,7 +187,7 @@ class NumberValidatorTest extends TestCase
         $this->assertSame('the input value must be an integer.', $error);
     }
 
-    public function testValidateValueAdvanced()
+    public function testValidateValueAdvanced(): void
     {
         $val = new NumberValidator();
         $this->assertTrue($val->validate('-1.23')); // signed float
@@ -218,7 +219,7 @@ class NumberValidatorTest extends TestCase
         $this->assertSame('the input value must be an integer.', $error);
     }
 
-    public function testValidateValueWithLocaleWhereDecimalPointIsComma()
+    public function testValidateValueWithLocaleWhereDecimalPointIsComma(): void
     {
         $val = new NumberValidator();
 
@@ -231,7 +232,7 @@ class NumberValidatorTest extends TestCase
         $this->restoreLocale();
     }
 
-    public function testValidateValueMin()
+    public function testValidateValueMin(): void
     {
         $val = new NumberValidator(['min' => 1]);
         $this->assertTrue($val->validate(1));
@@ -251,7 +252,7 @@ class NumberValidatorTest extends TestCase
         $this->assertSame('the input value must be an integer.', $error);
     }
 
-    public function testValidateValueMax()
+    public function testValidateValueMax(): void
     {
         $val = new NumberValidator(['max' => 1.25]);
         $this->assertTrue($val->validate(1));
@@ -269,7 +270,7 @@ class NumberValidatorTest extends TestCase
         $this->assertSame('the input value must be an integer.', $error);
     }
 
-    public function testValidateValueRange()
+    public function testValidateValueRange(): void
     {
         $val = new NumberValidator(['min' => -10, 'max' => 20]);
         $this->assertTrue($val->validate(0));
@@ -289,7 +290,7 @@ class NumberValidatorTest extends TestCase
         $this->assertSame('the input value must be an integer.', $error);
     }
 
-    public function testValidateAttribute()
+    public function testValidateAttribute(): void
     {
         $val = new NumberValidator();
         $model = new FakedValidationModel();
@@ -335,12 +336,12 @@ class NumberValidatorTest extends TestCase
 
         // @see https://github.com/yiisoft/yii2/issues/11672
         $model = new FakedValidationModel();
-        $model->attr_number = new \stdClass();
+        $model->attr_number = new stdClass();
         $val->validateAttribute($model, 'attr_number');
         $this->assertTrue($model->hasErrors('attr_number'));
     }
 
-    public function testValidateAttributeArray()
+    public function testValidateAttributeArray(): void
     {
         $val = new NumberValidator();
         $val->allowArray = true;
@@ -391,7 +392,7 @@ class NumberValidatorTest extends TestCase
 
         // @see https://github.com/yiisoft/yii2/issues/11672
         $model = new FakedValidationModel();
-        $model->attr_number = new \stdClass();
+        $model->attr_number = new stdClass();
         $val->validateAttribute($model, 'attr_number');
         $this->assertTrue($model->hasErrors('attr_number'));
         $this->assertSame('attr_number must be a number.', $model->getFirstError('attr_number'));
@@ -444,13 +445,13 @@ class NumberValidatorTest extends TestCase
 
         // @see https://github.com/yiisoft/yii2/issues/11672
         $model = new FakedValidationModel();
-        $model->attr_number = new \stdClass();
+        $model->attr_number = new stdClass();
         $val->validateAttribute($model, 'attr_number');
         $this->assertTrue($model->hasErrors('attr_number'));
         $this->assertSame('attr_number must be a number.', $model->getFirstError('attr_number'));
     }
 
-    public function testValidateAttributeWithLocaleWhereDecimalPointIsComma()
+    public function testValidateAttributeWithLocaleWhereDecimalPointIsComma(): void
     {
         $val = new NumberValidator();
         $model = new FakedValidationModel();
@@ -467,7 +468,7 @@ class NumberValidatorTest extends TestCase
         $this->restoreLocale();
     }
 
-    public function testEnsureCustomMessageIsSetOnValidateAttributeGeneral()
+    public function testEnsureCustomMessageIsSetOnValidateAttributeGeneral(): void
     {
         $val = new NumberValidator(['message' => '{attribute} is not integer.']);
         $model = new FakedValidationModel();
@@ -479,7 +480,7 @@ class NumberValidatorTest extends TestCase
         $this->assertSame('attr_number is not integer.', $msgs[0]);
     }
 
-    public function testEnsureCustomMessageIsSetOnValidateAttributeMin()
+    public function testEnsureCustomMessageIsSetOnValidateAttributeMin(): void
     {
         $val = new NumberValidator([
             'tooSmall' => '{attribute} is too small.',
@@ -494,7 +495,7 @@ class NumberValidatorTest extends TestCase
         $this->assertSame('attr_number is too small.', $msgs[0]);
     }
 
-    public function testEnsureCustomMessageIsSetOnValidateAttributeMax()
+    public function testEnsureCustomMessageIsSetOnValidateAttributeMax(): void
     {
         $val = new NumberValidator([
             'tooBig' => '{attribute} is too big.',
@@ -512,7 +513,7 @@ class NumberValidatorTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/3118
      */
-    public function testClientValidateComparison()
+    public function testClientValidateComparison(): void
     {
         $val = new NumberValidator([
             'min' => 5,
@@ -551,14 +552,14 @@ class NumberValidatorTest extends TestCase
         $this->assertStringContainsString('"max":13.37', $js);
     }
 
-    public function testValidateObject()
+    public function testValidateObject(): void
     {
         $val = new NumberValidator();
-        $value = new \stdClass();
+        $value = new stdClass();
         $this->assertFalse($val->validate($value));
     }
 
-    public function testValidateResource()
+    public function testValidateResource(): void
     {
         $val = new NumberValidator();
         $fp = fopen('php://stdin', 'r');
@@ -576,7 +577,7 @@ class NumberValidatorTest extends TestCase
         }
     }
 
-    public function testValidateToString()
+    public function testValidateToString(): void
     {
         $val = new NumberValidator();
         $object = new TestClass('10');
@@ -591,7 +592,7 @@ class NumberValidatorTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/18544
      */
-    public function testNotTrimmedStrings()
+    public function testNotTrimmedStrings(): void
     {
         $val = new NumberValidator(['integerOnly' => true]);
         $this->assertFalse($val->validate(' 1 '));
diff --git a/tests/framework/validators/RangeValidatorTest.php b/tests/framework/validators/RangeValidatorTest.php
index ac46f07066..439fc4ed83 100644
--- a/tests/framework/validators/RangeValidatorTest.php
+++ b/tests/framework/validators/RangeValidatorTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\validators;
 
+use ArrayObject;
 use yii\validators\RangeValidator;
 use yiiunit\data\validators\models\FakedValidationModel;
 use yiiunit\TestCase;
@@ -25,20 +26,20 @@ class RangeValidatorTest extends TestCase
         $this->destroyApplication();
     }
 
-    public function testInitException()
+    public function testInitException(): void
     {
         $this->expectException('yii\base\InvalidConfigException');
         $this->expectExceptionMessage('The "range" property must be set.');
         new RangeValidator(['range' => 'not an array']);
     }
 
-    public function testAssureMessageSetOnInit()
+    public function testAssureMessageSetOnInit(): void
     {
         $val = new RangeValidator(['range' => []]);
         $this->assertIsString($val->message);
     }
 
-    public function testValidateValue()
+    public function testValidateValue(): void
     {
         $val = new RangeValidator(['range' => range(1, 10, 1)]);
         $this->assertTrue($val->validate(1));
@@ -50,7 +51,7 @@ class RangeValidatorTest extends TestCase
         $this->assertTrue($val->validate('5'));
     }
 
-    public function testValidateValueEmpty()
+    public function testValidateValueEmpty(): void
     {
         $val = new RangeValidator(['range' => range(10, 20, 1), 'skipOnEmpty' => false]);
         $this->assertFalse($val->validate(null)); //row RangeValidatorTest.php:101
@@ -61,7 +62,7 @@ class RangeValidatorTest extends TestCase
         $this->assertTrue($val->validate([]));
     }
 
-    public function testValidateArrayValue()
+    public function testValidateArrayValue(): void
     {
         $val = new RangeValidator(['range' => range(1, 10, 1)]);
         $val->allowArray = true;
@@ -72,7 +73,7 @@ class RangeValidatorTest extends TestCase
         $this->assertTrue($val->validate(['1', '2', '3', 4, 5, 6]));
     }
 
-    public function testValidateValueStrict()
+    public function testValidateValueStrict(): void
     {
         $val = new RangeValidator(['range' => range(1, 10, 1), 'strict' => true]);
         $this->assertTrue($val->validate(1));
@@ -83,7 +84,7 @@ class RangeValidatorTest extends TestCase
         $this->assertFalse($val->validate('5.5'));
     }
 
-    public function testValidateArrayValueStrict()
+    public function testValidateArrayValueStrict(): void
     {
         $val = new RangeValidator(['range' => range(1, 10, 1), 'strict' => true]);
         $val->allowArray = true;
@@ -91,7 +92,7 @@ class RangeValidatorTest extends TestCase
         $this->assertFalse($val->validate(['1', '2', '3', 4, 5, 6]));
     }
 
-    public function testValidateValueNot()
+    public function testValidateValueNot(): void
     {
         $val = new RangeValidator(['range' => range(1, 10, 1), 'not' => true]);
         $this->assertFalse($val->validate(1));
@@ -103,7 +104,7 @@ class RangeValidatorTest extends TestCase
         $this->assertFalse($val->validate('5'));
     }
 
-    public function testValidateAttribute()
+    public function testValidateAttribute(): void
     {
         $val = new RangeValidator(['range' => range(1, 10, 1)]);
         $m = FakedValidationModel::createWithAttributes(['attr_r1' => 5, 'attr_r2' => 999]);
@@ -115,7 +116,7 @@ class RangeValidatorTest extends TestCase
         $this->assertNotFalse(stripos($err[0], 'attr_r2'));
     }
 
-    public function testValidateSubsetArrayable()
+    public function testValidateSubsetArrayable(): void
     {
         // Test in array, values are arrays. IE: ['a'] in [['a'], ['b']]
         $val = new RangeValidator([
@@ -136,12 +137,12 @@ class RangeValidatorTest extends TestCase
             'range' => ['a', 'b', 'c'],
             'allowArray' => true,
         ]);
-        $this->assertTrue($val->validate(new \ArrayObject(['a', 'b'])));
+        $this->assertTrue($val->validate(new ArrayObject(['a', 'b'])));
 
 
         // Test range as ArrayObject.
         $val = new RangeValidator([
-            'range' => new \ArrayObject(['a', 'b']),
+            'range' => new ArrayObject(['a', 'b']),
             'allowArray' => false,
         ]);
         $this->assertTrue($val->validate('a'));
diff --git a/tests/framework/validators/RegularExpressionValidatorTest.php b/tests/framework/validators/RegularExpressionValidatorTest.php
index d18f03284a..84cb9e0aa1 100644
--- a/tests/framework/validators/RegularExpressionValidatorTest.php
+++ b/tests/framework/validators/RegularExpressionValidatorTest.php
@@ -25,7 +25,7 @@ class RegularExpressionValidatorTest extends TestCase
         $this->destroyApplication();
     }
 
-    public function testValidateValue()
+    public function testValidateValue(): void
     {
         $val = new RegularExpressionValidator(['pattern' => '/^[a-zA-Z0-9](\.)?([^\/]*)$/m']);
         $this->assertTrue($val->validate('b.4'));
@@ -37,7 +37,7 @@ class RegularExpressionValidatorTest extends TestCase
         $this->assertFalse($val->validate(['a', 'b']));
     }
 
-    public function testValidateAttribute()
+    public function testValidateAttribute(): void
     {
         $val = new RegularExpressionValidator(['pattern' => '/^[a-zA-Z0-9](\.)?([^\/]*)$/m']);
         $m = FakedValidationModel::createWithAttributes(['attr_reg1' => 'b.4']);
@@ -48,13 +48,13 @@ class RegularExpressionValidatorTest extends TestCase
         $this->assertTrue($m->hasErrors('attr_reg1'));
     }
 
-    public function testMessageSetOnInit()
+    public function testMessageSetOnInit(): void
     {
         $val = new RegularExpressionValidator(['pattern' => '/^[a-zA-Z0-9](\.)?([^\/]*)$/m']);
         $this->assertIsString($val->message);
     }
 
-    public function testInitException()
+    public function testInitException(): void
     {
         $this->expectException('yii\base\InvalidConfigException');
         $val = new RegularExpressionValidator();
diff --git a/tests/framework/validators/RequiredValidatorTest.php b/tests/framework/validators/RequiredValidatorTest.php
index e554991dc7..8034d0a9aa 100644
--- a/tests/framework/validators/RequiredValidatorTest.php
+++ b/tests/framework/validators/RequiredValidatorTest.php
@@ -26,7 +26,7 @@ class RequiredValidatorTest extends TestCase
         $this->destroyApplication();
     }
 
-    public function testValidateValueWithDefaults()
+    public function testValidateValueWithDefaults(): void
     {
         $val = new RequiredValidator();
         $this->assertFalse($val->validate(null));
@@ -35,7 +35,7 @@ class RequiredValidatorTest extends TestCase
         $this->assertTrue($val->validate(['with', 'elements']));
     }
 
-    public function testValidateValueWithValue()
+    public function testValidateValueWithValue(): void
     {
         $val = new RequiredValidator(['requiredValue' => 55]);
         $this->assertTrue($val->validate(55));
@@ -50,7 +50,7 @@ class RequiredValidatorTest extends TestCase
         $this->assertFalse($val->validate(true));
     }
 
-    public function testValidateAttribute()
+    public function testValidateAttribute(): void
     {
         // empty req-value
         $val = new RequiredValidator();
@@ -69,7 +69,7 @@ class RequiredValidatorTest extends TestCase
         $this->assertFalse($m->hasErrors('attr_val'));
     }
 
-    public function testErrorClientMessage()
+    public function testErrorClientMessage(): void
     {
         $validator = new RequiredValidator(['message' => '<strong>error</strong> for {attribute}']);
 
diff --git a/tests/framework/validators/StringValidatorTest.php b/tests/framework/validators/StringValidatorTest.php
index 15913f1bc6..11e2c1a5ce 100644
--- a/tests/framework/validators/StringValidatorTest.php
+++ b/tests/framework/validators/StringValidatorTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\validators;
 
+use stdClass;
 use yii\validators\StringValidator;
 use yiiunit\data\validators\models\FakedValidationModel;
 use yiiunit\TestCase;
@@ -25,7 +26,7 @@ class StringValidatorTest extends TestCase
         $this->destroyApplication();
     }
 
-    public function testValidateValue()
+    public function testValidateValue(): void
     {
         $val = new StringValidator();
         $this->assertFalse($val->validate(['not a string']));
@@ -34,7 +35,7 @@ class StringValidatorTest extends TestCase
         $this->assertFalse($val->validate(false));
     }
 
-    public function testValidateValueLength()
+    public function testValidateValueLength(): void
     {
         $val = new StringValidator(['length' => 25]);
         $this->assertTrue($val->validate(str_repeat('x', 25)));
@@ -59,7 +60,7 @@ class StringValidatorTest extends TestCase
         $this->assertFalse($val->validate(str_repeat('x', 30)));
     }
 
-    public function testValidateValueMinMax()
+    public function testValidateValueMinMax(): void
     {
         $val = new StringValidator(['min' => 10]);
         $this->assertTrue($val->validate(str_repeat('x', 10)));
@@ -73,7 +74,7 @@ class StringValidatorTest extends TestCase
         $this->assertFalse($val->validate(str_repeat('b', 25)));
     }
 
-    public function testValidateAttribute()
+    public function testValidateAttribute(): void
     {
         $val = new StringValidator();
         $model = new FakedValidationModel();
@@ -110,7 +111,7 @@ class StringValidatorTest extends TestCase
         $this->assertTrue($model->hasErrors('attr_str'));
     }
 
-    public function testEnsureMessagesOnInit()
+    public function testEnsureMessagesOnInit(): void
     {
         $val = new StringValidator(['min' => 1, 'max' => 2]);
         $this->assertIsString($val->message);
@@ -118,7 +119,7 @@ class StringValidatorTest extends TestCase
         $this->assertIsString($val->tooShort);
     }
 
-    public function testCustomErrorMessageInValidateAttribute()
+    public function testCustomErrorMessageInValidateAttribute(): void
     {
         $val = new StringValidator([
             'min' => 5,
@@ -135,7 +136,7 @@ class StringValidatorTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/13327
      */
-    public function testValidateValueInNonStrictMode()
+    public function testValidateValueInNonStrictMode(): void
     {
         $val = new StringValidator();
         $val->strict = false;
@@ -145,7 +146,7 @@ class StringValidatorTest extends TestCase
 
         // non-scalar
         $this->assertFalse($val->validate(['array']));
-        $this->assertFalse($val->validate(new \stdClass()));
+        $this->assertFalse($val->validate(new stdClass()));
         $this->assertFalse($val->validate(null));
 
         // bool
diff --git a/tests/framework/validators/UniqueValidatorTest.php b/tests/framework/validators/UniqueValidatorTest.php
index 459cca9afa..b204daeacb 100644
--- a/tests/framework/validators/UniqueValidatorTest.php
+++ b/tests/framework/validators/UniqueValidatorTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\validators;
 
+use Exception;
 use Yii;
 use yii\validators\UniqueValidator;
 use yiiunit\data\ar\ActiveRecord;
@@ -32,13 +33,13 @@ abstract class UniqueValidatorTest extends DatabaseTestCase
         $this->destroyApplication();
     }
 
-    public function testAssureMessageSetOnInit()
+    public function testAssureMessageSetOnInit(): void
     {
         $val = new UniqueValidator();
         $this->assertIsString($val->message);
     }
 
-    public function testCustomMessage()
+    public function testCustomMessage(): void
     {
         // single attribute
         $customError = 'Custom message for Id with value "1"';
@@ -74,7 +75,7 @@ abstract class UniqueValidatorTest extends DatabaseTestCase
         $this->assertEquals($customError, $model->getFirstError('order_id'));
     }
 
-    public function testValidateInvalidAttribute()
+    public function testValidateInvalidAttribute(): void
     {
         $validator = new UniqueValidator();
         $messageError = Yii::t('yii', '{attribute} is invalid.', ['attribute' => 'Name']);
@@ -94,7 +95,7 @@ abstract class UniqueValidatorTest extends DatabaseTestCase
         $this->assertEquals($messageError, $customerModel->getFirstError('name'));
     }
 
-    public function testValidateAttributeDefault()
+    public function testValidateAttributeDefault(): void
     {
         $val = new UniqueValidator();
         $m = ValidatorTestMainModel::find()->one();
@@ -126,7 +127,7 @@ abstract class UniqueValidatorTest extends DatabaseTestCase
         $this->assertTrue($m->hasErrors('attr_arr'));
     }
 
-    public function testValidateAttributeOfNonARModel()
+    public function testValidateAttributeOfNonARModel(): void
     {
         $val = new UniqueValidator(['targetClass' => ValidatorTestRefModel::className(), 'targetAttribute' => 'ref']);
         $m = FakedValidationModel::createWithAttributes(['attr_1' => 5, 'attr_2' => 1313]);
@@ -136,7 +137,7 @@ abstract class UniqueValidatorTest extends DatabaseTestCase
         $this->assertFalse($m->hasErrors('attr_2'));
     }
 
-    public function testValidateNonDatabaseAttribute()
+    public function testValidateNonDatabaseAttribute(): void
     {
         $val = new UniqueValidator(['targetClass' => ValidatorTestRefModel::className(), 'targetAttribute' => 'ref']);
         /** @var ValidatorTestMainModel $m */
@@ -149,7 +150,7 @@ abstract class UniqueValidatorTest extends DatabaseTestCase
         $this->assertTrue($m->hasErrors('testMainVal'));
     }
 
-    public function testValidateAttributeAttributeNotInTableException()
+    public function testValidateAttributeAttributeNotInTableException(): void
     {
         $this->expectException('yii\db\Exception');
         $val = new UniqueValidator();
@@ -157,7 +158,7 @@ abstract class UniqueValidatorTest extends DatabaseTestCase
         $val->validateAttribute($m, 'testMainVal');
     }
 
-    public function testValidateCompositeKeys()
+    public function testValidateCompositeKeys(): void
     {
         $val = new UniqueValidator([
             'targetClass' => OrderItem::className(),
@@ -211,7 +212,7 @@ abstract class UniqueValidatorTest extends DatabaseTestCase
         $this->assertFalse($m->hasErrors('id'));
     }
 
-    public function testValidateTargetClass()
+    public function testValidateTargetClass(): void
     {
         // Check whether "Description" and "name" aren't equal
         $val = new UniqueValidator([
@@ -240,7 +241,7 @@ abstract class UniqueValidatorTest extends DatabaseTestCase
         $this->assertTrue($m->hasErrors('description'));
     }
 
-    public function testValidateScopeNamespaceTargetClassForNewClass()
+    public function testValidateScopeNamespaceTargetClassForNewClass(): void
     {
         $validator = new UniqueValidator();
 
@@ -260,7 +261,7 @@ abstract class UniqueValidatorTest extends DatabaseTestCase
         $this->assertTrue($profileModel->hasErrors('description'));
     }
 
-    public function testValidateScopeNamespaceTargetClass()
+    public function testValidateScopeNamespaceTargetClass(): void
     {
         $validator = new UniqueValidator();
 
@@ -280,7 +281,7 @@ abstract class UniqueValidatorTest extends DatabaseTestCase
         $this->assertFalse($profileModel->hasErrors('description'));
     }
 
-    public function testValidateEmptyAttributeInStringField()
+    public function testValidateEmptyAttributeInStringField(): void
     {
         ValidatorTestMainModel::deleteAll();
 
@@ -302,7 +303,7 @@ abstract class UniqueValidatorTest extends DatabaseTestCase
         $this->assertTrue($m->hasErrors('field1'));
     }
 
-    public function testValidateEmptyAttributeInIntField()
+    public function testValidateEmptyAttributeInIntField(): void
     {
         ValidatorTestRefModel::deleteAll();
 
@@ -324,7 +325,7 @@ abstract class UniqueValidatorTest extends DatabaseTestCase
         $this->assertTrue($m->hasErrors('ref'));
     }
 
-    public function testPrepareParams()
+    public function testPrepareParams(): void
     {
         $model = new FakedValidationModel();
         $model->val_attr_a = 'test value a';
@@ -361,7 +362,7 @@ abstract class UniqueValidatorTest extends DatabaseTestCase
         $this->assertEquals($expected, $result);
     }
 
-    public function testGetTargetClassWithFilledTargetClassProperty()
+    public function testGetTargetClassWithFilledTargetClassProperty(): void
     {
         $validator = new UniqueValidator(['targetClass' => Profile::className()]);
         $model = new FakedValidationModel();
@@ -370,7 +371,7 @@ abstract class UniqueValidatorTest extends DatabaseTestCase
         $this->assertEquals(Profile::className(), $actualTargetClass);
     }
 
-    public function testGetTargetClassWithNotFilledTargetClassProperty()
+    public function testGetTargetClassWithNotFilledTargetClassProperty(): void
     {
         $validator = new UniqueValidator();
         $model = new FakedValidationModel();
@@ -379,7 +380,7 @@ abstract class UniqueValidatorTest extends DatabaseTestCase
         $this->assertEquals(FakedValidationModel::className(), $actualTargetClass);
     }
 
-    public function testPrepareQuery()
+    public function testPrepareQuery(): void
     {
         $schema = $this->getConnection()->schema;
 
@@ -410,7 +411,7 @@ abstract class UniqueValidatorTest extends DatabaseTestCase
      * Test ambiguous column name in select clause.
      * @see https://github.com/yiisoft/yii2/issues/14042
      */
-    public function testAmbiguousColumnName()
+    public function testAmbiguousColumnName(): void
     {
         $validator = new UniqueValidator([
             'filter' => function ($query) {
@@ -429,7 +430,7 @@ abstract class UniqueValidatorTest extends DatabaseTestCase
      * Test expression in targetAttribute.
      * @see https://github.com/yiisoft/yii2/issues/14304
      */
-    public function testExpressionInAttributeColumnName()
+    public function testExpressionInAttributeColumnName(): void
     {
         $validator = new UniqueValidator([
             'targetAttribute' => [
@@ -449,7 +450,7 @@ abstract class UniqueValidatorTest extends DatabaseTestCase
      * Test validating a class with default scope
      * @see https://github.com/yiisoft/yii2/issues/14484
     */
-    public function testFindModelWith()
+    public function testFindModelWith(): void
     {
         $validator = new UniqueValidator([
             'targetAttribute' => ['status', 'profile_id']
@@ -458,7 +459,7 @@ abstract class UniqueValidatorTest extends DatabaseTestCase
         try {
             $validator->validateAttribute($model, 'email');
             $this->assertTrue(true);
-        } catch (\Exception $exception) {
+        } catch (Exception $exception) {
             $this->fail('Query is crashed because "with" relation cannot be loaded');
         }
     }
@@ -467,7 +468,7 @@ abstract class UniqueValidatorTest extends DatabaseTestCase
      * Test join with doesn't attempt to eager load joinWith relations
      * @see https://github.com/yiisoft/yii2/issues/17389
      */
-    public function testFindModelJoinWith()
+    public function testFindModelJoinWith(): void
     {
         $validator = new UniqueValidator([
             'targetAttribute' => ['status', 'profile_id'],
@@ -476,12 +477,12 @@ abstract class UniqueValidatorTest extends DatabaseTestCase
         try {
             $validator->validateAttribute($model, 'email');
             $this->assertTrue(true);
-        } catch (\Exception $exception) {
+        } catch (Exception $exception) {
             $this->fail('Query is crashed because "joinWith" relation cannot be loaded');
         }
     }
 
-    public function testForceMaster()
+    public function testForceMaster(): void
     {
         $connection = $this->getConnectionWithInvalidSlave();
         ActiveRecord::$db = $connection;
@@ -507,7 +508,7 @@ abstract class UniqueValidatorTest extends DatabaseTestCase
         ActiveRecord::$db = $this->getConnection();
     }
 
-    public function testSecondTargetAttributeWithError()
+    public function testSecondTargetAttributeWithError(): void
     {
         $validator = new UniqueValidator(['targetAttribute' => ['email', 'name']]);
         $customer = new Customer();
diff --git a/tests/framework/validators/UrlValidatorTest.php b/tests/framework/validators/UrlValidatorTest.php
index 06480a41a4..ec6ff71141 100644
--- a/tests/framework/validators/UrlValidatorTest.php
+++ b/tests/framework/validators/UrlValidatorTest.php
@@ -25,7 +25,7 @@ class UrlValidatorTest extends TestCase
         $this->destroyApplication();
     }
 
-    public function testValidateValue()
+    public function testValidateValue(): void
     {
         $val = new UrlValidator();
         $this->assertFalse($val->validate('google.de'));
@@ -56,20 +56,20 @@ class UrlValidatorTest extends TestCase
         $this->assertFalse($val->validate('http://äüö?=!"§$%&/()=}][{³²€.edu'));
     }
 
-    public function testValidateValueWithDefaultScheme()
+    public function testValidateValueWithDefaultScheme(): void
     {
         $val = new UrlValidator(['defaultScheme' => 'https']);
         $this->assertTrue($val->validate('yiiframework.com'));
         $this->assertTrue($val->validate('http://yiiframework.com'));
     }
 
-    public function testValidateValueWithoutScheme()
+    public function testValidateValueWithoutScheme(): void
     {
         $val = new UrlValidator(['pattern' => '/(([A-Z0-9][A-Z0-9_-]*)(\.[A-Z0-9][A-Z0-9_-]*)+)/i']);
         $this->assertTrue($val->validate('yiiframework.com'));
     }
 
-    public function testValidateWithCustomScheme()
+    public function testValidateWithCustomScheme(): void
     {
         $val = new UrlValidator([
             'validSchemes' => ['http', 'https', 'ftp', 'ftps'],
@@ -84,7 +84,7 @@ class UrlValidatorTest extends TestCase
         $this->assertFalse($val->validate('//yiiframework.com'));
     }
 
-    public function testValidateWithIdn()
+    public function testValidateWithIdn(): void
     {
         if (!function_exists('idn_to_ascii')) {
             $this->markTestSkipped('intl package required');
@@ -99,14 +99,14 @@ class UrlValidatorTest extends TestCase
         $this->assertTrue($val->validate('http://xn--zcack7ayc9a.de'));
     }
 
-    public function testValidateLength()
+    public function testValidateLength(): void
     {
         $url = 'http://' . str_pad('base', 2000, 'url') . '.de';
         $val = new UrlValidator();
         $this->assertFalse($val->validate($url));
     }
 
-    public function testValidateAttributeAndError()
+    public function testValidateAttributeAndError(): void
     {
         $obj = new FakedValidationModel();
         $obj->attr_url = 'http://google.de';
diff --git a/tests/framework/validators/ValidatorTest.php b/tests/framework/validators/ValidatorTest.php
index 1e986b2dd2..733634f18d 100644
--- a/tests/framework/validators/ValidatorTest.php
+++ b/tests/framework/validators/ValidatorTest.php
@@ -8,6 +8,8 @@
 
 namespace yiiunit\framework\validators;
 
+use stdClass;
+use yii\base\View;
 use yii\base\DynamicModel;
 use yii\validators\BooleanValidator;
 use yii\validators\InlineValidator;
@@ -43,7 +45,7 @@ class ValidatorTest extends TestCase
         return FakedValidationModel::createWithAttributes($attributes);
     }
 
-    public function testCreateValidator()
+    public function testCreateValidator(): void
     {
         $model = FakedValidationModel::createWithAttributes(['attr_test1' => 'abc', 'attr_test2' => '2013']);
         /** @var NumberValidator $numberVal */
@@ -79,7 +81,7 @@ class ValidatorTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/14370
      */
-    public function testCreateBuiltInValidatorWithSameNameFunction()
+    public function testCreateBuiltInValidatorWithSameNameFunction(): void
     {
         $model = new ValidatorTestFunctionModel();
 
@@ -88,7 +90,7 @@ class ValidatorTest extends TestCase
         $this->assertInstanceOf(RequiredValidator::className(), $validator);
     }
 
-    public function testValidateAttributes()
+    public function testValidateAttributes(): void
     {
         $val = new TestValidator(['attributes' => ['attr_runMe1', 'attr_runMe2']]);
         $model = $this->getTestModel();
@@ -98,7 +100,7 @@ class ValidatorTest extends TestCase
         $this->assertFalse($val->isAttributeValidated('attr_skip'));
     }
 
-    public function testValidateWithAttributeIntersect()
+    public function testValidateWithAttributeIntersect(): void
     {
         $val = new TestValidator(['attributes' => ['attr_runMe1', 'attr_runMe2']]);
         $model = $this->getTestModel();
@@ -108,7 +110,7 @@ class ValidatorTest extends TestCase
         $this->assertFalse($val->isAttributeValidated('attr_skip'));
     }
 
-    public function testValidateWithEmptyAttributes()
+    public function testValidateWithEmptyAttributes(): void
     {
         $val = new TestValidator();
         $model = $this->getTestModel();
@@ -122,7 +124,7 @@ class ValidatorTest extends TestCase
         $this->assertFalse($val->isAttributeValidated('attr_skip'));
     }
 
-    public function testValidateWithError()
+    public function testValidateWithError(): void
     {
         $val = new TestValidator(['attributes' => ['attr_runMe1', 'attr_runMe2'], 'skipOnError' => false]);
         $model = $this->getTestModel();
@@ -152,7 +154,7 @@ class ValidatorTest extends TestCase
         $this->assertEquals(0, $val->countAttributeValidations('attr_skip'));
     }
 
-    public function testValidateWithEmpty()
+    public function testValidateWithEmpty(): void
     {
         $model = $this->getTestModel(['attr_empty1' => '', 'attr_empty2' => ' ']);
         $attributes = ['attr_runMe1', 'attr_runMe2', 'attr_empty1', 'attr_empty2'];
@@ -179,7 +181,7 @@ class ValidatorTest extends TestCase
         $this->assertTrue($validator->isAttributeValidated('attr_empty1'));
     }
 
-    public function testIsEmpty()
+    public function testIsEmpty(): void
     {
         $val = new TestValidator();
         $this->assertTrue($val->isEmpty(null));
@@ -187,11 +189,11 @@ class ValidatorTest extends TestCase
         $this->assertTrue($val->isEmpty(''));
         $this->assertFalse($val->isEmpty(5));
         $this->assertFalse($val->isEmpty(0));
-        $this->assertFalse($val->isEmpty(new \stdClass()));
+        $this->assertFalse($val->isEmpty(new stdClass()));
         $this->assertFalse($val->isEmpty('  '));
     }
 
-    public function testValidateValue()
+    public function testValidateValue(): void
     {
         $this->expectException('yii\base\NotSupportedException');
         $this->expectExceptionMessage(TestValidator::className() . ' does not support validateValue().');
@@ -199,7 +201,7 @@ class ValidatorTest extends TestCase
         $val->validate('abc');
     }
 
-    public function testValidateAttribute()
+    public function testValidateAttribute(): void
     {
         // Access to validator in inline validation (https://github.com/yiisoft/yii2/issues/6242)
 
@@ -216,9 +218,9 @@ class ValidatorTest extends TestCase
         $this->assertInstanceOf(InlineValidator::className(), $args[2]);
     }
 
-    public function testClientValidateAttribute()
+    public function testClientValidateAttribute(): void
     {
-        $view = new \yii\base\View();
+        $view = new View();
         $val = new TestValidator();
         $this->assertNull(
             $val->clientValidateAttribute($this->getTestModel(), 'attr_runMe1', $view)
@@ -237,7 +239,7 @@ class ValidatorTest extends TestCase
         $this->assertInstanceOf(InlineValidator::className(), $args[2]);
     }
 
-    public function testIsActive()
+    public function testIsActive(): void
     {
         $val = new TestValidator();
         $this->assertTrue($val->isActive('scenA'));
@@ -251,7 +253,7 @@ class ValidatorTest extends TestCase
         $this->assertTrue($val->isActive('scenC'));
     }
 
-    public function testAddError()
+    public function testAddError(): void
     {
         $val = new TestValidator();
         $m = $this->getTestModel(['attr_msg_val' => 'abc']);
@@ -268,7 +270,7 @@ class ValidatorTest extends TestCase
         $this->assertEquals('attr_msg_val::abc::param_value', $errors[0]);
     }
 
-    public function testGetAttributeNames()
+    public function testGetAttributeNames(): void
     {
         $validator = new TestValidator();
         $validator->attributes = ['id', 'name', '!email'];
@@ -278,7 +280,7 @@ class ValidatorTest extends TestCase
     /**
      * @depends  testGetAttributeNames
      */
-    public function testGetActiveValidatorsForSafeAttributes()
+    public function testGetActiveValidatorsForSafeAttributes(): void
     {
         $model = $this->getTestModel();
         $validators = $model->getActiveValidators('safe_attr');
@@ -297,7 +299,7 @@ class ValidatorTest extends TestCase
      * @see https://github.com/yiisoft/yii2/issues/13979
      * @see https://github.com/yiisoft/yii2/pull/14413
      */
-    public function testAttributeNamesDynamic()
+    public function testAttributeNamesDynamic(): void
     {
         $model = new DynamicModel(['email1' => 'invalid', 'email2' => 'invalid']);
         $validator = new TestValidator();
@@ -316,7 +318,7 @@ class ValidatorTest extends TestCase
      * @see https://github.com/yiisoft/yii2/issues/17233
      * @see https://github.com/yiisoft/yii2/pull/17234
      */
-    public function testScalarAttributeNames()
+    public function testScalarAttributeNames(): void
     {
         $model = new DynamicModel();
         $model->defineAttribute(1);
diff --git a/tests/framework/web/AssetBundleTest.php b/tests/framework/web/AssetBundleTest.php
index ca102fdca1..dd19f7be05 100644
--- a/tests/framework/web/AssetBundleTest.php
+++ b/tests/framework/web/AssetBundleTest.php
@@ -8,6 +8,9 @@
 
 namespace yiiunit\framework\web;
 
+use yiiunit\TestCase;
+use Exception;
+use yii\base\InvalidConfigException;
 use Yii;
 use yii\helpers\FileHelper;
 use yii\web\AssetBundle;
@@ -17,7 +20,7 @@ use yii\web\View;
 /**
  * @group web
  */
-class AssetBundleTest extends \yiiunit\TestCase
+class AssetBundleTest extends TestCase
 {
     protected function setUp(): void
     {
@@ -33,7 +36,7 @@ class AssetBundleTest extends \yiiunit\TestCase
         // clean up assets directory
         $handle = opendir($dir = Yii::getAlias('@testAssetsPath'));
         if ($handle === false) {
-            throw new \Exception("Unable to open directory: $dir");
+            throw new Exception("Unable to open directory: $dir");
         }
         while (($file = readdir($handle)) !== false) {
             if ($file === '.' || $file === '..' || $file === '.gitignore') {
@@ -68,7 +71,7 @@ class AssetBundleTest extends \yiiunit\TestCase
         return $view;
     }
 
-    public function testSourcesPublish()
+    public function testSourcesPublish(): void
     {
         $view = $this->getView();
         $am = $view->assetManager;
@@ -81,7 +84,7 @@ class AssetBundleTest extends \yiiunit\TestCase
         $this->sourcesPublish_VerifyFiles('js', $bundle);
     }
 
-    private function sourcesPublish_VerifyFiles($type, $bundle)
+    private function sourcesPublish_VerifyFiles($type, $bundle): void
     {
         foreach ($bundle->$type as $filename) {
             $publishedFile = $bundle->basePath . DIRECTORY_SEPARATOR . $filename;
@@ -92,13 +95,13 @@ class AssetBundleTest extends \yiiunit\TestCase
         $this->assertTrue(is_dir($bundle->basePath . DIRECTORY_SEPARATOR . $type));
     }
 
-    public function testSourcesPublishedBySymlink()
+    public function testSourcesPublishedBySymlink(): void
     {
         $view = $this->getView(['linkAssets' => true]);
         $this->verifySourcesPublishedBySymlink($view);
     }
 
-    public function testSourcesPublishedBySymlink_Issue9333()
+    public function testSourcesPublishedBySymlink_Issue9333(): void
     {
         $view = $this->getView([
             'linkAssets' => true,
@@ -110,7 +113,7 @@ class AssetBundleTest extends \yiiunit\TestCase
         $this->assertTrue(is_dir(dirname($bundle->basePath)));
     }
 
-    public function testSourcesPublish_AssetManagerBeforeCopy()
+    public function testSourcesPublish_AssetManagerBeforeCopy(): void
     {
         $view = $this->getView([
             'beforeCopy' => function ($from, $to) {
@@ -129,7 +132,7 @@ class AssetBundleTest extends \yiiunit\TestCase
         }
     }
 
-    public function testSourcesPublish_AssetBeforeCopy()
+    public function testSourcesPublish_AssetBeforeCopy(): void
     {
         $view = $this->getView();
         $am = $view->assetManager;
@@ -149,7 +152,7 @@ class AssetBundleTest extends \yiiunit\TestCase
         }
     }
 
-    public function testSourcesPublish_publishOptions_Only()
+    public function testSourcesPublish_publishOptions_Only(): void
     {
         $view = $this->getView();
         $am = $view->assetManager;
@@ -174,7 +177,7 @@ class AssetBundleTest extends \yiiunit\TestCase
         $this->assertTrue(is_dir($bundle->basePath));
     }
 
-    public function testBasePathIsWritableOnPublish()
+    public function testBasePathIsWritableOnPublish(): void
     {
         Yii::setAlias('@testReadOnlyAssetPath', '@webroot/readOnlyAssets');
         $path = Yii::getAlias('@testReadOnlyAssetPath');
@@ -190,7 +193,7 @@ class AssetBundleTest extends \yiiunit\TestCase
         $view = $this->getView(['basePath' => '@testReadOnlyAssetPath']);
         $bundle = new TestSourceAsset();
 
-        $this->expectException(\yii\base\InvalidConfigException::class);
+        $this->expectException(InvalidConfigException::class);
         $this->expectExceptionMessage('The directory is not writable by the Web process');
 
         $bundle->publish($view->getAssetManager());
@@ -223,7 +226,7 @@ class AssetBundleTest extends \yiiunit\TestCase
         return $bundle;
     }
 
-    public function testRegister()
+    public function testRegister(): void
     {
         $view = $this->getView();
 
@@ -239,7 +242,7 @@ EOF;
         $this->assertEquals($expected, $view->renderFile('@yiiunit/data/views/rawlayout.php'));
     }
 
-    public function testSimpleDependency()
+    public function testSimpleDependency(): void
     {
         $view = $this->getView();
 
@@ -277,7 +280,7 @@ EOF;
      * @param int $pos
      * @param bool $jqAlreadyRegistered
      */
-    public function testPositionDependency($pos, $jqAlreadyRegistered)
+    public function testPositionDependency($pos, $jqAlreadyRegistered): void
     {
         $view = $this->getView();
 
@@ -348,7 +351,7 @@ EOF;
      * @param int $pos
      * @param bool $jqAlreadyRegistered
      */
-    public function testPositionDependencyConflict($pos, $jqAlreadyRegistered)
+    public function testPositionDependencyConflict($pos, $jqAlreadyRegistered): void
     {
         $view = $this->getView();
 
@@ -371,13 +374,13 @@ EOF;
         TestAssetBundle::register($view);
     }
 
-    public function testCircularDependency()
+    public function testCircularDependency(): void
     {
         $this->expectException('yii\\base\\InvalidConfigException');
         TestAssetCircleA::register($this->getView());
     }
 
-    public function testDuplicateAssetFile()
+    public function testDuplicateAssetFile(): void
     {
         $view = $this->getView();
 
@@ -395,7 +398,7 @@ EOF;
         $this->assertEquals($expected, $view->renderFile('@yiiunit/data/views/rawlayout.php'));
     }
 
-    public function testPerFileOptions()
+    public function testPerFileOptions(): void
     {
         $view = $this->getView();
 
@@ -522,7 +525,7 @@ EOF;
      * @param string $expected
      * @param string|null $webAlias
      */
-    public function testRegisterFileAppendTimestamp($type, $path, $appendTimestamp, $expected, $webAlias = null)
+    public function testRegisterFileAppendTimestamp($type, $path, $appendTimestamp, $expected, $webAlias = null): void
     {
         $originalAlias = Yii::getAlias('@web');
         if ($webAlias === null) {
@@ -538,7 +541,7 @@ EOF;
         Yii::setAlias('@web', $originalAlias);
     }
 
-    public function testCustomFilePublishWithTimestamp()
+    public function testCustomFilePublishWithTimestamp(): void
     {
         $path = Yii::getAlias('@webroot');
 
@@ -560,7 +563,7 @@ EOF;
     /**
      * @see https://github.com/yiisoft/yii2/issues/18529
      */
-    public function testNonRelativeAssetWebPathWithTimestamp()
+    public function testNonRelativeAssetWebPathWithTimestamp(): void
     {
         Yii::setAlias('@webroot', '@yiiunit/data/web/assetSources/');
 
diff --git a/tests/framework/web/AssetConverterTest.php b/tests/framework/web/AssetConverterTest.php
index d790534c92..9824f56621 100644
--- a/tests/framework/web/AssetConverterTest.php
+++ b/tests/framework/web/AssetConverterTest.php
@@ -8,13 +8,15 @@
 
 namespace yiiunit\framework\web;
 
+use yiiunit\TestCase;
+use Yii;
 use yii\helpers\FileHelper;
 use yii\web\AssetConverter;
 
 /**
  * @group web
  */
-class AssetConverterTest extends \yiiunit\TestCase
+class AssetConverterTest extends TestCase
 {
     /**
      * @var string temporary files path
@@ -25,7 +27,7 @@ class AssetConverterTest extends \yiiunit\TestCase
     {
         parent::setUp();
         $this->mockApplication();
-        $this->tmpPath = \Yii::$app->runtimePath . '/assetConverterTest_' . getmypid();
+        $this->tmpPath = Yii::$app->runtimePath . '/assetConverterTest_' . getmypid();
         if (!is_dir($this->tmpPath)) {
             mkdir($this->tmpPath, 0777, true);
         }
@@ -41,7 +43,7 @@ class AssetConverterTest extends \yiiunit\TestCase
 
     // Tests :
 
-    public function testConvert()
+    public function testConvert(): void
     {
         $tmpPath = $this->tmpPath;
         file_put_contents(
@@ -65,7 +67,7 @@ EOF
     /**
      * @depends testConvert
      */
-    public function testForceConvert()
+    public function testForceConvert(): void
     {
         $tmpPath = $this->tmpPath;
         file_put_contents(
diff --git a/tests/framework/web/ControllerTest.php b/tests/framework/web/ControllerTest.php
index 81132a7bfa..8b611e5d60 100644
--- a/tests/framework/web/ControllerTest.php
+++ b/tests/framework/web/ControllerTest.php
@@ -8,6 +8,10 @@
 
 namespace yiiunit\framework\web;
 
+use yii\web\Application;
+use yiiunit\framework\web\stubs\ModelBindingStub;
+use yii\base\Module;
+use yii\data\ArrayDataProvider;
 use RuntimeException;
 use Yii;
 use yii\base\InlineAction;
@@ -31,7 +35,7 @@ class ControllerTest extends TestCase
         parent::setUp();
 
         $this->mockWebApplication();
-        $this->controller = new FakeController('fake', new \yii\web\Application([
+        $this->controller = new FakeController('fake', new Application([
             'id' => 'app',
             'basePath' => __DIR__,
             'components' => [
@@ -46,7 +50,7 @@ class ControllerTest extends TestCase
         Yii::$app->controller = $this->controller;
     }
 
-    public function testBindActionParams()
+    public function testBindActionParams(): void
     {
         $aksi1 = new InlineAction('aksi1', $this->controller, 'actionAksi1');
 
@@ -61,10 +65,10 @@ class ControllerTest extends TestCase
         $this->assertEquals('available', $other);
     }
 
-    public function testNullableInjectedActionParams()
+    public function testNullableInjectedActionParams(): void
     {
         // Use the PHP71 controller for this test
-        $this->controller = new FakePhp71Controller('fake', new \yii\web\Application([
+        $this->controller = new FakePhp71Controller('fake', new Application([
             'id' => 'app',
             'basePath' => __DIR__,
 
@@ -84,15 +88,15 @@ class ControllerTest extends TestCase
         $this->assertNull($args[1]);
     }
 
-    public function testModelBindingHttpException()
+    public function testModelBindingHttpException(): void
     {
-        $this->controller = new FakePhp71Controller('fake', new \yii\web\Application([
+        $this->controller = new FakePhp71Controller('fake', new Application([
             'id' => 'app',
             'basePath' => __DIR__,
             'container' => [
                 'definitions' => [
-                    \yiiunit\framework\web\stubs\ModelBindingStub::className() => [
-                        \yiiunit\framework\web\stubs\ModelBindingStub::className(),
+                    ModelBindingStub::className() => [
+                        ModelBindingStub::className(),
                         'build',
                     ],
                 ],
@@ -113,10 +117,10 @@ class ControllerTest extends TestCase
         $this->controller->bindActionParams($injectionAction, []);
     }
 
-    public function testInjectionContainerException()
+    public function testInjectionContainerException(): void
     {
         // Use the PHP71 controller for this test
-        $this->controller = new FakePhp71Controller('fake', new \yii\web\Application([
+        $this->controller = new FakePhp71Controller('fake', new Application([
             'id' => 'app',
             'basePath' => __DIR__,
 
@@ -133,7 +137,7 @@ class ControllerTest extends TestCase
         $injectionAction = new InlineAction('injection', $this->controller, 'actionInjection');
         $params = ['between' => 'test', 'after' => 'another', 'before' => 'test'];
         Yii::$container->set(VendorImage::className(), function () {
-            throw new \RuntimeException('uh oh');
+            throw new RuntimeException('uh oh');
         });
 
         $this->expectException(get_class(new RuntimeException()));
@@ -141,10 +145,10 @@ class ControllerTest extends TestCase
         $this->controller->bindActionParams($injectionAction, $params);
     }
 
-    public function testUnknownInjection()
+    public function testUnknownInjection(): void
     {
         // Use the PHP71 controller for this test
-        $this->controller = new FakePhp71Controller('fake', new \yii\web\Application([
+        $this->controller = new FakePhp71Controller('fake', new Application([
             'id' => 'app',
             'basePath' => __DIR__,
             'components' => [
@@ -165,10 +169,10 @@ class ControllerTest extends TestCase
         $this->controller->bindActionParams($injectionAction, $params);
     }
 
-    public function testInjectedActionParams()
+    public function testInjectedActionParams(): void
     {
         // Use the PHP71 controller for this test
-        $this->controller = new FakePhp71Controller('fake', new \yii\web\Application([
+        $this->controller = new FakePhp71Controller('fake', new Application([
             'id' => 'app',
             'basePath' => __DIR__,
             'components' => [
@@ -195,9 +199,9 @@ class ControllerTest extends TestCase
         $this->assertEquals($params['after'], $args[5]);
     }
 
-    public function testInjectedActionParamsFromModule()
+    public function testInjectedActionParamsFromModule(): void
     {
-        $module = new \yii\base\Module('fake', new \yii\web\Application([
+        $module = new Module('fake', new Application([
             'id' => 'app',
             'basePath' => __DIR__,
             'components' => [
@@ -209,7 +213,7 @@ class ControllerTest extends TestCase
             ],
         ]));
         $module->set('yii\data\DataProviderInterface', [
-            'class' => \yii\data\ArrayDataProvider::className(),
+            'class' => ArrayDataProvider::className(),
         ]);
         // Use the PHP71 controller for this test
         $this->controller = new FakePhp71Controller('fake', $module);
@@ -217,17 +221,17 @@ class ControllerTest extends TestCase
 
         $injectionAction = new InlineAction('injection', $this->controller, 'actionModuleServiceInjection');
         $args = $this->controller->bindActionParams($injectionAction, []);
-        $this->assertInstanceOf(\yii\data\ArrayDataProvider::className(), $args[0]);
+        $this->assertInstanceOf(ArrayDataProvider::className(), $args[0]);
         $this->assertEquals('Module yii\base\Module DI: yii\data\DataProviderInterface $dataProvider', Yii::$app->requestedParams['dataProvider']);
     }
 
     /**
      * @see https://github.com/yiisoft/yii2/issues/17701
      */
-    public function testBindTypedActionParams()
+    public function testBindTypedActionParams(): void
     {
         // Use the PHP7 controller for this test
-        $this->controller = new FakePhp7Controller('fake', new \yii\web\Application([
+        $this->controller = new FakePhp7Controller('fake', new Application([
             'id' => 'app',
             'basePath' => __DIR__,
             'components' => [
@@ -278,7 +282,7 @@ class ControllerTest extends TestCase
         $this->controller->bindActionParams($aksi1, $params);
     }
 
-    public function testAsJson()
+    public function testAsJson(): void
     {
         $data = [
             'test' => 123,
@@ -291,7 +295,7 @@ class ControllerTest extends TestCase
         $this->assertEquals($data, $result->data);
     }
 
-    public function testAsXml()
+    public function testAsXml(): void
     {
         $data = [
             'test' => 123,
@@ -304,7 +308,7 @@ class ControllerTest extends TestCase
         $this->assertEquals($data, $result->data);
     }
 
-    public function testRedirect()
+    public function testRedirect(): void
     {
         $_SERVER['REQUEST_URI'] = 'http://test-domain.com/';
         $this->assertEquals($this->controller->redirect('')->headers->get('location'), '/');
@@ -321,7 +325,7 @@ class ControllerTest extends TestCase
         $this->assertEquals($this->controller->redirect(['//controller/index', 'slug' => 'äöüß!"§$%&/()'])->headers->get('location'), '/index.php?r=controller%2Findex&slug=%C3%A4%C3%B6%C3%BC%C3%9F%21%22%C2%A7%24%25%26%2F%28%29');
     }
 
-    public function testUnionBindingActionParams()
+    public function testUnionBindingActionParams(): void
     {
         if (PHP_VERSION_ID < 80000) {
             $this->markTestSkipped('Can not be tested on PHP < 8.0');
@@ -329,7 +333,7 @@ class ControllerTest extends TestCase
         }
 
         // Use the PHP80 controller for this test
-        $this->controller = new FakePhp80Controller('fake', new \yii\web\Application([
+        $this->controller = new FakePhp80Controller('fake', new Application([
             'id' => 'app',
             'basePath' => __DIR__,
             'components' => [
@@ -358,14 +362,14 @@ class ControllerTest extends TestCase
         $this->assertSame(1, $args[1]);
     }
 
-    public function testUnionBindingActionParamsWithArray()
+    public function testUnionBindingActionParamsWithArray(): void
     {
         if (PHP_VERSION_ID < 80000) {
             $this->markTestSkipped('Can not be tested on PHP < 8.0');
             return;
         }
         // Use the PHP80 controller for this test
-        $this->controller = new FakePhp80Controller('fake', new \yii\web\Application([
+        $this->controller = new FakePhp80Controller('fake', new Application([
             'id' => 'app',
             'basePath' => __DIR__,
             'components' => [
diff --git a/tests/framework/web/ErrorActionTest.php b/tests/framework/web/ErrorActionTest.php
index 17fd2b0057..c5b5538875 100644
--- a/tests/framework/web/ErrorActionTest.php
+++ b/tests/framework/web/ErrorActionTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\web;
 
+use InvalidArgumentException;
 use Yii;
 use yii\base\InvalidConfigException;
 use yii\base\UserException;
@@ -37,7 +38,7 @@ class ErrorActionTest extends TestCase
         return new TestController('test', Yii::$app, ['layout' => false, 'actionConfig' => $actionConfig]);
     }
 
-    public function testYiiException()
+    public function testYiiException(): void
     {
         Yii::$app->getErrorHandler()->exception = new InvalidConfigException('This message will not be shown to the user');
 
@@ -47,7 +48,7 @@ Message: An internal server error occurred.
 Exception: yii\base\InvalidConfigException', $this->getController()->runAction('error'));
     }
 
-    public function testUserException()
+    public function testUserException(): void
     {
         Yii::$app->getErrorHandler()->exception = new UserException('User can see this error message');
 
@@ -57,16 +58,16 @@ Message: User can see this error message
 Exception: yii\base\UserException', $this->getController()->runAction('error'));
     }
 
-    public function testAjaxRequest()
+    public function testAjaxRequest(): void
     {
         $_SERVER['HTTP_X_REQUESTED_WITH'] = 'XMLHttpRequest';
 
         $this->assertEquals('Not Found (#404): Page not found.', $this->getController()->runAction('error'));
     }
 
-    public function testGenericException()
+    public function testGenericException(): void
     {
-        Yii::$app->getErrorHandler()->exception = new \InvalidArgumentException('This message will not be shown to the user');
+        Yii::$app->getErrorHandler()->exception = new InvalidArgumentException('This message will not be shown to the user');
 
         $this->assertEquals('Name: Error
 Code: 500
@@ -74,9 +75,9 @@ Message: An internal server error occurred.
 Exception: InvalidArgumentException', $this->getController()->runAction('error'));
     }
 
-    public function testGenericExceptionCustomNameAndMessage()
+    public function testGenericExceptionCustomNameAndMessage(): void
     {
-        Yii::$app->getErrorHandler()->exception = new \InvalidArgumentException('This message will not be shown to the user');
+        Yii::$app->getErrorHandler()->exception = new InvalidArgumentException('This message will not be shown to the user');
 
         $controller = $this->getController([
             'defaultName' => 'Oops...',
@@ -89,7 +90,7 @@ Message: The system is drunk
 Exception: InvalidArgumentException', $controller->runAction('error'));
     }
 
-    public function testNoExceptionInHandler()
+    public function testNoExceptionInHandler(): void
     {
         $this->assertEquals('Name: Not Found (#404)
 Code: 404
@@ -97,7 +98,7 @@ Message: Page not found.
 Exception: yii\web\NotFoundHttpException', $this->getController()->runAction('error'));
     }
 
-    public function testDefaultView()
+    public function testDefaultView(): void
     {
         /** @var ErrorAction $action */
         $action = $this->getController()->createAction('error');
@@ -110,7 +111,7 @@ Exception: yii\web\NotFoundHttpException', $this->getController()->runAction('er
         $this->invokeMethod($action, 'renderHtmlResponse');
     }
 
-    public function testLayout()
+    public function testLayout(): void
     {
         $this->expectException('yii\base\ViewNotFoundException');
 
diff --git a/tests/framework/web/ErrorHandlerTest.php b/tests/framework/web/ErrorHandlerTest.php
index 6f94101053..638bf4b542 100644
--- a/tests/framework/web/ErrorHandlerTest.php
+++ b/tests/framework/web/ErrorHandlerTest.php
@@ -8,6 +8,9 @@
 
 namespace yiiunit\framework\web;
 
+use Exception;
+use yii\BaseYii;
+use yii\web\Application;
 use Yii;
 use yii\web\NotFoundHttpException;
 use yii\web\View;
@@ -30,7 +33,7 @@ class ErrorHandlerTest extends TestCase
         ]);
     }
 
-    public function testCorrectResponseCodeInErrorView()
+    public function testCorrectResponseCodeInErrorView(): void
     {
         /** @var ErrorHandler $handler */
         $handler = Yii::$app->getErrorHandler();
@@ -43,7 +46,7 @@ Message: This message is displayed to end user
 Exception: yii\web\NotFoundHttpException', $out);
     }
 
-    public function testFormatRaw()
+    public function testFormatRaw(): void
     {
         Yii::$app->response->format = yii\web\Response::FORMAT_RAW;
 
@@ -51,7 +54,7 @@ Exception: yii\web\NotFoundHttpException', $out);
         $handler = Yii::$app->getErrorHandler();
 
         ob_start(); // suppress response output
-        $this->invokeMethod($handler, 'renderException', [new \Exception('Test Exception')]);
+        $this->invokeMethod($handler, 'renderException', [new Exception('Test Exception')]);
         $out = ob_get_clean();
 
         $this->assertStringContainsString('Test Exception', $out);
@@ -63,7 +66,7 @@ Exception: yii\web\NotFoundHttpException', $out);
         );
     }
 
-    public function testFormatXml()
+    public function testFormatXml(): void
     {
         Yii::$app->response->format = yii\web\Response::FORMAT_XML;
 
@@ -71,7 +74,7 @@ Exception: yii\web\NotFoundHttpException', $out);
         $handler = Yii::$app->getErrorHandler();
 
         ob_start(); // suppress response output
-        $this->invokeMethod($handler, 'renderException', [new \Exception('Test Exception')]);
+        $this->invokeMethod($handler, 'renderException', [new Exception('Test Exception')]);
         $out = ob_get_clean();
 
         $this->assertStringContainsString('Test Exception', $out);
@@ -89,19 +92,19 @@ Exception: yii\web\NotFoundHttpException', $out);
         $this->assertArrayHasKey('line', $outArray);
     }
 
-    public function testClearAssetFilesInErrorView()
+    public function testClearAssetFilesInErrorView(): void
     {
         Yii::$app->getView()->registerJsFile('somefile.js');
         /** @var ErrorHandler $handler */
         $handler = Yii::$app->getErrorHandler();
         ob_start(); // suppress response output
-        $this->invokeMethod($handler, 'renderException', [new \Exception('Some Exception')]);
+        $this->invokeMethod($handler, 'renderException', [new Exception('Some Exception')]);
         ob_get_clean();
         $out = Yii::$app->response->data;
         $this->assertEquals("Exception View\n", $out);
     }
 
-    public function testClearAssetFilesInErrorActionView()
+    public function testClearAssetFilesInErrorActionView(): void
     {
         Yii::$app->getErrorHandler()->errorAction = 'test/error';
         Yii::$app->getView()->registerJs("alert('hide me')", View::POS_END);
@@ -115,13 +118,13 @@ Exception: yii\web\NotFoundHttpException', $out);
         $this->assertStringNotContainsString('<script', $out);
     }
 
-    public function testRenderCallStackItem()
+    public function testRenderCallStackItem(): void
     {
         $handler = Yii::$app->getErrorHandler();
         $handler->traceLine = '<a href="netbeans://open?file={file}&line={line}">{html}</a>';
-        $file = \yii\BaseYii::getAlias('@yii/web/Application.php');
+        $file = BaseYii::getAlias('@yii/web/Application.php');
 
-        $out = $handler->renderCallStackItem($file, 63, \yii\web\Application::className(), null, null, null);
+        $out = $handler->renderCallStackItem($file, 63, Application::className(), null, null, null);
 
         $this->assertStringContainsString('<a href="netbeans://open?file=' . $file . '&line=63">', $out);
     }
@@ -159,14 +162,14 @@ Exception: yii\web\NotFoundHttpException', $out);
     /**
      * @dataProvider dataHtmlEncode
      */
-    public function testHtmlEncode($text, $expected)
+    public function testHtmlEncode($text, $expected): void
     {
         $handler = Yii::$app->getErrorHandler();
 
         $this->assertSame($expected, $handler->htmlEncode($text));
     }
 
-    public function testHtmlEncodeWithUnicodeSequence()
+    public function testHtmlEncodeWithUnicodeSequence(): void
     {
         $handler = Yii::$app->getErrorHandler();
 
diff --git a/tests/framework/web/FormatterTest.php b/tests/framework/web/FormatterTest.php
index cc6d03cf2d..811de609b5 100644
--- a/tests/framework/web/FormatterTest.php
+++ b/tests/framework/web/FormatterTest.php
@@ -8,10 +8,11 @@
 
 namespace yiiunit\framework\web;
 
+use yiiunit\TestCase;
 use yii\web\Response;
 use yii\web\ResponseFormatterInterface;
 
-abstract class FormatterTest extends \yiiunit\TestCase
+abstract class FormatterTest extends TestCase
 {
     /**
      * @var Response
@@ -37,7 +38,7 @@ abstract class FormatterTest extends \yiiunit\TestCase
     /**
      * Formatter should not format null.
      */
-    public function testFormatNull()
+    public function testFormatNull(): void
     {
         $this->response->data = null;
         $this->formatter->format($this->response);
@@ -49,7 +50,7 @@ abstract class FormatterTest extends \yiiunit\TestCase
      * @param string $json the expected JSON body
      * @dataProvider formatScalarDataProvider
      */
-    public function testFormatScalar($data, $json)
+    public function testFormatScalar($data, $json): void
     {
         $this->response->data = $data;
         $this->formatter->format($this->response);
@@ -61,7 +62,7 @@ abstract class FormatterTest extends \yiiunit\TestCase
      * @param string $json the expected JSON body
      * @dataProvider formatArrayDataProvider
      */
-    public function testFormatArrays($data, $json)
+    public function testFormatArrays($data, $json): void
     {
         $this->response->data = $data;
         $this->formatter->format($this->response);
@@ -73,7 +74,7 @@ abstract class FormatterTest extends \yiiunit\TestCase
      * @param string $json the expected JSON body
      * @dataProvider formatTraversableObjectDataProvider
      */
-    public function testFormatTraversableObjects($data, $json)
+    public function testFormatTraversableObjects($data, $json): void
     {
         $this->response->data = $data;
         $this->formatter->format($this->response);
@@ -85,7 +86,7 @@ abstract class FormatterTest extends \yiiunit\TestCase
      * @param string $json the expected JSON body
      * @dataProvider formatObjectDataProvider
      */
-    public function testFormatObjects($data, $json)
+    public function testFormatObjects($data, $json): void
     {
         $this->response->data = $data;
         $this->formatter->format($this->response);
@@ -97,7 +98,7 @@ abstract class FormatterTest extends \yiiunit\TestCase
      * @param string $expectedResult the expected body
      * @dataProvider formatModelDataProvider
      */
-    public function testFormatModels($data, $expectedResult)
+    public function testFormatModels($data, $expectedResult): void
     {
         $this->response->data = $data;
         $this->formatter->format($this->response);
diff --git a/tests/framework/web/GroupUrlRuleTest.php b/tests/framework/web/GroupUrlRuleTest.php
index 2902e18b8d..a870a3bce1 100644
--- a/tests/framework/web/GroupUrlRuleTest.php
+++ b/tests/framework/web/GroupUrlRuleTest.php
@@ -25,7 +25,7 @@ class GroupUrlRuleTest extends TestCase
         $this->mockApplication();
     }
 
-    public function testCreateUrl()
+    public function testCreateUrl(): void
     {
         $manager = new UrlManager(['cache' => null]);
         $suites = $this->getTestsForCreateUrl();
@@ -41,7 +41,7 @@ class GroupUrlRuleTest extends TestCase
         }
     }
 
-    public function testParseRequest()
+    public function testParseRequest(): void
     {
         $manager = new UrlManager(['cache' => null]);
         $request = new Request(['hostInfo' => 'http://en.example.com']);
@@ -63,7 +63,7 @@ class GroupUrlRuleTest extends TestCase
         }
     }
 
-    public function testParseVerb()
+    public function testParseVerb(): void
     {
         $config = [
             'prefix' => 'admin',
diff --git a/tests/framework/web/HeaderCollectionTest.php b/tests/framework/web/HeaderCollectionTest.php
index 0c0b4cd558..59eb2254c7 100644
--- a/tests/framework/web/HeaderCollectionTest.php
+++ b/tests/framework/web/HeaderCollectionTest.php
@@ -16,7 +16,7 @@ use yiiunit\TestCase;
  */
 class HeaderCollectionTest extends TestCase
 {
-    public function testFromArray()
+    public function testFromArray(): void
     {
         $headerCollection = new HeaderCollection();
         $location = 'my-test-location';
@@ -26,7 +26,7 @@ class HeaderCollectionTest extends TestCase
         $this->assertEquals($location, $headerCollection->get('Location'));
     }
 
-    public function testSetter()
+    public function testSetter(): void
     {
         $headerCollection = new HeaderCollection();
 
@@ -57,7 +57,7 @@ class HeaderCollectionTest extends TestCase
         $this->assertSame('3', $headerCollection->get('X-Header'));
     }
 
-    public function testSetterDefault()
+    public function testSetterDefault(): void
     {
         $headerCollection = new HeaderCollection();
         $headerCollection->setDefault('X-Header', '1');
@@ -67,7 +67,7 @@ class HeaderCollectionTest extends TestCase
         $this->assertSame(['1'], $headerCollection->get('X-Header', null, false));
     }
 
-    public function testAdder()
+    public function testAdder(): void
     {
         $headerCollection = new HeaderCollection();
         $headerCollection->add('X-Header', '1');
@@ -89,7 +89,7 @@ class HeaderCollectionTest extends TestCase
         $this->assertSame(['X-Header' => ['1', '2']], $headerCollection->toOriginalArray());
     }
 
-    public function testRemover()
+    public function testRemover(): void
     {
         $headerCollection = new HeaderCollection();
         $headerCollection->add('X-Header', '1');
diff --git a/tests/framework/web/JsonResponseFormatterTest.php b/tests/framework/web/JsonResponseFormatterTest.php
index c5ba32f141..6f6229729f 100644
--- a/tests/framework/web/JsonResponseFormatterTest.php
+++ b/tests/framework/web/JsonResponseFormatterTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\web;
 
+use SplStack;
 use yii\helpers\Json;
 use yii\web\JsonResponseFormatter;
 use yiiunit\framework\web\stubs\ModelStub;
@@ -92,7 +93,7 @@ class JsonResponseFormatterTest extends FormatterTest
 
     public function formatTraversableObjectDataProvider()
     {
-        $postsStack = new \SplStack();
+        $postsStack = new SplStack();
         $postsStack->push(new Post(915, 'record1'));
         $postsStack->push(new Post(456, 'record2'));
 
@@ -165,7 +166,7 @@ class JsonResponseFormatterTest extends FormatterTest
      * @param string $prettyJson the expected pretty JSON body
      * @dataProvider formatArrayDataProvider
      */
-    public function testFormatArraysPretty($data, $json, $prettyJson)
+    public function testFormatArraysPretty($data, $json, $prettyJson): void
     {
         $this->response->data = $data;
         $this->formatter->prettyPrint = true;
@@ -178,7 +179,7 @@ class JsonResponseFormatterTest extends FormatterTest
      * @param string $contentTypeExpected Expected value of the response `Content-Type` header.
      * @dataProvider contentTypeGenerationDataProvider
      */
-    public function testContentTypeGeneration($configuration, $contentTypeExpected)
+    public function testContentTypeGeneration($configuration, $contentTypeExpected): void
     {
         $formatter = $this->getFormatterInstance($configuration);
         $formatter->format($this->response);
@@ -190,7 +191,7 @@ class JsonResponseFormatterTest extends FormatterTest
     /**
      * Formatter must return 'null' string.
      */
-    public function testFormatNull()
+    public function testFormatNull(): void
     {
         $this->response->data = null;
         $this->formatter->format($this->response);
@@ -201,7 +202,7 @@ class JsonResponseFormatterTest extends FormatterTest
      * Formatter must return early sets content,
      * e.g. content may be sets by PageCache filter
      */
-    public function testFormatFilledContent()
+    public function testFormatFilledContent(): void
     {
         $content = '{"text": "early seted content"}';
         $this->response->data = null;
@@ -213,7 +214,7 @@ class JsonResponseFormatterTest extends FormatterTest
     /**
      * Formatter configuration keepObjectType affects how zero-indexed objects are encoded
      */
-    public function testFormatZeroIndexedObjectKeepObject()
+    public function testFormatZeroIndexedObjectKeepObject(): void
     {
         $formatter = $this->getFormatterInstance([
             'keepObjectType' => true,
@@ -226,7 +227,7 @@ class JsonResponseFormatterTest extends FormatterTest
     /**
      * Formatter configuration keepObjectType affects how zero-indexed objects are encoded
      */
-    public function testFormatZeroIndexedObjectAllowArray()
+    public function testFormatZeroIndexedObjectAllowArray(): void
     {
         $formatter = $this->getFormatterInstance([
             'keepObjectType' => false,
@@ -239,7 +240,7 @@ class JsonResponseFormatterTest extends FormatterTest
     /**
      * Formatter configuration keepObjectType reverts Json::$keepObjectType to its previous value
      */
-    public function testFormatCleanupKeepObjectType()
+    public function testFormatCleanupKeepObjectType(): void
     {
         $default = Json::$keepObjectType;
         Json::$keepObjectType = false;
diff --git a/tests/framework/web/LinkTest.php b/tests/framework/web/LinkTest.php
index 3251b25605..44a33554b0 100644
--- a/tests/framework/web/LinkTest.php
+++ b/tests/framework/web/LinkTest.php
@@ -16,7 +16,7 @@ use yiiunit\TestCase;
  */
 class LinkTest extends TestCase
 {
-    public function testSerializeLinkInSimpleArrayWillRemoveNotSetValues()
+    public function testSerializeLinkInSimpleArrayWillRemoveNotSetValues(): void
     {
         $managerLink = new Link([
             'href' => 'https://example.com/users/4',
@@ -41,7 +41,7 @@ class LinkTest extends TestCase
         ]));
     }
 
-    public function testSerializeNestedArrayWithLinkWillSerialize()
+    public function testSerializeNestedArrayWithLinkWillSerialize(): void
     {
         $linkData = [
             'self' => new Link([
diff --git a/tests/framework/web/MultipartFormDataParserTest.php b/tests/framework/web/MultipartFormDataParserTest.php
index 50e23646e8..fb7914a934 100644
--- a/tests/framework/web/MultipartFormDataParserTest.php
+++ b/tests/framework/web/MultipartFormDataParserTest.php
@@ -13,7 +13,7 @@ use yiiunit\TestCase;
 
 class MultipartFormDataParserTest extends TestCase
 {
-    public function testParse()
+    public function testParse(): void
     {
         if (defined('HHVM_VERSION')) {
             static::markTestSkipped('Can not test on HHVM because it does not support proper handling of the temporary files.');
@@ -53,7 +53,7 @@ class MultipartFormDataParserTest extends TestCase
         $this->assertStringEqualsFile($_FILES['Item']['tmp_name']['file'], 'item file content');
     }
 
-    public function testParseWithDoubleQuotes()
+    public function testParseWithDoubleQuotes(): void
     {
         if (defined('HHVM_VERSION')) {
             static::markTestSkipped('Can not test on HHVM because it does not support proper handling of the temporary files.');
@@ -96,7 +96,7 @@ class MultipartFormDataParserTest extends TestCase
     /**
      * @depends testParse
      */
-    public function testNotEmptyPost()
+    public function testNotEmptyPost(): void
     {
         $parser = new MultipartFormDataParser();
 
@@ -112,7 +112,7 @@ class MultipartFormDataParserTest extends TestCase
     /**
      * @depends testParse
      */
-    public function testNotEmptyFiles()
+    public function testNotEmptyFiles(): void
     {
         $parser = new MultipartFormDataParser();
 
@@ -134,7 +134,7 @@ class MultipartFormDataParserTest extends TestCase
     /**
      * @depends testParse
      */
-    public function testUploadFileMaxCount()
+    public function testUploadFileMaxCount(): void
     {
         $parser = new MultipartFormDataParser();
         $parser->setUploadFileMaxCount(2);
@@ -153,7 +153,7 @@ class MultipartFormDataParserTest extends TestCase
     /**
      * @depends testParse
      */
-    public function testUploadFileMaxSize()
+    public function testUploadFileMaxSize(): void
     {
         $parser = new MultipartFormDataParser();
         $parser->setUploadFileMaxSize(20);
@@ -170,7 +170,7 @@ class MultipartFormDataParserTest extends TestCase
         $this->assertEquals(UPLOAD_ERR_INI_SIZE, $_FILES['thirdFile']['error']);
     }
 
-    public function testUploadFileAsArray()
+    public function testUploadFileAsArray(): void
     {
         $parser = new MultipartFormDataParser();
 
@@ -192,7 +192,7 @@ class MultipartFormDataParserTest extends TestCase
      * @depends testNotEmptyPost
      * @depends testNotEmptyFiles
      */
-    public function testForce()
+    public function testForce(): void
     {
         $parser = new MultipartFormDataParser();
         $parser->force = true;
@@ -223,7 +223,7 @@ class MultipartFormDataParserTest extends TestCase
         $this->assertFalse(isset($_FILES['existingFile']));
     }
 
-    public function testParseUnicodeInFileName()
+    public function testParseUnicodeInFileName(): void
     {
         $unicodeName = 'х.jpg'; // this is Russian "х"
 
diff --git a/tests/framework/web/RequestTest.php b/tests/framework/web/RequestTest.php
index e4361628f1..851443cb17 100644
--- a/tests/framework/web/RequestTest.php
+++ b/tests/framework/web/RequestTest.php
@@ -8,6 +8,9 @@
 
 namespace yiiunit\framework\web;
 
+use Yii;
+use yii\base\InvalidConfigException;
+use stdClass;
 use yii\web\Request;
 use yiiunit\TestCase;
 
@@ -17,7 +20,7 @@ use yiiunit\TestCase;
  */
 class RequestTest extends TestCase
 {
-    public function testParseAcceptHeader()
+    public function testParseAcceptHeader(): void
     {
         $request = new Request();
 
@@ -40,7 +43,7 @@ class RequestTest extends TestCase
             text/x-dvi; q=0.8, text/x-c'));
     }
 
-    public function testPreferredLanguage()
+    public function testPreferredLanguage(): void
     {
         $this->mockApplication([
             'language' => 'en',
@@ -84,7 +87,7 @@ class RequestTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/14542
      */
-    public function testCsrfTokenContainsASCIIOnly()
+    public function testCsrfTokenContainsASCIIOnly(): void
     {
         $this->mockWebApplication();
 
@@ -95,7 +98,7 @@ class RequestTest extends TestCase
         $this->assertMatchesRegularExpression('~[-_=a-z0-9]~i', $token);
     }
 
-    public function testCsrfTokenValidation()
+    public function testCsrfTokenValidation(): void
     {
         $this->mockWebApplication();
 
@@ -139,7 +142,7 @@ class RequestTest extends TestCase
         }
     }
 
-    public function testIssue15317()
+    public function testIssue15317(): void
     {
         $this->mockWebApplication();
         $_COOKIE[(new Request())->csrfParam] = '';
@@ -148,7 +151,7 @@ class RequestTest extends TestCase
         $request->enableCookieValidation = false;
 
         $_SERVER['REQUEST_METHOD'] = 'POST';
-        \Yii::$app->security->unmaskToken('');
+        Yii::$app->security->unmaskToken('');
         $this->assertFalse($request->validateCsrfToken(''));
 
         // When an empty CSRF token is given it is regenerated.
@@ -158,7 +161,7 @@ class RequestTest extends TestCase
     /**
      * Test CSRF token validation by POST param.
      */
-    public function testCsrfTokenPost()
+    public function testCsrfTokenPost(): void
     {
         $this->mockWebApplication();
 
@@ -186,7 +189,7 @@ class RequestTest extends TestCase
     /**
      * Test CSRF token validation by POST param.
      */
-    public function testCsrfTokenHeader()
+    public function testCsrfTokenHeader(): void
     {
         $this->mockWebApplication();
 
@@ -212,7 +215,7 @@ class RequestTest extends TestCase
         }
     }
 
-    public function testCustomSafeMethodsCsrfTokenValidation()
+    public function testCustomSafeMethodsCsrfTokenValidation(): void
     {
         $this->mockWebApplication();
 
@@ -248,7 +251,7 @@ class RequestTest extends TestCase
         }
     }
 
-    public function testCsrfHeaderValidation()
+    public function testCsrfHeaderValidation(): void
     {
         $this->mockWebApplication();
 
@@ -273,7 +276,7 @@ class RequestTest extends TestCase
         }
     }
 
-    public function testCustomHeaderCsrfHeaderValidation()
+    public function testCustomHeaderCsrfHeaderValidation(): void
     {
         $this->mockWebApplication();
 
@@ -293,7 +296,7 @@ class RequestTest extends TestCase
         }
     }
 
-    public function testCustomUnsafeMethodsCsrfHeaderValidation()
+    public function testCustomUnsafeMethodsCsrfHeaderValidation(): void
     {
         $this->mockWebApplication();
 
@@ -320,7 +323,7 @@ class RequestTest extends TestCase
         }
     }
 
-    public function testNoCsrfTokenCsrfHeaderValidation()
+    public function testNoCsrfTokenCsrfHeaderValidation(): void
     {
         $this->mockWebApplication();
 
@@ -330,7 +333,7 @@ class RequestTest extends TestCase
         $this->assertEquals($request->getCsrfToken(), null);
     }
 
-    public function testResolve()
+    public function testResolve(): void
     {
         $this->mockWebApplication([
             'components' => [
@@ -497,7 +500,7 @@ class RequestTest extends TestCase
      * @param array $server
      * @param array $expected
      */
-    public function testGetHostInfo($server, $expected)
+    public function testGetHostInfo($server, $expected): void
     {
         $original = $_SERVER;
         $_SERVER = $server;
@@ -535,7 +538,7 @@ class RequestTest extends TestCase
         $_SERVER = $original;
     }
 
-    public function testSetHostInfo()
+    public function testSetHostInfo(): void
     {
         $request = new Request();
 
@@ -548,27 +551,27 @@ class RequestTest extends TestCase
         $this->assertSame('servername.com', $request->getHostName());
     }
 
-    public function testGetScriptFileWithEmptyServer()
+    public function testGetScriptFileWithEmptyServer(): void
     {
         $request = new Request();
         $_SERVER = [];
 
-        $this->expectException(\yii\base\InvalidConfigException::class);
+        $this->expectException(InvalidConfigException::class);
 
         $request->getScriptFile();
     }
 
-    public function testGetScriptUrlWithEmptyServer()
+    public function testGetScriptUrlWithEmptyServer(): void
     {
         $request = new Request();
         $_SERVER = [];
 
-        $this->expectException(\yii\base\InvalidConfigException::class);
+        $this->expectException(InvalidConfigException::class);
 
         $request->getScriptUrl();
     }
 
-    public function testGetServerName()
+    public function testGetServerName(): void
     {
         $request = new Request();
 
@@ -579,7 +582,7 @@ class RequestTest extends TestCase
         $this->assertNull($request->getServerName());
     }
 
-    public function testGetServerPort()
+    public function testGetServerPort(): void
     {
         $request = new Request();
 
@@ -680,7 +683,7 @@ class RequestTest extends TestCase
      * @param array $server
      * @param bool $expected
      */
-    public function testGetIsSecureConnection($server, $expected)
+    public function testGetIsSecureConnection($server, $expected): void
     {
         $original = $_SERVER;
         $_SERVER = $server;
@@ -734,7 +737,7 @@ class RequestTest extends TestCase
      * @param array $server
      * @param bool $expected
      */
-    public function testGetIsSecureConnectionWithoutTrustedHost($server, $expected)
+    public function testGetIsSecureConnectionWithoutTrustedHost($server, $expected): void
     {
         $original = $_SERVER;
         $_SERVER = $server;
@@ -898,7 +901,7 @@ class RequestTest extends TestCase
      * @param array $server
      * @param string $expected
      */
-    public function testGetUserIP($server, $expected)
+    public function testGetUserIP($server, $expected): void
     {
         $original = $_SERVER;
         $_SERVER = $server;
@@ -954,7 +957,7 @@ class RequestTest extends TestCase
     * @param array $server
     * @param string $expected
     */
-    public function testGetUserIPWithoutTrustedHost($server, $expected)
+    public function testGetUserIPWithoutTrustedHost($server, $expected): void
     {
         $original = $_SERVER;
         $_SERVER = $server;
@@ -1001,7 +1004,7 @@ class RequestTest extends TestCase
      * @param array $server
      * @param string $expected
      */
-    public function testGetMethod($server, $expected)
+    public function testGetMethod($server, $expected): void
     {
         $original = $_SERVER;
         $_SERVER = $server;
@@ -1033,7 +1036,7 @@ class RequestTest extends TestCase
      * @param array $server
      * @param bool $expected
      */
-    public function testGetIsAjax($server, $expected)
+    public function testGetIsAjax($server, $expected): void
     {
         $original = $_SERVER;
         $_SERVER = $server;
@@ -1066,7 +1069,7 @@ class RequestTest extends TestCase
      * @param array $server
      * @param bool $expected
      */
-    public function testGetIsPjax($server, $expected)
+    public function testGetIsPjax($server, $expected): void
     {
         $original = $_SERVER;
         $_SERVER = $server;
@@ -1076,7 +1079,7 @@ class RequestTest extends TestCase
         $_SERVER = $original;
     }
 
-    public function testGetOrigin()
+    public function testGetOrigin(): void
     {
         $_SERVER['HTTP_ORIGIN'] = 'https://www.w3.org';
         $request = new Request();
@@ -1106,7 +1109,7 @@ class RequestTest extends TestCase
      * @param string $secret
      * @param array $expected
      */
-    public function testHttpAuthCredentialsFromHttpAuthorizationHeader($secret, $expected)
+    public function testHttpAuthCredentialsFromHttpAuthorizationHeader($secret, $expected): void
     {
         $original = $_SERVER;
 
@@ -1125,7 +1128,7 @@ class RequestTest extends TestCase
         $_SERVER = $original;
     }
 
-    public function testHttpAuthCredentialsFromServerSuperglobal()
+    public function testHttpAuthCredentialsFromServerSuperglobal(): void
     {
         $original = $_SERVER;
         list($user, $pw) = ['foo', 'bar'];
@@ -1142,7 +1145,7 @@ class RequestTest extends TestCase
         $_SERVER = $original;
     }
 
-    public function testGetBodyParam()
+    public function testGetBodyParam(): void
     {
         $request = new Request();
 
@@ -1156,7 +1159,7 @@ class RequestTest extends TestCase
         $this->assertSame('default', $request->getBodyParam('unexisting', 'default'));
 
         // @see https://github.com/yiisoft/yii2/issues/14135
-        $bodyParams = new \stdClass();
+        $bodyParams = new stdClass();
         $bodyParams->someParam = 'some value';
         $bodyParams->{'param.dot'} = 'value.dot';
         $request->setBodyParams($bodyParams);
@@ -1178,7 +1181,7 @@ class RequestTest extends TestCase
     /**
      * @dataProvider getBodyParamsDataProvider
      */
-    public function testGetBodyParams($contentType, $rawBody, array $expected)
+    public function testGetBodyParams($contentType, $rawBody, array $expected): void
     {
         $_SERVER['CONTENT_TYPE'] = $contentType;
         $request = new Request();
@@ -1213,7 +1216,7 @@ class RequestTest extends TestCase
     /**
      * @dataProvider trustedHostAndInjectedXForwardedForDataProvider
      */
-    public function testTrustedHostAndInjectedXForwardedFor($remoteAddress, $xForwardedFor, $ipHeaders, $trustedHosts, $expectedUserIp)
+    public function testTrustedHostAndInjectedXForwardedFor($remoteAddress, $xForwardedFor, $ipHeaders, $trustedHosts, $expectedUserIp): void
     {
         $_SERVER['REMOTE_ADDR'] = $remoteAddress;
         $_SERVER['HTTP_X_FORWARDED_FOR'] = $xForwardedFor;
@@ -1242,7 +1245,7 @@ class RequestTest extends TestCase
     /**
      * @dataProvider trustedHostAndXForwardedPortDataProvider
      */
-    public function testTrustedHostAndXForwardedPort($remoteAddress, $requestPort, $xForwardedPort, $trustedHosts, $expectedPort)
+    public function testTrustedHostAndXForwardedPort($remoteAddress, $requestPort, $xForwardedPort, $trustedHosts, $expectedPort): void
     {
         $_SERVER['REMOTE_ADDR'] = $remoteAddress;
         $_SERVER['SERVER_PORT'] = $requestPort;
@@ -1261,7 +1264,7 @@ class RequestTest extends TestCase
      *              ["POST", "DELETE", "DELETE"]
      *              ["POST", "CUSTOM", "CUSTOM"]
      */
-    public function testRequestMethodCanNotBeDowngraded($requestMethod, $requestOverrideMethod, $expectedMethod)
+    public function testRequestMethodCanNotBeDowngraded($requestMethod, $requestOverrideMethod, $expectedMethod): void
     {
         $request = new Request();
 
@@ -1300,7 +1303,7 @@ class RequestTest extends TestCase
     /**
      * @dataProvider alreadyResolvedIpDataProvider
      */
-    public function testAlreadyResolvedIp($remoteAddress, $xForwardedFor, $xForwardedProto, $trustedHosts, $expectedRemoteAddress, $expectedUserIp, $expectedIsSecureConnection)
+    public function testAlreadyResolvedIp($remoteAddress, $xForwardedFor, $xForwardedProto, $trustedHosts, $expectedRemoteAddress, $expectedUserIp, $expectedIsSecureConnection): void
     {
         $_SERVER['REMOTE_ADDR'] = $remoteAddress;
         $_SERVER['HTTP_X_FORWARDED_FOR'] = $xForwardedFor;
@@ -1365,7 +1368,7 @@ class RequestTest extends TestCase
     /**
      * @dataProvider parseForwardedHeaderDataProvider
      */
-    public function testParseForwardedHeaderParts($remoteAddress, $forwardedHeader, $expectedHostInfo, $expectedUserIp)
+    public function testParseForwardedHeaderParts($remoteAddress, $forwardedHeader, $expectedHostInfo, $expectedUserIp): void
     {
         $_SERVER['REMOTE_ADDR'] = $remoteAddress;
         $_SERVER['HTTP_HOST'] = 'example.com';
@@ -1388,7 +1391,7 @@ class RequestTest extends TestCase
         $this->assertSame($expectedHostInfo, $request->hostInfo, 'Host info fail!');
     }
 
-    public function testForwardedNotTrusted()
+    public function testForwardedNotTrusted(): void
     {
         $_SERVER['REMOTE_ADDR'] = '192.168.10.10';
         $_SERVER['HTTP_HOST'] = 'example.com';
diff --git a/tests/framework/web/ResponseTest.php b/tests/framework/web/ResponseTest.php
index ce164d741f..f139ab5f08 100644
--- a/tests/framework/web/ResponseTest.php
+++ b/tests/framework/web/ResponseTest.php
@@ -8,6 +8,9 @@
 
 namespace yiiunit\framework\web;
 
+use yiiunit\TestCase;
+use DateTime;
+use DateTimeImmutable;
 use Error;
 use Exception;
 use RuntimeException;
@@ -21,10 +24,10 @@ use yiiunit\framework\web\mocks\TestRequestComponent;
 /**
  * @group web
  */
-class ResponseTest extends \yiiunit\TestCase
+class ResponseTest extends TestCase
 {
     /**
-     * @var \yii\web\Response
+     * @var Response
      */
     public $response;
 
@@ -38,7 +41,7 @@ class ResponseTest extends \yiiunit\TestCase
                 ],
             ],
         ]);
-        $this->response = new \yii\web\Response();
+        $this->response = new Response();
     }
 
     public function rightRanges()
@@ -59,7 +62,7 @@ class ResponseTest extends \yiiunit\TestCase
      * @param int $length
      * @param string $expectedContent
      */
-    public function testSendFileRanges($rangeHeader, $expectedHeader, $length, $expectedContent)
+    public function testSendFileRanges($rangeHeader, $expectedHeader, $length, $expectedContent): void
     {
         $dataFile = Yii::getAlias('@yiiunit/data/web/data.txt');
         $fullContent = file_get_contents($dataFile);
@@ -96,7 +99,7 @@ class ResponseTest extends \yiiunit\TestCase
      * @dataProvider wrongRanges
      * @param string $rangeHeader
      */
-    public function testSendFileWrongRanges($rangeHeader)
+    public function testSendFileWrongRanges($rangeHeader): void
     {
         $this->expectException('yii\web\RangeNotSatisfiableHttpException');
 
@@ -113,7 +116,7 @@ class ResponseTest extends \yiiunit\TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/7529
      */
-    public function testSendContentAsFile()
+    public function testSendContentAsFile(): void
     {
         ob_start();
         $this->response->sendContentAsFile('test', 'test.txt')->send();
@@ -127,7 +130,7 @@ class ResponseTest extends \yiiunit\TestCase
         static::assertEquals(4, $headers->get('Content-Length'));
     }
 
-    public function testRedirect()
+    public function testRedirect(): void
     {
         $_SERVER['REQUEST_URI'] = 'http://test-domain.com/';
         $this->assertEquals('/', $this->response->redirect('')->headers->get('location'));
@@ -175,7 +178,7 @@ class ResponseTest extends \yiiunit\TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/19795
      */
-    public function testRedirectNewLine()
+    public function testRedirectNewLine(): void
     {
         $this->expectException('yii\base\InvalidRouteException');
 
@@ -185,7 +188,7 @@ class ResponseTest extends \yiiunit\TestCase
     /**
      * @dataProvider dataProviderAjaxRedirectInternetExplorer11
      */
-    public function testAjaxRedirectInternetExplorer11($userAgent, $statusCodes)
+    public function testAjaxRedirectInternetExplorer11($userAgent, $statusCodes): void
     {
         $_SERVER['REQUEST_URI'] = 'http://test-domain.com/';
         $request = Yii::$app->request;
@@ -239,7 +242,7 @@ class ResponseTest extends \yiiunit\TestCase
      * @param Exception $exception
      * @param int $statusCode
      */
-    public function testSetStatusCodeByException($exception, $statusCode)
+    public function testSetStatusCodeByException($exception, $statusCode): void
     {
         $this->response->setStatusCodeByException($exception);
         $this->assertEquals($statusCode, $this->response->getStatusCode());
@@ -248,7 +251,7 @@ class ResponseTest extends \yiiunit\TestCase
     /**
      * @see https://github.com/yiisoft/yii2/pull/18290
      */
-    public function testNonSeekableStream()
+    public function testNonSeekableStream(): void
     {
         $stream = fopen('php://output', 'r+');
         ob_start();
@@ -313,7 +316,7 @@ class ResponseTest extends \yiiunit\TestCase
     /**
      * @dataProvider formatDataProvider
      */
-    public function testSkipFormatter($format, $content)
+    public function testSkipFormatter($format, $content): void
     {
         $response = new Response();
         $response->format = $format;
@@ -328,19 +331,19 @@ class ResponseTest extends \yiiunit\TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/17094
      */
-    public function testEmptyContentOn204()
+    public function testEmptyContentOn204(): void
     {
         $this->assertEmptyContentOn(204);
     }
 
-    public function testSettingContentToNullOn204()
+    public function testSettingContentToNullOn204(): void
     {
         $this->assertEmptyContentOn(204, function (Response $response) {
             $this->assertSame($response->content, '');
         });
     }
 
-    public function testSettingStreamToNullOn204()
+    public function testSettingStreamToNullOn204(): void
     {
         $this->assertSettingStreamToNullOn(204);
     }
@@ -348,7 +351,7 @@ class ResponseTest extends \yiiunit\TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/18199
      */
-    public function testEmptyContentOn304()
+    public function testEmptyContentOn304(): void
     {
         $this->assertEmptyContentOn(304);
     }
@@ -356,19 +359,19 @@ class ResponseTest extends \yiiunit\TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/18199
      */
-    public function testSettingContentToNullOn304()
+    public function testSettingContentToNullOn304(): void
     {
         $this->assertEmptyContentOn(304, function (Response $response) {
             $this->assertSame($response->content, '');
         });
     }
 
-    public function testSettingStreamToNullOn304()
+    public function testSettingStreamToNullOn304(): void
     {
         $this->assertSettingStreamToNullOn(304);
     }
 
-    public function testSendFileWithInvalidCharactersInFileName()
+    public function testSendFileWithInvalidCharactersInFileName(): void
     {
         $response = new Response();
         $dataFile = Yii::getAlias('@yiiunit/data/web/data.txt');
@@ -384,7 +387,7 @@ class ResponseTest extends \yiiunit\TestCase
     /**
      * @dataProvider cookiesTestProvider
      */
-    public function testCookies($cookieConfig, $expected)
+    public function testCookies($cookieConfig, $expected): void
     {
         $response = new Response();
         $response->cookies->add(new Cookie(array_merge(
@@ -435,11 +438,11 @@ class ResponseTest extends \yiiunit\TestCase
         if (version_compare(PHP_VERSION, '5.5.0', '>=')) {
             $testCases = array_merge($testCases, [
                 'expire-as-date_time' => [
-                    ['expire' => new \DateTime('@' . $expireInt)],
+                    ['expire' => new DateTime('@' . $expireInt)],
                     ['expires' => $expireString],
                 ],
                 'expire-as-date_time_immutable' => [
-                    ['expire' => new \DateTimeImmutable('@' . $expireInt)],
+                    ['expire' => new DateTimeImmutable('@' . $expireInt)],
                     ['expires' => $expireString],
                 ],
             ]);
@@ -485,7 +488,7 @@ class ResponseTest extends \yiiunit\TestCase
                 }
             }
             if ($name === null) {
-                throw new \Exception('Could not determine cookie name for header "' . $header . '".');
+                throw new Exception('Could not determine cookie name for header "' . $header . '".');
             }
             $cookies[$name] = $params;
         }
diff --git a/tests/framework/web/UploadedFileTest.php b/tests/framework/web/UploadedFileTest.php
index ead42ad555..7d01612846 100644
--- a/tests/framework/web/UploadedFileTest.php
+++ b/tests/framework/web/UploadedFileTest.php
@@ -47,7 +47,7 @@ class UploadedFileTest extends TestCase
         ];
     }
 
-    private function generateFakeFiles()
+    private function generateFakeFiles(): void
     {
         $_FILES['ModelStub[prod_image]'] = $this->generateFakeFileData();
         $_FILES['ModelStub[prod_images][]'] = $this->generateFakeFileData();
@@ -64,7 +64,7 @@ class UploadedFileTest extends TestCase
 
     // Tests :
 
-    public function testGetInstance()
+    public function testGetInstance(): void
     {
         $productImage = UploadedFile::getInstance(new ModelStub(), 'prod_image');
         $vendorImage = VendorImage::getInstance(new ModelStub(), 'vendor_image');
@@ -73,7 +73,7 @@ class UploadedFileTest extends TestCase
         $this->assertInstanceOf(VendorImage::className(), $vendorImage);
     }
 
-    public function testGetInstances()
+    public function testGetInstances(): void
     {
         $productImages = UploadedFile::getInstances(new ModelStub(), 'prod_images');
         $vendorImages = VendorImage::getInstances(new ModelStub(), 'vendor_images');
@@ -87,7 +87,7 @@ class UploadedFileTest extends TestCase
         }
     }
 
-    public function testSaveAs()
+    public function testSaveAs(): void
     {
         $tmpImage = UploadedFile::getInstance(new ModelStub(), 'temp_image');
         $targetFile = '@runtime/test_saved_uploaded_file_' . time();
@@ -98,7 +98,7 @@ class UploadedFileTest extends TestCase
         @unlink($targetFile);
     }
 
-    public function testSaveFileFromMultipartFormDataParser()
+    public function testSaveFileFromMultipartFormDataParser(): void
     {
         $_FILES = [];
         UploadedFile::reset();
diff --git a/tests/framework/web/UrlManagerCreateUrlTest.php b/tests/framework/web/UrlManagerCreateUrlTest.php
index a5c0850f88..03a52a9d81 100644
--- a/tests/framework/web/UrlManagerCreateUrlTest.php
+++ b/tests/framework/web/UrlManagerCreateUrlTest.php
@@ -102,7 +102,7 @@ class UrlManagerCreateUrlTest extends TestCase
      * @param string $prefix
      * @param array $config
      */
-    public function testWithoutRules($method, $showScriptName, $prefix, $config)
+    public function testWithoutRules($method, $showScriptName, $prefix, $config): void
     {
         $manager = $this->getUrlManager($config, $showScriptName);
 
@@ -138,7 +138,7 @@ class UrlManagerCreateUrlTest extends TestCase
      * @param string $prefix
      * @param array $config
      */
-    public function testWithoutRulesWithSuffix($method, $showScriptName, $prefix, $config)
+    public function testWithoutRulesWithSuffix($method, $showScriptName, $prefix, $config): void
     {
         $config['suffix'] = '.html';
         $manager = $this->getUrlManager($config, $showScriptName);
@@ -196,7 +196,7 @@ class UrlManagerCreateUrlTest extends TestCase
      * @param string $prefix
      * @param array $config
      */
-    public function testSimpleRules($method, $showScriptName, $prefix, $config)
+    public function testSimpleRules($method, $showScriptName, $prefix, $config): void
     {
         $config['rules'] = [
             'post/<id:\d+>' => 'post/view',
@@ -255,7 +255,7 @@ class UrlManagerCreateUrlTest extends TestCase
      * @param string $prefix
      * @param array $config
      */
-    public function testSimpleRulesWithSuffix($method, $showScriptName, $prefix, $config)
+    public function testSimpleRulesWithSuffix($method, $showScriptName, $prefix, $config): void
     {
         $config['rules'] = [
             'post/<id:\d+>' => 'post/view',
@@ -308,7 +308,7 @@ class UrlManagerCreateUrlTest extends TestCase
      * @param string $prefix
      * @param array $config
      */
-    public function testControllerActionParams($method, $showScriptName, $prefix, $config)
+    public function testControllerActionParams($method, $showScriptName, $prefix, $config): void
     {
         $config['rules'] = [
             '<controller>/<id:\d+>' => '<controller>/view',
@@ -359,7 +359,7 @@ class UrlManagerCreateUrlTest extends TestCase
      * @param string $prefix
      * @param array $config
      */
-    public function testRulesWithDefaultParams($method, $showScriptName, $prefix, $config)
+    public function testRulesWithDefaultParams($method, $showScriptName, $prefix, $config): void
     {
         $config['rules'] = [
             [
@@ -437,7 +437,7 @@ class UrlManagerCreateUrlTest extends TestCase
      * @param string $prefix
      * @param array $config
      */
-    public function testWithNullParams($method, $showScriptName, $prefix, $config)
+    public function testWithNullParams($method, $showScriptName, $prefix, $config): void
     {
         $config['rules'] = [
             '<param1>/<param2>' => 'site/index',
@@ -476,7 +476,7 @@ class UrlManagerCreateUrlTest extends TestCase
      * @param string $prefix
      * @param array $config
      */
-    public function testWithEmptyPattern($method, $showScriptName, $prefix, $config)
+    public function testWithEmptyPattern($method, $showScriptName, $prefix, $config): void
     {
         $assertations = function ($manager) use ($method, $prefix) {
             // match first rule
@@ -546,7 +546,7 @@ class UrlManagerCreateUrlTest extends TestCase
      * @param string $prefix
      * @param array $config
      */
-    public function testAbsolutePatterns($showScriptName, $prefix, $config)
+    public function testAbsolutePatterns($showScriptName, $prefix, $config): void
     {
         $config['rules'] = [
             [
@@ -607,7 +607,7 @@ class UrlManagerCreateUrlTest extends TestCase
      * @param string $prefix
      * @param array $config
      */
-    public function testProtocolRelativeAbsolutePattern($showScriptName, $prefix, $config)
+    public function testProtocolRelativeAbsolutePattern($showScriptName, $prefix, $config): void
     {
         $config['rules'] = [
             [
@@ -699,7 +699,7 @@ class UrlManagerCreateUrlTest extends TestCase
      * @see https://github.com/yiisoft/yii2/issues/7948
      * @param string $host
      */
-    public function testMultipleHostsRules($host)
+    public function testMultipleHostsRules($host): void
     {
         $manager = new UrlManager([
             'enablePrettyUrl' => true,
@@ -726,7 +726,7 @@ class UrlManagerCreateUrlTest extends TestCase
         $this->assertEquals('http://example.fr/search?param1=value1', $url);
     }
 
-    public function testCreateUrlCache()
+    public function testCreateUrlCache(): void
     {
         /** @var CachedUrlRule[] $rules */
         $rules = [
@@ -773,7 +773,7 @@ class UrlManagerCreateUrlTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/pull/1335
      */
-    public function testUrlCreateCacheWithParameterMismatch()
+    public function testUrlCreateCacheWithParameterMismatch(): void
     {
         /** @var CachedUrlRule[] $rules */
         $rules = [
@@ -807,7 +807,7 @@ class UrlManagerCreateUrlTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/14406
      */
-    public function testCreatingRulesWithDifferentRuleConfigAndEnabledCache()
+    public function testCreatingRulesWithDifferentRuleConfigAndEnabledCache(): void
     {
         $this->mockWebApplication([
             'components' => [
@@ -836,7 +836,7 @@ class UrlManagerCreateUrlTest extends TestCase
         $this->assertInstanceOf(CachedUrlRule::className(), $cachedUrlManager->rules[0]);
     }
 
-    public function testNotEnsuringCacheForEmptyRuleset()
+    public function testNotEnsuringCacheForEmptyRuleset(): void
     {
         $this->mockWebApplication([
             'components' => [
diff --git a/tests/framework/web/UrlManagerParseUrlTest.php b/tests/framework/web/UrlManagerParseUrlTest.php
index 7eab079fcb..98c2d156b5 100644
--- a/tests/framework/web/UrlManagerParseUrlTest.php
+++ b/tests/framework/web/UrlManagerParseUrlTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\web;
 
+use yii\web\Application;
 use yii\caching\ArrayCache;
 use yii\web\Request;
 use yii\web\UrlManager;
@@ -72,7 +73,7 @@ class UrlManagerParseUrlTest extends TestCase
         parent::tearDown();
     }
 
-    public function testWithoutRules()
+    public function testWithoutRules(): void
     {
         $manager = $this->getUrlManager();
 
@@ -90,7 +91,7 @@ class UrlManagerParseUrlTest extends TestCase
         $this->assertEquals(['module/site/index/', []], $result);
     }
 
-    public function testWithoutRulesStrict()
+    public function testWithoutRulesStrict(): void
     {
         $manager = $this->getUrlManager();
         $manager->enableStrictParsing = true;
@@ -117,7 +118,7 @@ class UrlManagerParseUrlTest extends TestCase
      * @dataProvider suffixProvider
      * @param string $suffix
      */
-    public function testWithoutRulesWithSuffix($suffix)
+    public function testWithoutRulesWithSuffix($suffix): void
     {
         $manager = $this->getUrlManager(['suffix' => $suffix]);
 
@@ -143,7 +144,7 @@ class UrlManagerParseUrlTest extends TestCase
         $this->assertEquals(['module/site/index/', []], $result);
     }
 
-    public function testSimpleRules()
+    public function testSimpleRules(): void
     {
         $config = [
             'rules' => [
@@ -171,7 +172,7 @@ class UrlManagerParseUrlTest extends TestCase
         $this->assertEquals(['module/site/index', []], $result);
     }
 
-    public function testSimpleRulesStrict()
+    public function testSimpleRulesStrict(): void
     {
         $config = [
             'rules' => [
@@ -204,7 +205,7 @@ class UrlManagerParseUrlTest extends TestCase
      * @dataProvider suffixProvider
      * @param string $suffix
      */
-    public function testSimpleRulesWithSuffix($suffix)
+    public function testSimpleRulesWithSuffix($suffix): void
     {
         $config = [
             'rules' => [
@@ -249,7 +250,7 @@ class UrlManagerParseUrlTest extends TestCase
      * @dataProvider suffixProvider
      * @param string $suffix
      */
-    public function testSimpleRulesWithSuffixStrict($suffix)
+    public function testSimpleRulesWithSuffixStrict($suffix): void
     {
         $config = [
             'rules' => [
@@ -295,7 +296,7 @@ class UrlManagerParseUrlTest extends TestCase
 
     // TODO implement with hostinfo
 
-    public function testParseRESTRequest()
+    public function testParseRESTRequest(): void
     {
         $request = new Request();
 
@@ -340,14 +341,14 @@ class UrlManagerParseUrlTest extends TestCase
                     'baseUrl' => '/app',
                 ],
             ],
-        ], \yii\web\Application::className());
+        ], Application::className());
         $this->assertEquals('/app/post/123', $manager->createUrl(['post/delete', 'id' => 123]));
         $this->destroyApplication();
 
         unset($_SERVER['REQUEST_METHOD']);
     }
 
-    public function testAppendRules()
+    public function testAppendRules(): void
     {
         $manager = $this->getUrlManager(['rules' => ['post/<id:\d+>' => 'post/view']]);
 
@@ -363,7 +364,7 @@ class UrlManagerParseUrlTest extends TestCase
         $this->assertSame($firstRule, $manager->rules[0]);
     }
 
-    public function testPrependRules()
+    public function testPrependRules(): void
     {
         $manager = $this->getUrlManager(['rules' => ['post/<id:\d+>' => 'post/view']]);
 
@@ -380,7 +381,7 @@ class UrlManagerParseUrlTest extends TestCase
         $this->assertSame($firstRule, $manager->rules[2]);
     }
 
-    public function testRulesCache()
+    public function testRulesCache(): void
     {
         $arrayCache = new ArrayCache();
 
@@ -414,7 +415,7 @@ class UrlManagerParseUrlTest extends TestCase
         );
     }
 
-    public function testRulesCacheIsUsed()
+    public function testRulesCacheIsUsed(): void
     {
         $arrayCache = $this->getMockBuilder('yii\caching\ArrayCache')
             ->setMethods(['get', 'set'])
@@ -441,7 +442,7 @@ class UrlManagerParseUrlTest extends TestCase
     /**
      * Test a scenario where catch-all rule is used at the end for a CMS but module names should use the module actions and controllers.
      */
-    public function testModuleRoute()
+    public function testModuleRoute(): void
     {
         $modules = 'user|my-admin';
 
diff --git a/tests/framework/web/UrlManagerTest.php b/tests/framework/web/UrlManagerTest.php
index 15ca7efd88..04726ea00e 100644
--- a/tests/framework/web/UrlManagerTest.php
+++ b/tests/framework/web/UrlManagerTest.php
@@ -77,7 +77,7 @@ class UrlManagerTest extends TestCase
      * @param bool $showScriptName
      * @param bool $enableStrictParsing
      */
-    public function testCreateUrlSimple($showScriptName, $enableStrictParsing)
+    public function testCreateUrlSimple($showScriptName, $enableStrictParsing): void
     {
         // default setting with '/' as base url
         $manager = $this->getUrlManager([], $showScriptName, $enableStrictParsing);
@@ -102,7 +102,7 @@ class UrlManagerTest extends TestCase
      * @param bool $showScriptName
      * @param bool $enableStrictParsing
      */
-    public function testCreateUrlWithParams($showScriptName, $enableStrictParsing)
+    public function testCreateUrlWithParams($showScriptName, $enableStrictParsing): void
     {
         // default setting with '/' as base url
         $manager = $this->getUrlManager([], $showScriptName, $enableStrictParsing);
@@ -125,7 +125,7 @@ class UrlManagerTest extends TestCase
      * @param bool $showScriptName
      * @param bool $enableStrictParsing
      */
-    public function testCreateUrlWithAnchor($showScriptName, $enableStrictParsing)
+    public function testCreateUrlWithAnchor($showScriptName, $enableStrictParsing): void
     {
         // default setting with '/' as base url
         $manager = $this->getUrlManager([], $showScriptName, $enableStrictParsing);
@@ -150,7 +150,7 @@ class UrlManagerTest extends TestCase
      * @param bool $showScriptName
      * @param bool $enableStrictParsing
      */
-    public function testCreateAbsoluteUrl($showScriptName, $enableStrictParsing)
+    public function testCreateAbsoluteUrl($showScriptName, $enableStrictParsing): void
     {
         $manager = $this->getUrlManager([], $showScriptName, $enableStrictParsing);
         $url = $manager->createAbsoluteUrl('post/view');
@@ -198,7 +198,7 @@ class UrlManagerTest extends TestCase
      * @param bool $showScriptName
      * @param bool $enableStrictParsing
      */
-    public function testCreateUrlRouteVariants($showScriptName, $enableStrictParsing)
+    public function testCreateUrlRouteVariants($showScriptName, $enableStrictParsing): void
     {
         // default setting with '/' as base url
         $manager = $this->getUrlManager([], $showScriptName, $enableStrictParsing);
@@ -228,7 +228,7 @@ class UrlManagerTest extends TestCase
      * @dataProvider routeParamProvider
      * @param string $routeParam
      */
-    public function testParseRequest($routeParam)
+    public function testParseRequest($routeParam): void
     {
         $manager = $this->getUrlManager(['routeParam' => $routeParam]);
         $request = new Request();
@@ -255,7 +255,7 @@ class UrlManagerTest extends TestCase
         $this->assertEquals(5, $request->getQueryParam('id'));
     }
 
-    public function testSetBaseUrl()
+    public function testSetBaseUrl(): void
     {
         $manager = $this->getUrlManager();
 
diff --git a/tests/framework/web/UrlNormalizerTest.php b/tests/framework/web/UrlNormalizerTest.php
index af2a8911ff..e5eed7c61f 100644
--- a/tests/framework/web/UrlNormalizerTest.php
+++ b/tests/framework/web/UrlNormalizerTest.php
@@ -27,7 +27,7 @@ class UrlNormalizerTest extends TestCase
         $this->mockApplication();
     }
 
-    public function testNormalizePathInfo()
+    public function testNormalizePathInfo(): void
     {
         $normalizer = new UrlNormalizer();
         $this->assertEquals('post/123/', $normalizer->normalizePathInfo('post//123//', '/a/'));
@@ -54,7 +54,7 @@ class UrlNormalizerTest extends TestCase
         $this->assertEquals('post/123/', $normalizer->normalizePathInfo('post//123//', ''));
     }
 
-    public function testNormalizeRoute()
+    public function testNormalizeRoute(): void
     {
         $normalizer = new UrlNormalizer();
         $route = ['site/index', ['id' => 1, 'name' => 'test']];
@@ -122,7 +122,7 @@ class UrlNormalizerTest extends TestCase
      *
      * Trailing slash is insignificant if normalizer is enabled.
      */
-    public function testUrlManager()
+    public function testUrlManager(): void
     {
         $config = [
             'enablePrettyUrl' => true,
diff --git a/tests/framework/web/UrlRuleTest.php b/tests/framework/web/UrlRuleTest.php
index 2cf31516e8..1d585bec83 100644
--- a/tests/framework/web/UrlRuleTest.php
+++ b/tests/framework/web/UrlRuleTest.php
@@ -29,7 +29,7 @@ class UrlRuleTest extends TestCase
         $this->mockApplication();
     }
 
-    public function testCreateUrl()
+    public function testCreateUrl(): void
     {
         $manager = new UrlManager(['cache' => null]);
         $suites = $this->getTestsForCreateUrl();
@@ -44,7 +44,7 @@ class UrlRuleTest extends TestCase
         }
     }
 
-    public function testParseRequest()
+    public function testParseRequest(): void
     {
         $manager = new UrlManager([
             'cache' => null,
@@ -68,7 +68,7 @@ class UrlRuleTest extends TestCase
         }
     }
 
-    public function testParseRequestWithNormalizer()
+    public function testParseRequestWithNormalizer(): void
     {
         $manager = new UrlManager([
             'cache' => null,
@@ -96,7 +96,7 @@ class UrlRuleTest extends TestCase
         }
     }
 
-    public function testParseRequestWithUrlManagerCustomNormalizer()
+    public function testParseRequestWithUrlManagerCustomNormalizer(): void
     {
         $manager = new UrlManager([
             'cache' => null,
@@ -238,7 +238,7 @@ class UrlRuleTest extends TestCase
         }
     }
 
-    public function testParseRequestWithUrlRuleCustomNormalizer()
+    public function testParseRequestWithUrlRuleCustomNormalizer(): void
     {
         $manager = new UrlManager([
             'cache' => null,
@@ -280,7 +280,7 @@ class UrlRuleTest extends TestCase
         $this->assertEquals(['post/index', ['page' => 1, 'tag' => 'a']], $result);
     }
 
-    public function testToString()
+    public function testToString(): void
     {
         $suites = $this->getTestsForToString();
         foreach ($suites as $i => $suite) {
@@ -1298,7 +1298,7 @@ class UrlRuleTest extends TestCase
      * @param array $config
      * @param array $tests
      */
-    public function testGetCreateUrlStatus($config, $tests)
+    public function testGetCreateUrlStatus($config, $tests): void
     {
         foreach ($tests as $test) {
             list($route, $params, $expected, $status) = $test;
@@ -1321,7 +1321,7 @@ class UrlRuleTest extends TestCase
         }
     }
 
-    public function testUrlRuleDefaultsWithNonStringValues()
+    public function testUrlRuleDefaultsWithNonStringValues(): void
     {
         $this->mockWebApplication();
 
diff --git a/tests/framework/web/UserTest.php b/tests/framework/web/UserTest.php
index 26650bd078..98c3e7cc6e 100644
--- a/tests/framework/web/UserTest.php
+++ b/tests/framework/web/UserTest.php
@@ -46,7 +46,7 @@ class UserTest extends TestCase
         parent::tearDown();
     }
 
-    public function testLoginExpires()
+    public function testLoginExpires(): void
     {
         $appConfig = [
             'components' => [
@@ -97,7 +97,7 @@ class UserTest extends TestCase
      * Make sure autologin works more than once.
      * @see https://github.com/yiisoft/yii2/issues/11825
      */
-    public function testIssue11825()
+    public function testIssue11825(): void
     {
         global $cookiesMock;
         $cookiesMock = new CookieCollection();
@@ -148,7 +148,7 @@ class UserTest extends TestCase
         $this->assertTrue(Yii::$app->user->isGuest);
     }
 
-    public function testCookieCleanup()
+    public function testCookieCleanup(): void
     {
         global $cookiesMock;
 
@@ -217,7 +217,7 @@ class UserTest extends TestCase
         Yii::$app->user->setReturnUrl(null);
     }
 
-    public function testLoginRequired()
+    public function testLoginRequired(): void
     {
         $appConfig = [
             'components' => [
@@ -343,7 +343,7 @@ class UserTest extends TestCase
         $this->assertSame($id, Yii::$app->session->id);
     }
 
-    public function testLoginRequiredException1()
+    public function testLoginRequiredException1(): void
     {
         $appConfig = [
             'components' => [
@@ -366,7 +366,7 @@ class UserTest extends TestCase
         Yii::$app->user->loginRequired();
     }
 
-    public function testAccessChecker()
+    public function testAccessChecker(): void
     {
         $this->mockWebApplication([
             'components' => [
@@ -404,7 +404,7 @@ class UserTest extends TestCase
         $this->assertInstanceOf(AccessChecker::className(), Yii::$app->user->accessChecker);
     }
 
-    public function testGetIdentityException()
+    public function testGetIdentityException(): void
     {
         $session = $this->getMockBuilder(\yii\web\Session::class)->getMock();
         $session->method('getHasSessionId')->willReturn(true);
@@ -433,7 +433,7 @@ class UserTest extends TestCase
         Yii::$app->getUser()->getIdentity();
     }
 
-    public function testSetIdentity()
+    public function testSetIdentity(): void
     {
         $appConfig = [
             'components' => [
@@ -472,7 +472,7 @@ class UserTest extends TestCase
         Yii::$app->user->setIdentity(new \stdClass());
     }
 
-    public function testSessionAuthWithNonExistingId()
+    public function testSessionAuthWithNonExistingId(): void
     {
         $appConfig = [
             'components' => [
@@ -489,7 +489,7 @@ class UserTest extends TestCase
         $this->assertNull(Yii::$app->user->getIdentity());
     }
 
-    public function testSessionAuthWithMissingKey()
+    public function testSessionAuthWithMissingKey(): void
     {
         $appConfig = [
             'components' => [
@@ -508,7 +508,7 @@ class UserTest extends TestCase
         $this->assertSame($id, Yii::$app->session->id);
     }
 
-    public function testSessionAuthWithInvalidKey()
+    public function testSessionAuthWithInvalidKey(): void
     {
         $appConfig = [
             'components' => [
@@ -528,7 +528,7 @@ class UserTest extends TestCase
         $this->assertSame($id, Yii::$app->session->id);
     }
 
-    public function testSessionAuthWithValidKey()
+    public function testSessionAuthWithValidKey(): void
     {
         $appConfig = [
             'components' => [
@@ -548,7 +548,7 @@ class UserTest extends TestCase
         $this->assertSame($id, Yii::$app->session->id);
     }
 
-    public function testSessionAuthWhenIdentityReturnsNull()
+    public function testSessionAuthWhenIdentityReturnsNull(): void
     {
         $appConfig = [
             'components' => [
@@ -593,7 +593,7 @@ class MockResponse extends \yii\web\Response
 
 class AccessChecker extends BaseObject implements CheckAccessInterface
 {
-    public function checkAccess($userId, $permissionName, $params = [])
+    public function checkAccess($userId, $permissionName, $params = []): void
     {
         // Implement checkAccess() method.
     }
diff --git a/tests/framework/web/ViewTest.php b/tests/framework/web/ViewTest.php
index c367eec0cc..f63d95c950 100644
--- a/tests/framework/web/ViewTest.php
+++ b/tests/framework/web/ViewTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\web;
 
+use Yii;
 use yii\caching\FileCache;
 use yii\web\View;
 use yiiunit\TestCase;
@@ -22,7 +23,7 @@ class ViewTest extends TestCase
         parent::setUp();
     }
 
-    public function testRegisterJsVar()
+    public function testRegisterJsVar(): void
     {
         $this->mockWebApplication([
             'components' => [
@@ -53,7 +54,7 @@ class ViewTest extends TestCase
         );
     }
 
-    public function testRegisterJsFileWithAlias()
+    public function testRegisterJsFileWithAlias(): void
     {
         $this->mockWebApplication([
             'components' => [
@@ -86,7 +87,7 @@ class ViewTest extends TestCase
         $this->assertStringContainsString('<script src="/baseUrl/js/somefile.js"></script></body>', $html);
     }
 
-    public function testRegisterCssFileWithAlias()
+    public function testRegisterCssFileWithAlias(): void
     {
         $this->mockWebApplication([
             'components' => [
@@ -112,7 +113,7 @@ class ViewTest extends TestCase
         $this->assertStringContainsString('<link href="/baseUrl/css/somefile.css" rel="stylesheet"></head>', $html);
     }
 
-    public function testRegisterregisterCsrfMetaTags()
+    public function testRegisterregisterCsrfMetaTags(): void
     {
         $this->mockWebApplication([
             'components' => [
@@ -135,7 +136,7 @@ class ViewTest extends TestCase
         $csrfToken1 = $this->getCSRFTokenValue($html);
 
         // regenerate token
-        \Yii::$app->request->getCsrfToken(true);
+        Yii::$app->request->getCsrfToken(true);
         $view->registerCsrfMetaTags();
         $html = $view->render('@yiiunit/data/views/layout.php', ['content' => 'content']);
         $this->assertStringContainsString('<meta name="csrf-param" content="_csrf">', $html);
@@ -160,16 +161,16 @@ class ViewTest extends TestCase
         return $matches[1];
     }
 
-    private function setUpAliases()
+    private function setUpAliases(): void
     {
-        \Yii::setAlias('@web', '/');
-        \Yii::setAlias('@webroot', '@yiiunit/data/web');
-        \Yii::setAlias('@testAssetsPath', '@webroot/assets');
-        \Yii::setAlias('@testAssetsUrl', '@web/assets');
-        \Yii::setAlias('@testSourcePath', '@webroot/assetSources');
+        Yii::setAlias('@web', '/');
+        Yii::setAlias('@webroot', '@yiiunit/data/web');
+        Yii::setAlias('@testAssetsPath', '@webroot/assets');
+        Yii::setAlias('@testAssetsUrl', '@web/assets');
+        Yii::setAlias('@testSourcePath', '@webroot/assetSources');
     }
 
-    public function testAppendTimestampForRegisterJsFile()
+    public function testAppendTimestampForRegisterJsFile(): void
     {
         $this->mockWebApplication([
             'components' => [
@@ -184,7 +185,7 @@ class ViewTest extends TestCase
 
         $pattern = '/assetSources\/js\/jquery\.js\?v\=\d+"/';
 
-        \Yii::$app->assetManager->appendTimestamp = true;
+        Yii::$app->assetManager->appendTimestamp = true;
 
         // will be used AssetManager and timestamp
         $view = new View();
@@ -196,20 +197,20 @@ class ViewTest extends TestCase
         $this->assertMatchesRegularExpression($pattern, $html);
 
         // test append timestamp when @web is prefixed in url
-        \Yii::setAlias('@web', '/test-app');
+        Yii::setAlias('@web', '/test-app');
         $view = new View();
         $view->registerJsFile(
-            \Yii::getAlias('@web/assetSources/js/jquery.js'),
+            Yii::getAlias('@web/assetSources/js/jquery.js'),
             ['depends' => 'yii\web\AssetBundle']
         ); // <script src="/assetSources/js/jquery.js?v=1541056962"></script>
         $html = $view->render('@yiiunit/data/views/layout.php', ['content' => 'content']);
         $this->assertMatchesRegularExpression($pattern, $html);
 
         // test append timestamp when @web has the same name as the asset-source folder
-        \Yii::setAlias('@web', '/assetSources/');
+        Yii::setAlias('@web', '/assetSources/');
         $view = new View();
         $view->registerJsFile(
-            \Yii::getAlias('@web/assetSources/js/jquery.js'),
+            Yii::getAlias('@web/assetSources/js/jquery.js'),
             ['depends' => 'yii\web\AssetBundle']
         ); // <script src="/assetSources/js/jquery.js?v=1541056962"></script>
         $html = $view->render('@yiiunit/data/views/layout.php', ['content' => 'content']);
@@ -299,7 +300,7 @@ class ViewTest extends TestCase
             $html
         );
 
-        \Yii::$app->assetManager->appendTimestamp = false;
+        Yii::$app->assetManager->appendTimestamp = false;
 
         $view = new View();
         $view->registerJsFile(
@@ -374,7 +375,7 @@ class ViewTest extends TestCase
         );
     }
 
-    public function testAppendTimestampForRegisterCssFile()
+    public function testAppendTimestampForRegisterCssFile(): void
     {
         $this->mockWebApplication([
             'components' => [
@@ -389,7 +390,7 @@ class ViewTest extends TestCase
 
         $pattern = '/assetSources\/css\/stub\.css\?v\=\d+"/';
 
-        \Yii::$app->assetManager->appendTimestamp = true;
+        Yii::$app->assetManager->appendTimestamp = true;
 
         // will be used AssetManager and timestamp
         $view = new View();
@@ -401,20 +402,20 @@ class ViewTest extends TestCase
         $this->assertMatchesRegularExpression($pattern, $html);
 
         // test append timestamp when @web is prefixed in url
-        \Yii::setAlias('@web', '/test-app');
+        Yii::setAlias('@web', '/test-app');
         $view = new View();
         $view->registerCssFile(
-            \Yii::getAlias('@web/assetSources/css/stub.css'),
+            Yii::getAlias('@web/assetSources/css/stub.css'),
             ['depends' => 'yii\web\AssetBundle']
         ); // <link href="/assetSources/css/stub.css?v=1541056962" rel="stylesheet" >
         $html = $view->render('@yiiunit/data/views/layout.php', ['content' => 'content']);
         $this->assertMatchesRegularExpression($pattern, $html);
 
         // test append timestamp when @web has the same name as the asset-source folder
-        \Yii::setAlias('@web', '/assetSources/');
+        Yii::setAlias('@web', '/assetSources/');
         $view = new View();
         $view->registerCssFile(
-            \Yii::getAlias('@web/assetSources/css/stub.css'),
+            Yii::getAlias('@web/assetSources/css/stub.css'),
             ['depends' => 'yii\web\AssetBundle']
         ); // <link href="/assetSources/css/stub.css?v=1541056962" rel="stylesheet" >
         $html = $view->render('@yiiunit/data/views/layout.php', ['content' => 'content']);
@@ -504,7 +505,7 @@ class ViewTest extends TestCase
             $html
         );
 
-        \Yii::$app->assetManager->appendTimestamp = false;
+        Yii::$app->assetManager->appendTimestamp = false;
 
         $view = new View();
         $view->registerCssFile(
diff --git a/tests/framework/web/XmlResponseFormatterTest.php b/tests/framework/web/XmlResponseFormatterTest.php
index 90f64e84ea..3ff9b15423 100644
--- a/tests/framework/web/XmlResponseFormatterTest.php
+++ b/tests/framework/web/XmlResponseFormatterTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\web;
 
+use SplStack;
 use yii\web\XmlResponseFormatter;
 use yiiunit\framework\web\stubs\ModelStub;
 
@@ -93,7 +94,7 @@ class XmlResponseFormatterTest extends FormatterTest
     {
         $expectedXmlForStack = '';
 
-        $postsStack = new \SplStack();
+        $postsStack = new SplStack();
 
         $postsStack->push(new Post(915, 'record1'));
         $expectedXmlForStack = '<Post><id>915</id><title>record1</title></Post>' .
@@ -135,7 +136,7 @@ class XmlResponseFormatterTest extends FormatterTest
         ]);
     }
 
-    public function testCustomRootTag()
+    public function testCustomRootTag(): void
     {
         $rootTag = 'custom';
         $formatter = $this->getFormatterInstance([
@@ -147,7 +148,7 @@ class XmlResponseFormatterTest extends FormatterTest
         $this->assertEquals($this->xmlHead . "<$rootTag>1</$rootTag>\n", $this->response->content);
     }
 
-    public function testRootTagRemoval()
+    public function testRootTagRemoval(): void
     {
         $formatter = $this->getFormatterInstance([
             'rootTag' => null,
@@ -158,7 +159,7 @@ class XmlResponseFormatterTest extends FormatterTest
         $this->assertEquals($this->xmlHead . "1\n", $this->response->content);
     }
 
-    public function testNoObjectTags()
+    public function testNoObjectTags(): void
     {
         $formatter = $this->getFormatterInstance([
             'useObjectTags' => false,
@@ -169,7 +170,7 @@ class XmlResponseFormatterTest extends FormatterTest
         $this->assertEquals($this->xmlHead . "<response><id>123</id><title>abc</title></response>\n", $this->response->content);
     }
 
-    public function testObjectTagToLowercase()
+    public function testObjectTagToLowercase(): void
     {
         $formatter = $this->getFormatterInstance(['objectTagToLowercase' => true]);
 
diff --git a/tests/framework/web/session/AbstractDbSessionTest.php b/tests/framework/web/session/AbstractDbSessionTest.php
index e88122b805..5db7b15060 100644
--- a/tests/framework/web/session/AbstractDbSessionTest.php
+++ b/tests/framework/web/session/AbstractDbSessionTest.php
@@ -8,6 +8,9 @@
 
 namespace yiiunit\framework\web\session;
 
+use PDO;
+use Exception;
+use stdClass;
 use Yii;
 use yii\db\Connection;
 use yii\db\Migration;
@@ -49,7 +52,7 @@ abstract class AbstractDbSessionTest extends TestCase
         $driverNames = $this->getDriverNames();
         $databases = self::getParam('databases');
         foreach ($driverNames as $driverName) {
-            if (in_array($driverName, \PDO::getAvailableDrivers()) && array_key_exists($driverName, $databases)) {
+            if (in_array($driverName, PDO::getAvailableDrivers()) && array_key_exists($driverName, $databases)) {
                 $driverAvailable = $driverName;
                 break;
             }
@@ -84,7 +87,7 @@ abstract class AbstractDbSessionTest extends TestCase
     {
         try {
             $this->runMigrate('down', ['all']);
-        } catch (\Exception $e) {
+        } catch (Exception $e) {
             // Table may not exist for different reasons, but since this method
             // reverts DB changes to make next test pass, this exception is skipped.
         }
@@ -92,7 +95,7 @@ abstract class AbstractDbSessionTest extends TestCase
 
     // Tests :
 
-    public function testReadWrite()
+    public function testReadWrite(): void
     {
         $session = new DbSession();
 
@@ -102,7 +105,7 @@ abstract class AbstractDbSessionTest extends TestCase
         $this->assertEquals('', $session->readSession('test'));
     }
 
-    public function testInitializeWithConfig()
+    public function testInitializeWithConfig(): void
     {
         // should produce no exceptions
         $session = new DbSession([
@@ -118,7 +121,7 @@ abstract class AbstractDbSessionTest extends TestCase
     /**
      * @depends testReadWrite
      */
-    public function testGarbageCollection()
+    public function testGarbageCollection(): void
     {
         $session = new DbSession();
 
@@ -138,7 +141,7 @@ abstract class AbstractDbSessionTest extends TestCase
     /**
      * @depends testReadWrite
      */
-    public function testWriteCustomField()
+    public function testWriteCustomField(): void
     {
         $session = new DbSession();
 
@@ -155,7 +158,7 @@ abstract class AbstractDbSessionTest extends TestCase
     /**
      * @depends testReadWrite
      */
-    public function testWriteCustomFieldWithUserId()
+    public function testWriteCustomFieldWithUserId(): void
     {
         $session = new DbSession();
         $session->open();
@@ -182,7 +185,7 @@ abstract class AbstractDbSessionTest extends TestCase
 
     protected function buildObjectForSerialization()
     {
-        $object = new \stdClass();
+        $object = new stdClass();
         $object->nullValue = null;
         $object->floatValue = pi();
         $object->textValue = str_repeat('Qweå߃Тест', 200);
@@ -198,7 +201,7 @@ abstract class AbstractDbSessionTest extends TestCase
         return $object;
     }
 
-    public function testSerializedObjectSaving()
+    public function testSerializedObjectSaving(): void
     {
         $session = new DbSession();
 
@@ -230,7 +233,7 @@ abstract class AbstractDbSessionTest extends TestCase
         }, (new Query())->select(['version'])->from('migration')->column());
     }
 
-    public function testMigration()
+    public function testMigration(): void
     {
         $this->dropTableSession();
         $this->mockWebApplication([
@@ -250,7 +253,7 @@ abstract class AbstractDbSessionTest extends TestCase
         $this->createTableSession();
     }
 
-    public function testInstantiate()
+    public function testInstantiate(): void
     {
         $oldTimeout = ini_get('session.gc_maxlifetime');
         // unset Yii::$app->db to make sure that all queries are made against sessionDb
@@ -271,12 +274,12 @@ abstract class AbstractDbSessionTest extends TestCase
         ini_set('session.gc_maxlifetime', $oldTimeout);
     }
 
-    public function testInitUseStrictMode()
+    public function testInitUseStrictMode(): void
     {
         $this->initStrictModeTest(DbSession::className());
     }
 
-    public function testUseStrictMode()
+    public function testUseStrictMode(): void
     {
         $this->useStrictModeTest(DbSession::className());
     }
diff --git a/tests/framework/web/session/CacheSessionTest.php b/tests/framework/web/session/CacheSessionTest.php
index f8cbee55b8..e8e2b735ac 100644
--- a/tests/framework/web/session/CacheSessionTest.php
+++ b/tests/framework/web/session/CacheSessionTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\web\session;
 
+use yiiunit\TestCase;
 use Yii;
 use yii\caching\FileCache;
 use yii\web\CacheSession;
@@ -15,7 +16,7 @@ use yii\web\CacheSession;
 /**
  * @group web
  */
-class CacheSessionTest extends \yiiunit\TestCase
+class CacheSessionTest extends TestCase
 {
     use SessionTestTrait;
 
@@ -26,7 +27,7 @@ class CacheSessionTest extends \yiiunit\TestCase
         Yii::$app->set('cache', new FileCache());
     }
 
-    public function testCacheSession()
+    public function testCacheSession(): void
     {
         $session = new CacheSession();
 
@@ -36,7 +37,7 @@ class CacheSessionTest extends \yiiunit\TestCase
         $this->assertEquals('', $session->readSession('test'));
     }
 
-    public function testInvalidCache()
+    public function testInvalidCache(): void
     {
         $this->expectException('\Exception');
         new CacheSession(['cache' => 'invalid']);
@@ -45,7 +46,7 @@ class CacheSessionTest extends \yiiunit\TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/13537
      */
-    public function testNotWrittenSessionDestroying()
+    public function testNotWrittenSessionDestroying(): void
     {
         $session = new CacheSession();
 
@@ -55,12 +56,12 @@ class CacheSessionTest extends \yiiunit\TestCase
         $this->assertTrue($session->destroySession($session->getId()));
     }
 
-    public function testInitUseStrictMode()
+    public function testInitUseStrictMode(): void
     {
         $this->initStrictModeTest(CacheSession::className());
     }
 
-    public function testUseStrictMode()
+    public function testUseStrictMode(): void
     {
         $this->useStrictModeTest(CacheSession::className());
     }
diff --git a/tests/framework/web/session/SessionTest.php b/tests/framework/web/session/SessionTest.php
index 978eab69e5..9bdb129c92 100644
--- a/tests/framework/web/session/SessionTest.php
+++ b/tests/framework/web/session/SessionTest.php
@@ -21,7 +21,7 @@ class SessionTest extends TestCase
     /**
      * Test to prove that after Session::destroy session id set to old value.
      */
-    public function testDestroySessionId()
+    public function testDestroySessionId(): void
     {
         $session = new Session();
         $session->open();
@@ -40,7 +40,7 @@ class SessionTest extends TestCase
      * Test to prove that after Session::open changing session parameters will not throw exceptions
      * and its values will be changed as expected.
      */
-    public function testParamsAfterSessionStart()
+    public function testParamsAfterSessionStart(): void
     {
         $session = new Session();
         $session->open();
@@ -84,7 +84,7 @@ class SessionTest extends TestCase
     /**
      * Test set name. Also check set name twice and after open
      */
-    public function testSetName()
+    public function testSetName(): void
     {
         $session = new Session();
         $session->setName('oldName');
@@ -99,12 +99,12 @@ class SessionTest extends TestCase
         $session->destroy();
     }
 
-    public function testInitUseStrictMode()
+    public function testInitUseStrictMode(): void
     {
         $this->initStrictModeTest(Session::className());
     }
 
-    public function testUseStrictMode()
+    public function testUseStrictMode(): void
     {
         //Manual garbage collection since native storage module might not support removing data via Session::destroySession()
         $sessionSavePath = session_save_path() ?: sys_get_temp_dir();
diff --git a/tests/framework/web/session/SessionTestTrait.php b/tests/framework/web/session/SessionTestTrait.php
index 03797cdd33..c8684f6178 100644
--- a/tests/framework/web/session/SessionTestTrait.php
+++ b/tests/framework/web/session/SessionTestTrait.php
@@ -6,7 +6,7 @@ use yii\web\Session;
 
 trait SessionTestTrait
 {
-    public function initStrictModeTest($class)
+    public function initStrictModeTest($class): void
     {
         /** @var Session $session */
         $session = new $class();
diff --git a/tests/framework/web/session/mssql/DbSessionTest.php b/tests/framework/web/session/mssql/DbSessionTest.php
index 2efe514b82..c77a053e30 100644
--- a/tests/framework/web/session/mssql/DbSessionTest.php
+++ b/tests/framework/web/session/mssql/DbSessionTest.php
@@ -8,6 +8,8 @@
 
 namespace yiiunit\framework\web\session\mssql;
 
+use yiiunit\framework\web\session\AbstractDbSessionTest;
+
 /**
  * Class DbSessionTest.
  *
@@ -16,7 +18,7 @@ namespace yiiunit\framework\web\session\mssql;
  * @group db
  * @group mssql
  */
-class DbSessionTest extends \yiiunit\framework\web\session\AbstractDbSessionTest
+class DbSessionTest extends AbstractDbSessionTest
 {
     protected function getDriverNames()
     {
diff --git a/tests/framework/web/session/mysql/DbSessionTest.php b/tests/framework/web/session/mysql/DbSessionTest.php
index 049320fcd5..a55aa5539b 100644
--- a/tests/framework/web/session/mysql/DbSessionTest.php
+++ b/tests/framework/web/session/mysql/DbSessionTest.php
@@ -8,6 +8,8 @@
 
 namespace yiiunit\framework\web\session\mysql;
 
+use yiiunit\framework\web\session\AbstractDbSessionTest;
+
 /**
  * Class DbSessionTest.
  *
@@ -16,7 +18,7 @@ namespace yiiunit\framework\web\session\mysql;
  * @group db
  * @group mysql
  */
-class DbSessionTest extends \yiiunit\framework\web\session\AbstractDbSessionTest
+class DbSessionTest extends AbstractDbSessionTest
 {
     protected function getDriverNames()
     {
diff --git a/tests/framework/web/session/pgsql/DbSessionTest.php b/tests/framework/web/session/pgsql/DbSessionTest.php
index ded86213d1..e1f22941b5 100644
--- a/tests/framework/web/session/pgsql/DbSessionTest.php
+++ b/tests/framework/web/session/pgsql/DbSessionTest.php
@@ -8,6 +8,8 @@
 
 namespace yiiunit\framework\web\session\pgsql;
 
+use yiiunit\framework\web\session\AbstractDbSessionTest;
+
 /**
  * Class DbSessionTest.
  *
@@ -16,7 +18,7 @@ namespace yiiunit\framework\web\session\pgsql;
  * @group db
  * @group pgsql
  */
-class DbSessionTest extends \yiiunit\framework\web\session\AbstractDbSessionTest
+class DbSessionTest extends AbstractDbSessionTest
 {
     protected function setUp(): void
     {
diff --git a/tests/framework/web/session/sqlite/DbSessionTest.php b/tests/framework/web/session/sqlite/DbSessionTest.php
index f4e973af9c..9c0a8be44e 100644
--- a/tests/framework/web/session/sqlite/DbSessionTest.php
+++ b/tests/framework/web/session/sqlite/DbSessionTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\web\session\sqlite;
 
+use yiiunit\framework\web\session\AbstractDbSessionTest;
 use Yii;
 
 /**
@@ -18,7 +19,7 @@ use Yii;
  * @group db
  * @group sqlite
  */
-class DbSessionTest extends \yiiunit\framework\web\session\AbstractDbSessionTest
+class DbSessionTest extends AbstractDbSessionTest
 {
     protected function setUp(): void
     {
diff --git a/tests/framework/widgets/ActiveFieldTest.php b/tests/framework/widgets/ActiveFieldTest.php
index 188adbcc4c..25d11c172e 100644
--- a/tests/framework/widgets/ActiveFieldTest.php
+++ b/tests/framework/widgets/ActiveFieldTest.php
@@ -8,6 +8,9 @@
 
 namespace yiiunit\framework\widgets;
 
+use yiiunit\TestCase;
+use Exception;
+use yii\validators\Validator;
 use DMS\PHPUnitExtensions\ArraySubset\ArraySubsetAsserts;
 use Yii;
 use yii\base\DynamicModel;
@@ -23,7 +26,7 @@ use yii\widgets\MaskedInput;
  *
  * @group widgets
  */
-class ActiveFieldTest extends \yiiunit\TestCase
+class ActiveFieldTest extends TestCase
 {
     use ArraySubsetAsserts;
 
@@ -66,7 +69,7 @@ class ActiveFieldTest extends \yiiunit\TestCase
         $this->activeField->attribute = $this->attributeName;
     }
 
-    public function testRenderNoContent()
+    public function testRenderNoContent(): void
     {
         $expectedValue = <<<EOD
 <div class="form-group field-activefieldtestmodel-attributename">
@@ -84,7 +87,7 @@ EOD;
     /**
      * @todo discuss|review Expected HTML shouldn't be wrapped only by the $content?
      */
-    public function testRenderWithCallableContent()
+    public function testRenderWithCallableContent(): void
     {
         // field will be the html of the model's attribute wrapped with the return string below.
         $field = $this->attributeName;
@@ -110,7 +113,7 @@ EOD;
     /**
      * @link https://github.com/yiisoft/yii2/issues/7627
      */
-    public function testRenderWithCustomInputId()
+    public function testRenderWithCustomInputId(): void
     {
         $expectedValue = <<<EOD
 <div class="form-group field-custom-input-id">
@@ -127,7 +130,7 @@ EOD;
         $this->assertEqualsWithoutLE($expectedValue, $actualValue);
     }
 
-    public function testBeginHasErrors()
+    public function testBeginHasErrors(): void
     {
         $this->helperModel->addError($this->attributeName, 'Error Message');
 
@@ -137,7 +140,7 @@ EOD;
         $this->assertEquals($expectedValue, $actualValue);
     }
 
-    public function testBeginAttributeIsRequired()
+    public function testBeginAttributeIsRequired(): void
     {
         $this->helperModel->addRule($this->attributeName, 'required');
 
@@ -147,7 +150,7 @@ EOD;
         $this->assertEquals($expectedValue, $actualValue);
     }
 
-    public function testBeginHasErrorAndRequired()
+    public function testBeginHasErrorAndRequired(): void
     {
         $this->helperModel->addError($this->attributeName, 'Error Message');
         $this->helperModel->addRule($this->attributeName, 'required');
@@ -158,7 +161,7 @@ EOD;
         $this->assertEquals($expectedValue, $actualValue);
     }
 
-    public function testBegin()
+    public function testBegin(): void
     {
         $expectedValue = '<article class="form-group field-activefieldtestmodel-attributename">';
         $this->activeField->options['tag'] = 'article';
@@ -179,7 +182,7 @@ EOD;
         $this->assertEquals($expectedValue, $actualValue);
     }
 
-    public function testEnd()
+    public function testEnd(): void
     {
         $expectedValue = '</div>';
         $actualValue = $this->activeField->end();
@@ -206,7 +209,7 @@ EOD;
         $this->assertEquals($expectedValue, $actualValue);
     }
 
-    public function testLabel()
+    public function testLabel(): void
     {
         $expectedValue = '<label class="control-label" for="activefieldtestmodel-attributename">Attribute Name</label>';
         $this->activeField->label();
@@ -229,7 +232,7 @@ EOT;
         $this->assertEquals($expectedValue, $this->activeField->parts['{label}']);
     }
 
-    public function testError()
+    public function testError(): void
     {
         $expectedValue = '<label class="control-label" for="activefieldtestmodel-attributename">Attribute Name</label>';
         $this->activeField->label();
@@ -252,7 +255,7 @@ EOT;
         $this->assertEquals($expectedValue, $this->activeField->parts['{label}']);
     }
 
-    public function testTabularInputErrors()
+    public function testTabularInputErrors(): void
     {
         $this->activeField->attribute = '[0]' . $this->attributeName;
         $this->helperModel->addError($this->attributeName, 'Error Message');
@@ -277,14 +280,14 @@ EOT;
      * @param mixed $hint
      * @param string $expectedHtml
      */
-    public function testHint($hint, $expectedHtml)
+    public function testHint($hint, $expectedHtml): void
     {
         $this->activeField->hint($hint);
 
         $this->assertEquals($expectedHtml, $this->activeField->parts['{hint}']);
     }
 
-    public function testInput()
+    public function testInput(): void
     {
         $expectedValue = <<<'EOD'
 <input type="password" id="activefieldtestmodel-attributename" class="form-control" name="ActiveFieldTestModel[attributeName]">
@@ -302,7 +305,7 @@ EOD;
         $this->assertEquals($expectedValue, $this->activeField->parts['{input}']);
     }
 
-    public function testTextInput()
+    public function testTextInput(): void
     {
         $expectedValue = <<<'EOD'
 <input type="text" id="activefieldtestmodel-attributename" class="form-control" name="ActiveFieldTestModel[attributeName]">
@@ -311,7 +314,7 @@ EOD;
         $this->assertEquals($expectedValue, $this->activeField->parts['{input}']);
     }
 
-    public function testHiddenInput()
+    public function testHiddenInput(): void
     {
         $expectedValue = <<<'EOD'
 <input type="hidden" id="activefieldtestmodel-attributename" class="form-control" name="ActiveFieldTestModel[attributeName]">
@@ -320,7 +323,7 @@ EOD;
         $this->assertEquals($expectedValue, $this->activeField->parts['{input}']);
     }
 
-    public function testListBox()
+    public function testListBox(): void
     {
         $expectedValue = <<<'EOD'
 <input type="hidden" name="ActiveFieldTestModel[attributeName]" value=""><select id="activefieldtestmodel-attributename" class="form-control" name="ActiveFieldTestModel[attributeName]" size="4">
@@ -358,7 +361,7 @@ EOD;
         $this->assertEqualsWithoutLE($expectedValue, $this->activeField->parts['{input}']);
     }
 
-    public function testRadioList()
+    public function testRadioList(): void
     {
         $expectedValue = <<<'EOD'
 <div class="form-group field-activefieldtestmodel-attributename">
@@ -372,7 +375,7 @@ EOD;
         $this->assertEqualsWithoutLE($expectedValue, $this->activeField->render());
     }
 
-    public function testGetClientOptionsReturnEmpty()
+    public function testGetClientOptionsReturnEmpty(): void
     {
         // setup: we want the real deal here!
         $this->activeField->setClientOptionsEmpty(false);
@@ -382,7 +385,7 @@ EOD;
         $this->assertEmpty($actualValue);
     }
 
-    public function testGetClientOptionsWithActiveAttributeInScenario()
+    public function testGetClientOptionsWithActiveAttributeInScenario(): void
     {
         $this->activeField->setClientOptionsEmpty(false);
 
@@ -394,7 +397,7 @@ EOD;
         $this->assertEmpty($actualValue);
     }
 
-    public function testGetClientOptionsClientValidation()
+    public function testGetClientOptionsClientValidation(): void
     {
         $this->activeField->setClientOptionsEmpty(false);
 
@@ -425,7 +428,7 @@ EOD;
         $this->assertSame($expectedEnableAjaxValidation, $actualValue['enableAjaxValidation']);
     }
 
-    public function testGetClientOptionsValidatorWhenClientSet()
+    public function testGetClientOptionsValidatorWhenClientSet(): void
     {
         $this->activeField->setClientOptionsEmpty(false);
         $this->activeField->enableAjaxValidation = true;
@@ -445,7 +448,7 @@ EOD;
     /**
      * @see https://github.com/yiisoft/yii2/issues/8779
      */
-    public function testEnctype()
+    public function testEnctype(): void
     {
         $this->activeField->fileInput();
         $this->assertEquals('multipart/form-data', $this->activeField->form->options['enctype']);
@@ -454,7 +457,7 @@ EOD;
     /**
      * @link https://github.com/yiisoft/yii2/issues/7627
      */
-    public function testGetClientOptionsWithCustomInputId()
+    public function testGetClientOptionsWithCustomInputId(): void
     {
         $this->activeField->setClientOptionsEmpty(false);
 
@@ -481,7 +484,7 @@ EOD;
         ], $actualValue);
     }
 
-    public function testAriaAttributes()
+    public function testAriaAttributes(): void
     {
         $this->activeField->addAriaAttributes = true;
 
@@ -498,7 +501,7 @@ EOD;
         $this->assertEqualsWithoutLE($expectedValue, $actualValue);
     }
 
-    public function testAriaRequiredAttribute()
+    public function testAriaRequiredAttribute(): void
     {
         $this->activeField->addAriaAttributes = true;
         $this->helperModel->addRule([$this->attributeName], 'required');
@@ -516,7 +519,7 @@ EOD;
         $this->assertEqualsWithoutLE($expectedValue, $actualValue);
     }
 
-    public function testAriaInvalidAttribute()
+    public function testAriaInvalidAttribute(): void
     {
         $this->activeField->addAriaAttributes = true;
         $this->helperModel->addError($this->attributeName, 'Some error');
@@ -534,7 +537,7 @@ EOD;
         $this->assertEqualsWithoutLE($expectedValue, $actualValue);
     }
 
-    public function testTabularAriaAttributes()
+    public function testTabularAriaAttributes(): void
     {
         $this->activeField->attribute = '[0]' . $this->attributeName;
         $this->activeField->addAriaAttributes = true;
@@ -552,7 +555,7 @@ EOD;
         $this->assertEqualsWithoutLE($expectedValue, $actualValue);
     }
 
-    public function testTabularAriaRequiredAttribute()
+    public function testTabularAriaRequiredAttribute(): void
     {
         $this->activeField->attribute = '[0]' . $this->attributeName;
         $this->activeField->addAriaAttributes = true;
@@ -571,7 +574,7 @@ EOD;
         $this->assertEqualsWithoutLE($expectedValue, $actualValue);
     }
 
-    public function testTabularAriaInvalidAttribute()
+    public function testTabularAriaInvalidAttribute(): void
     {
         $this->activeField->attribute = '[0]' . $this->attributeName;
         $this->activeField->addAriaAttributes = true;
@@ -590,7 +593,7 @@ EOD;
         $this->assertEqualsWithoutLE($expectedValue, $actualValue);
     }
 
-    public function testEmptyTag()
+    public function testEmptyTag(): void
     {
         $this->activeField->options = ['tag' => false];
         $expectedValue = '<input type="hidden" id="activefieldtestmodel-attributename" class="form-control" name="ActiveFieldTestModel[attributeName]">';
@@ -598,7 +601,7 @@ EOD;
         $this->assertEqualsWithoutLE($expectedValue, trim($actualValue));
     }
 
-    public function testWidget()
+    public function testWidget(): void
     {
         $this->activeField->widget(TestInputWidget::className());
         $this->assertEquals('Render: ' . TestInputWidget::className(), $this->activeField->parts['{input}']);
@@ -613,7 +616,7 @@ EOD;
         $this->assertEquals('test-id', $this->activeField->labelOptions['for']);
     }
 
-    public function testWidgetOptions()
+    public function testWidgetOptions(): void
     {
         $this->activeField->form->validationStateOn = ActiveForm::VALIDATION_STATE_ON_INPUT;
         $this->activeField->model->addError('attributeName', 'error');
@@ -643,7 +646,7 @@ EOD;
      *
      * @see https://github.com/yiisoft/yii2/issues/14773
      */
-    public function testOptionsClass()
+    public function testOptionsClass(): void
     {
         $this->activeField->options = ['class' => 'test-wrapper'];
         $expectedValue = <<<'HTML'
@@ -670,7 +673,7 @@ HTML;
         $this->assertEqualsWithoutLE($expectedValue, trim($actualValue));
     }
 
-    public function testInputOptionsTransferToWidget()
+    public function testInputOptionsTransferToWidget(): void
     {
         $widget = $this->activeField->widget(TestMaskedInput::className(), [
             'mask' => '999-999-9999',
@@ -701,7 +704,7 @@ HTML;
         $this->assertStringContainsString('placeholder="pholder_both_direct"', (string) $widget);
     }
 
-    public function testExceptionToString()
+    public function testExceptionToString(): void
     {
         if (PHP_VERSION_ID < 70400) {
             $this->markTestSkipped('This test is for PHP 7.4+ only');
@@ -709,13 +712,13 @@ HTML;
 
         $field = new TestActiveFieldWithException();
 
-        $this->expectException(\Exception::class);
+        $this->expectException(Exception::class);
         $this->expectExceptionMessage('Test exception in toString.');
 
         (string) $field;
     }
 
-    public function testExceptionToStringLegacy()
+    public function testExceptionToStringLegacy(): void
     {
         if (PHP_VERSION_ID >= 70400) {
             $this->markTestSkipped('This test is for PHP < 7.4 only');
@@ -786,7 +789,7 @@ class ActiveFieldExtend extends ActiveField
         $this->getClientOptionsEmpty = $getClientOptionsEmpty;
     }
 
-    public function setClientOptionsEmpty($value)
+    public function setClientOptionsEmpty($value): void
     {
         $this->getClientOptionsEmpty = (bool) $value;
     }
@@ -801,14 +804,14 @@ class ActiveFieldExtend extends ActiveField
     }
 }
 
-class TestValidator extends \yii\validators\Validator
+class TestValidator extends Validator
 {
     public function clientValidateAttribute($object, $attribute, $view)
     {
         return 'return true;';
     }
 
-    public function setWhenClient($js)
+    public function setWhenClient($js): void
     {
         $this->whenClient = $js;
     }
@@ -821,7 +824,7 @@ class TestInputWidget extends InputWidget
      */
     public static $lastInstance;
 
-    public function init()
+    public function init(): void
     {
         parent::init();
         self::$lastInstance = $this;
@@ -840,7 +843,7 @@ class TestMaskedInput extends MaskedInput
      */
     public static $lastInstance;
 
-    public function init()
+    public function init(): void
     {
         parent::init();
         self::$lastInstance = $this;
@@ -867,6 +870,6 @@ class TestActiveFieldWithException extends ActiveField
 {
     public function render($content = null)
     {
-        throw new \Exception('Test exception in toString.');
+        throw new Exception('Test exception in toString.');
     }
 }
diff --git a/tests/framework/widgets/ActiveFormTest.php b/tests/framework/widgets/ActiveFormTest.php
index d017f286a3..b5df5feb1d 100644
--- a/tests/framework/widgets/ActiveFormTest.php
+++ b/tests/framework/widgets/ActiveFormTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\widgets;
 
+use yiiunit\TestCase;
 use yii\base\DynamicModel;
 use yii\base\Widget;
 use yii\web\View;
@@ -16,7 +17,7 @@ use yii\widgets\ActiveForm;
 /**
  * @group widgets
  */
-class ActiveFormTest extends \yiiunit\TestCase
+class ActiveFormTest extends TestCase
 {
     protected function setUp(): void
     {
@@ -24,7 +25,7 @@ class ActiveFormTest extends \yiiunit\TestCase
         $this->mockApplication();
     }
 
-    public function testBooleanAttributes()
+    public function testBooleanAttributes(): void
     {
         $o = ['template' => '{input}'];
 
@@ -63,7 +64,7 @@ EOF,
         );
     }
 
-    public function testIssue5356()
+    public function testIssue5356(): void
     {
         $o = ['template' => '{input}'];
 
@@ -89,7 +90,7 @@ EOF,
         );
     }
 
-    public function testOutputBuffering()
+    public function testOutputBuffering(): void
     {
         $obLevel = ob_get_level();
         ob_start();
@@ -119,7 +120,7 @@ HTML,
         );
     }
 
-    public function testRegisterClientScript()
+    public function testRegisterClientScript(): void
     {
         $this->mockWebApplication();
         $_SERVER['REQUEST_URI'] = 'http://example.com/';
@@ -151,7 +152,7 @@ HTML,
     /**
      * @see https://github.com/yiisoft/yii2/issues/15536
      */
-    public function testShouldTriggerInitEvent()
+    public function testShouldTriggerInitEvent(): void
     {
         $initTriggered = false;
         ob_start();
@@ -173,7 +174,7 @@ HTML,
      * @see https://github.com/yiisoft/yii2/issues/15476
      * @see https://github.com/yiisoft/yii2/issues/16892
      */
-    public function testValidationStateOnInput()
+    public function testValidationStateOnInput(): void
     {
         $model = new DynamicModel(['name']);
         $model->addError('name', 'I have an error!');
diff --git a/tests/framework/widgets/BlockTest.php b/tests/framework/widgets/BlockTest.php
index 50ed5fceb7..ffc65f5c96 100644
--- a/tests/framework/widgets/BlockTest.php
+++ b/tests/framework/widgets/BlockTest.php
@@ -8,12 +8,13 @@
 
 namespace yiiunit\framework\widgets;
 
+use yiiunit\TestCase;
 use yii\widgets\Block;
 
 /**
  * @group widgets
  */
-class BlockTest extends \yiiunit\TestCase
+class BlockTest extends TestCase
 {
     protected function setUp(): void
     {
@@ -25,7 +26,7 @@ class BlockTest extends \yiiunit\TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/15536
      */
-    public function testShouldTriggerInitEvent()
+    public function testShouldTriggerInitEvent(): void
     {
         $initTriggered = false;
 
diff --git a/tests/framework/widgets/BreadcrumbsTest.php b/tests/framework/widgets/BreadcrumbsTest.php
index 6651600a2e..e898da02f2 100644
--- a/tests/framework/widgets/BreadcrumbsTest.php
+++ b/tests/framework/widgets/BreadcrumbsTest.php
@@ -8,6 +8,8 @@
 
 namespace yiiunit\framework\widgets;
 
+use yiiunit\TestCase;
+use ReflectionMethod;
 use yii\widgets\Breadcrumbs;
 
 /**
@@ -15,7 +17,7 @@ use yii\widgets\Breadcrumbs;
  *
  * @group widgets
  */
-class BreadcrumbsTest extends \yiiunit\TestCase
+class BreadcrumbsTest extends TestCase
 {
     private $breadcrumbs;
 
@@ -30,7 +32,7 @@ class BreadcrumbsTest extends \yiiunit\TestCase
         $this->breadcrumbs = new Breadcrumbs();
     }
 
-    public function testHomeLinkNull()
+    public function testHomeLinkNull(): void
     {
         $this->breadcrumbs->homeLink = null;
         $this->breadcrumbs->links = ['label' => 'My Home Page', 'url' => 'http://my.example.com/yii2/link/page'];
@@ -48,12 +50,12 @@ class BreadcrumbsTest extends \yiiunit\TestCase
         $this->assertEquals($expectedHtml, $actualHtml);
     }
 
-    public function testEmptyLinks()
+    public function testEmptyLinks(): void
     {
         $this->assertNull($this->breadcrumbs->run());
     }
 
-    public function testHomeLinkFalse()
+    public function testHomeLinkFalse(): void
     {
         $this->breadcrumbs->homeLink = false;
         $this->breadcrumbs->links = ['label' => 'My Home Page', 'url' => 'http://my.example.com/yii2/link/page'];
@@ -70,7 +72,7 @@ class BreadcrumbsTest extends \yiiunit\TestCase
         $this->assertEquals($expectedHtml, $actualHtml);
     }
 
-    public function testHomeLink()
+    public function testHomeLink(): void
     {
         $this->breadcrumbs->homeLink = ['label' => 'home-link'];
         $this->breadcrumbs->links = ['label' => 'My Home Page', 'url' => 'http://my.example.com/yii2/link/page'];
@@ -88,7 +90,7 @@ class BreadcrumbsTest extends \yiiunit\TestCase
         $this->assertEquals($expectedHtml, $actualHtml);
     }
 
-    public function testRenderItemException()
+    public function testRenderItemException(): void
     {
         $link = ['url' => 'http://localhost/yii2'];
         $method = $this->reflectMethod();
@@ -96,7 +98,7 @@ class BreadcrumbsTest extends \yiiunit\TestCase
         $method->invoke($this->breadcrumbs, $link, $this->breadcrumbs->itemTemplate);
     }
 
-    public function testRenderItemLabelOnly()
+    public function testRenderItemLabelOnly(): void
     {
         $link = ['label' => 'My-<br>Test-Label'];
         $method = $this->reflectMethod();
@@ -111,7 +113,7 @@ class BreadcrumbsTest extends \yiiunit\TestCase
         $this->assertEquals("<li>My-<br>Test-Label</li>\n", $unencodedValue);
     }
 
-    public function testEncodeOverride()
+    public function testEncodeOverride(): void
     {
         $link = ['label' => 'My-<br>Test-Label', 'encode' => false];
         $method = $this->reflectMethod();
@@ -126,7 +128,7 @@ class BreadcrumbsTest extends \yiiunit\TestCase
         $this->assertEquals("<li>My-<br>Test-Label</li>\n", $unencodedValue);
     }
 
-    public function testRenderItemWithLabelAndUrl()
+    public function testRenderItemWithLabelAndUrl(): void
     {
         $link = ['label' => 'My-<br>Test-Label', 'url' => 'http://localhost/yii2'];
         $method = $this->reflectMethod();
@@ -140,7 +142,7 @@ class BreadcrumbsTest extends \yiiunit\TestCase
         $this->assertEquals("<li><a href=\"http://localhost/yii2\">My-<br>Test-Label</a></li>\n", $unencodedValue);
     }
 
-    public function testRenderItemTemplate()
+    public function testRenderItemTemplate(): void
     {
         $link = ['label' => 'My-<br>Test-Label', 'url' => 'http://localhost/yii2', 'template' => "<td>{link}</td>\n"];
         $method = $this->reflectMethod();
@@ -154,7 +156,7 @@ class BreadcrumbsTest extends \yiiunit\TestCase
         $this->assertEquals("<td><a href=\"http://localhost/yii2\">My-<br>Test-Label</a></td>\n", $unencodedValue);
     }
 
-    public function testExtraOptions()
+    public function testExtraOptions(): void
     {
         $link = [
             'label' => 'demo',
@@ -166,7 +168,7 @@ class BreadcrumbsTest extends \yiiunit\TestCase
         $this->assertEquals('<li><a class="external" href="http://example.com">demo</a></li>' . "\n", $result);
     }
 
-    public function testTag()
+    public function testTag(): void
     {
         $this->breadcrumbs->homeLink = ['label' => 'home-link'];
         $this->breadcrumbs->links = ['label' => 'My Home Page', 'url' => 'http://my.example.com/yii2/link/page'];
@@ -193,7 +195,7 @@ class BreadcrumbsTest extends \yiiunit\TestCase
      */
     protected function reflectMethod($class = '\yii\widgets\Breadcrumbs', $method = 'renderItem')
     {
-        $value = new \ReflectionMethod($class, $method);
+        $value = new ReflectionMethod($class, $method);
 
         // @link https://wiki.php.net/rfc/deprecations_php_8_5#deprecate_reflectionsetaccessible
         // @link https://wiki.php.net/rfc/make-reflection-setaccessible-no-op
diff --git a/tests/framework/widgets/ContentDecoratorTest.php b/tests/framework/widgets/ContentDecoratorTest.php
index 5af53edcbc..7ccb68da29 100644
--- a/tests/framework/widgets/ContentDecoratorTest.php
+++ b/tests/framework/widgets/ContentDecoratorTest.php
@@ -8,12 +8,13 @@
 
 namespace yiiunit\framework\widgets;
 
+use yiiunit\TestCase;
 use yii\widgets\ContentDecorator;
 
 /**
  * @group widgets
  */
-class ContentDecoratorTest extends \yiiunit\TestCase
+class ContentDecoratorTest extends TestCase
 {
     protected function setUp(): void
     {
@@ -25,7 +26,7 @@ class ContentDecoratorTest extends \yiiunit\TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/15536
      */
-    public function testShouldTriggerInitEvent()
+    public function testShouldTriggerInitEvent(): void
     {
         $initTriggered = false;
 
diff --git a/tests/framework/widgets/DetailViewTest.php b/tests/framework/widgets/DetailViewTest.php
index beb11d3c84..1ecc72376c 100644
--- a/tests/framework/widgets/DetailViewTest.php
+++ b/tests/framework/widgets/DetailViewTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\widgets;
 
+use yiiunit\TestCase;
 use yii\base\Arrayable;
 use yii\base\ArrayableTrait;
 use yii\base\Model;
@@ -16,7 +17,7 @@ use yii\widgets\DetailView;
 /**
  * @group widgets
  */
-class DetailViewTest extends \yiiunit\TestCase
+class DetailViewTest extends TestCase
 {
     /** @var DetailView */
     public $detailView;
@@ -28,7 +29,7 @@ class DetailViewTest extends \yiiunit\TestCase
         $this->mockWebApplication();
     }
 
-    public function testAttributeValue()
+    public function testAttributeValue(): void
     {
         $model = new ModelMock();
         $model->id = 'id';
@@ -70,7 +71,7 @@ class DetailViewTest extends \yiiunit\TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/13243
      */
-    public function testUnicodeAttributeNames()
+    public function testUnicodeAttributeNames(): void
     {
         $model = new UnicodeAttributesModelMock();
         $model->ИдентификаторТовара = 'A00001';
@@ -95,7 +96,7 @@ class DetailViewTest extends \yiiunit\TestCase
         );
     }
 
-    public function testAttributeVisible()
+    public function testAttributeVisible(): void
     {
         $model = new ModelMock();
         $model->id = 'id';
@@ -172,7 +173,7 @@ class DetailViewTest extends \yiiunit\TestCase
         $this->assertEquals(5, $model->getDisplayedIdCallCount());
     }
 
-    public function testRelationAttribute()
+    public function testRelationAttribute(): void
     {
         $model = new ModelMock();
         $model->id = 'model';
@@ -207,7 +208,7 @@ class DetailViewTest extends \yiiunit\TestCase
         $this->assertEquals('Related Id:<span class="not-set">(not set)</span>', $this->detailView->renderAttribute($this->detailView->attributes[1], 1));
     }
 
-    public function testArrayableModel()
+    public function testArrayableModel(): void
     {
         $expectedValue = [
             [
@@ -235,7 +236,7 @@ class DetailViewTest extends \yiiunit\TestCase
         $this->assertEquals($expectedValue, $this->detailView->attributes);
     }
 
-    public function testObjectModel()
+    public function testObjectModel(): void
     {
         $expectedValue = [
             [
@@ -263,7 +264,7 @@ class DetailViewTest extends \yiiunit\TestCase
         $this->assertEquals($expectedValue, $this->detailView->attributes);
     }
 
-    public function testArrayModel()
+    public function testArrayModel(): void
     {
         $expectedValue = [
             [
@@ -292,7 +293,7 @@ class DetailViewTest extends \yiiunit\TestCase
         $this->assertEquals($expectedValue, $this->detailView->attributes);
     }
 
-    public function testOptionsTags()
+    public function testOptionsTags(): void
     {
         $expectedValue = '<tr><th tooltip="Tooltip">Text</th><td class="bg-red">I`m an array</td></tr>';
 
@@ -319,7 +320,7 @@ class DetailViewTest extends \yiiunit\TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/15536
      */
-    public function testShouldTriggerInitEvent()
+    public function testShouldTriggerInitEvent(): void
     {
         $initTriggered = false;
         $model = new ModelMock();
@@ -365,7 +366,7 @@ class ModelMock extends Model
         return $this->_related;
     }
 
-    public function setRelated($related)
+    public function setRelated($related): void
     {
         $this->_related = $related;
     }
diff --git a/tests/framework/widgets/FragmentCacheTest.php b/tests/framework/widgets/FragmentCacheTest.php
index db099d43db..b81ee21c43 100644
--- a/tests/framework/widgets/FragmentCacheTest.php
+++ b/tests/framework/widgets/FragmentCacheTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\widgets;
 
+use yiiunit\TestCase;
 use Yii;
 use yii\base\View;
 use yii\caching\ArrayCache;
@@ -16,7 +17,7 @@ use yii\caching\ArrayCache;
  * @group widgets
  * @group caching
  */
-class FragmentCacheTest extends \yiiunit\TestCase
+class FragmentCacheTest extends TestCase
 {
     protected function setUp(): void
     {
@@ -27,7 +28,7 @@ class FragmentCacheTest extends \yiiunit\TestCase
         ]);
     }
 
-    public function testCacheEnabled()
+    public function testCacheEnabled(): void
     {
         $expectedLevel = ob_get_level();
         ob_start();
@@ -47,7 +48,7 @@ class FragmentCacheTest extends \yiiunit\TestCase
         $this->assertEquals($expectedLevel, ob_get_level(), 'Output buffer not closed correctly.');
     }
 
-    public function testCacheDisabled1()
+    public function testCacheDisabled1(): void
     {
         $expectedLevel = ob_get_level();
         ob_start();
@@ -69,7 +70,7 @@ class FragmentCacheTest extends \yiiunit\TestCase
         $this->assertEquals($expectedLevel, ob_get_level(), 'Output buffer not closed correctly.');
     }
 
-    public function testCacheDisabled2()
+    public function testCacheDisabled2(): void
     {
         $expectedLevel = ob_get_level();
         ob_start();
@@ -91,7 +92,7 @@ class FragmentCacheTest extends \yiiunit\TestCase
         $this->assertEquals($expectedLevel, ob_get_level(), 'Output buffer not closed correctly.');
     }
 
-    public function testSingleDynamicFragment()
+    public function testSingleDynamicFragment(): void
     {
         Yii::$app->params['counter'] = 0;
 
@@ -122,7 +123,7 @@ class FragmentCacheTest extends \yiiunit\TestCase
         }
     }
 
-    public function testMultipleDynamicFragments()
+    public function testMultipleDynamicFragments(): void
     {
         Yii::$app->params['counter'] = 0;
 
@@ -155,7 +156,7 @@ class FragmentCacheTest extends \yiiunit\TestCase
         }
     }
 
-    public function testNestedDynamicFragments()
+    public function testNestedDynamicFragments(): void
     {
         Yii::$app->params['counter'] = 0;
 
@@ -195,7 +196,7 @@ class FragmentCacheTest extends \yiiunit\TestCase
         }
     }
 
-    public function testVariations()
+    public function testVariations(): void
     {
         $this->setOutputCallback(function ($output) {
             return null;
diff --git a/tests/framework/widgets/LinkPagerTest.php b/tests/framework/widgets/LinkPagerTest.php
index 43efb8c39c..98f010c30e 100644
--- a/tests/framework/widgets/LinkPagerTest.php
+++ b/tests/framework/widgets/LinkPagerTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\widgets;
 
+use yiiunit\TestCase;
 use yii\data\Pagination;
 use yii\helpers\StringHelper;
 use yii\widgets\LinkPager;
@@ -15,7 +16,7 @@ use yii\widgets\LinkPager;
 /**
  * @group widgets
  */
-class LinkPagerTest extends \yiiunit\TestCase
+class LinkPagerTest extends TestCase
 {
     protected function setUp(): void
     {
@@ -44,7 +45,7 @@ class LinkPagerTest extends \yiiunit\TestCase
         return $pagination;
     }
 
-    public function testFirstLastPageLabels()
+    public function testFirstLastPageLabels(): void
     {
         $pagination = $this->getPagination(5);
         $output = LinkPager::widget([
@@ -87,7 +88,7 @@ class LinkPagerTest extends \yiiunit\TestCase
         $this->assertStringNotContainsString('<li class="last">', $output);
     }
 
-    public function testDisabledPageElementOptions()
+    public function testDisabledPageElementOptions(): void
     {
         $output = LinkPager::widget([
             'pagination' => $this->getPagination(0),
@@ -97,7 +98,7 @@ class LinkPagerTest extends \yiiunit\TestCase
         $this->assertStringContainsString('<span class="foo-bar">&laquo;</span>', $output);
     }
 
-    public function testDisabledPageElementOptionsWithTagOption()
+    public function testDisabledPageElementOptionsWithTagOption(): void
     {
         $output = LinkPager::widget([
             'pagination' => $this->getPagination(0),
@@ -107,7 +108,7 @@ class LinkPagerTest extends \yiiunit\TestCase
         $this->assertStringContainsString('<div class="foo-bar">&laquo;</div>', $output);
     }
 
-    public function testDisableCurrentPageButton()
+    public function testDisableCurrentPageButton(): void
     {
         $pagination = $this->getPagination(5);
         $output = LinkPager::widget([
@@ -128,7 +129,7 @@ class LinkPagerTest extends \yiiunit\TestCase
         $this->assertStringContainsString('<li class="active disabled"><span>6</span></li>', $output);
     }
 
-    public function testOptionsWithTagOption()
+    public function testOptionsWithTagOption(): void
     {
         $output = LinkPager::widget([
             'pagination' => $this->getPagination(5),
@@ -141,7 +142,7 @@ class LinkPagerTest extends \yiiunit\TestCase
         $this->assertTrue(StringHelper::endsWith($output, '</div>'));
     }
 
-    public function testLinkWrapOptions()
+    public function testLinkWrapOptions(): void
     {
         $output = LinkPager::widget([
             'pagination' => $this->getPagination(1),
@@ -161,7 +162,7 @@ class LinkPagerTest extends \yiiunit\TestCase
         );
     }
 
-    public function testWithTwoButtons()
+    public function testWithTwoButtons(): void
     {
         $output = LinkPager::widget([
             'pagination' => $this->getPagination(0),
@@ -194,7 +195,7 @@ class LinkPagerTest extends \yiiunit\TestCase
         );
     }
 
-    public function testWithOneButton()
+    public function testWithOneButton(): void
     {
         $output = LinkPager::widget([
             'pagination' => $this->getPagination(0),
@@ -225,7 +226,7 @@ class LinkPagerTest extends \yiiunit\TestCase
         );
     }
 
-    public function testWithNoButtons()
+    public function testWithNoButtons(): void
     {
         $output = LinkPager::widget([
             'pagination' => $this->getPagination(0),
@@ -257,7 +258,7 @@ class LinkPagerTest extends \yiiunit\TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/15536
      */
-    public function testShouldTriggerInitEvent()
+    public function testShouldTriggerInitEvent(): void
     {
         $initTriggered = false;
         $output = LinkPager::widget([
diff --git a/tests/framework/widgets/LinkSorterTest.php b/tests/framework/widgets/LinkSorterTest.php
index 28da0170be..8f0718ebc8 100644
--- a/tests/framework/widgets/LinkSorterTest.php
+++ b/tests/framework/widgets/LinkSorterTest.php
@@ -30,7 +30,7 @@ class LinkSorterTest extends DatabaseTestCase
         $this->mockWebApplication();
     }
 
-    public function testLabelsSimple()
+    public function testLabelsSimple(): void
     {
         $dataProvider = new ActiveDataProvider([
             'query' => Order::find(),
@@ -58,7 +58,7 @@ class LinkSorterTest extends DatabaseTestCase
         ));
     }
 
-    public function testLabelsExplicit()
+    public function testLabelsExplicit(): void
     {
         $dataProvider = new ActiveDataProvider([
             'query' => Order::find(),
@@ -90,7 +90,7 @@ class LinkSorterTest extends DatabaseTestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/15536
      */
-    public function testShouldTriggerInitEvent()
+    public function testShouldTriggerInitEvent(): void
     {
         $initTriggered = false;
         new LinkSorter(
diff --git a/tests/framework/widgets/ListViewTest.php b/tests/framework/widgets/ListViewTest.php
index a00caede36..fc057f0295 100644
--- a/tests/framework/widgets/ListViewTest.php
+++ b/tests/framework/widgets/ListViewTest.php
@@ -8,6 +8,7 @@
 
 namespace yiiunit\framework\widgets;
 
+use Yii;
 use yii\web\Request;
 use yii\data\ArrayDataProvider;
 use yii\data\DataProviderInterface;
@@ -25,7 +26,7 @@ class ListViewTest extends TestCase
         $this->mockApplication();
     }
 
-    public function testEmptyListShown()
+    public function testEmptyListShown(): void
     {
         ob_start();
         $this->getListView([
@@ -37,7 +38,7 @@ class ListViewTest extends TestCase
         $this->assertEqualsWithoutLE('<div id="w0" class="list-view"><div class="empty">Nothing at all</div></div>', $out);
     }
 
-    public function testEmpty()
+    public function testEmpty(): void
     {
         ob_start();
         $this->getListView([
@@ -49,7 +50,7 @@ class ListViewTest extends TestCase
         $this->assertEqualsWithoutLE('<div id="w0" class="list-view"></div>', $out);
     }
 
-    public function testEmptyListNotShown()
+    public function testEmptyListNotShown(): void
     {
         ob_start();
         $this->getListView([
@@ -94,7 +95,7 @@ HTML,
         ], $additionalConfig));
     }
 
-    public function testSimplyListView()
+    public function testSimplyListView(): void
     {
         ob_start();
         $this->getListView()->run();
@@ -112,7 +113,7 @@ HTML,
         );
     }
 
-    public function testWidgetOptions()
+    public function testWidgetOptions(): void
     {
         ob_start();
         $this->getListView(['options' => ['class' => 'test-passed'], 'separator' => ''])->run();
@@ -165,7 +166,7 @@ HTML,
      * @param mixed $itemView
      * @param string $expected
      */
-    public function testItemViewOptions($itemView, $expected)
+    public function testItemViewOptions($itemView, $expected): void
     {
         ob_start();
         $this->getListView(['itemView' => $itemView])->run();
@@ -211,7 +212,7 @@ HTML,
      * @param mixed $itemOptions
      * @param string $expected
      */
-    public function testItemOptions($itemOptions, $expected)
+    public function testItemOptions($itemOptions, $expected): void
     {
         ob_start();
         $this->getListView(['itemOptions' => $itemOptions])->run();
@@ -220,7 +221,7 @@ HTML,
         $this->assertEqualsWithoutLE($expected, $out);
     }
 
-    public function testBeforeAndAfterItem()
+    public function testBeforeAndAfterItem(): void
     {
         $before = function ($model, $key, $index, $widget) {
             $widget = get_class($widget);
@@ -261,7 +262,7 @@ HTML,
     /**
      * @see https://github.com/yiisoft/yii2/pull/14596
      */
-    public function testShouldTriggerInitEvent()
+    public function testShouldTriggerInitEvent(): void
     {
         $initTriggered = false;
         $this->getListView([
@@ -273,7 +274,7 @@ HTML,
         $this->assertTrue($initTriggered);
     }
 
-    public function testNoDataProvider()
+    public function testNoDataProvider(): void
     {
         $this->expectException('yii\base\InvalidConfigException');
         $this->expectExceptionMessage('The "dataProvider" property must be set.');
@@ -291,7 +292,7 @@ HTML,
     /**
      * @dataProvider providerForNoSorter
      */
-    public function testRenderNoSorter($additionalConfig)
+    public function testRenderNoSorter($additionalConfig): void
     {
         $config = array_merge(['layout' => '{sorter}'], $additionalConfig);
 
@@ -302,7 +303,7 @@ HTML,
         $this->assertEqualsWithoutLE('<div id="w0" class="list-view"></div>', $out);
     }
 
-    public function testRenderSorterOnlyWithNoItems()
+    public function testRenderSorterOnlyWithNoItems(): void
     {
         // by default sorter is skipped when there are no items during run()
         $out = (new ListView([
@@ -313,9 +314,9 @@ HTML,
         $this->assertEquals('', $out);
     }
 
-    public function testRenderSorter()
+    public function testRenderSorter(): void
     {
-        \Yii::$app->set('request', new Request(['scriptUrl' => '/']));
+        Yii::$app->set('request', new Request(['scriptUrl' => '/']));
 
         ob_start();
         $this->getListView([
@@ -334,7 +335,7 @@ HTML,
 </ul></div>', $out);
     }
 
-    public function testRenderSummaryWhenPaginationIsFalseAndSummaryIsNull()
+    public function testRenderSummaryWhenPaginationIsFalseAndSummaryIsNull(): void
     {
         ob_start();
         $this->getListView(['dataProvider' => $this->getDataProvider(['pagination' => false])])->run();
@@ -366,7 +367,7 @@ HTML,
     /**
      * @dataProvider providerForSummary
      */
-    public function testRenderSummaryWhenSummaryIsCustom($summary, $result)
+    public function testRenderSummaryWhenSummaryIsCustom($summary, $result): void
     {
         ob_start();
         $this->getListView(['summary' => $summary])->run();
diff --git a/tests/framework/widgets/MenuTest.php b/tests/framework/widgets/MenuTest.php
index b59a1773b7..18a66b208e 100644
--- a/tests/framework/widgets/MenuTest.php
+++ b/tests/framework/widgets/MenuTest.php
@@ -8,12 +8,13 @@
 
 namespace yiiunit\framework\widgets;
 
+use yiiunit\TestCase;
 use yii\widgets\Menu;
 
 /**
  * @group widgets
  */
-class MenuTest extends \yiiunit\TestCase
+class MenuTest extends TestCase
 {
     protected function setUp(): void
     {
@@ -28,7 +29,7 @@ class MenuTest extends \yiiunit\TestCase
         ]);
     }
 
-    public function testEncodeLabel()
+    public function testEncodeLabel(): void
     {
         $output = Menu::widget([
             'route' => 'test/test',
@@ -82,7 +83,7 @@ HTML;
     /**
      * @see https://github.com/yiisoft/yii2/issues/8064
      */
-    public function testTagOption()
+    public function testTagOption(): void
     {
         $output = Menu::widget([
             'route' => 'test/test',
@@ -139,7 +140,7 @@ HTML;
         $this->assertEqualsWithoutLE($expected, $output);
     }
 
-    public function testItemTemplate()
+    public function testItemTemplate(): void
     {
         $output = Menu::widget([
             'route' => 'test/test',
@@ -171,7 +172,7 @@ HTML;
         $this->assertEqualsWithoutLE($expected, $output);
     }
 
-    public function testActiveItemClosure()
+    public function testActiveItemClosure(): void
     {
         $output = Menu::widget([
             'route' => 'test/test',
@@ -208,7 +209,7 @@ HTML;
         $this->assertEqualsWithoutLE($expected, $output);
     }
 
-    public function testActiveItemClosureWithLogic()
+    public function testActiveItemClosureWithLogic(): void
     {
         $output = Menu::widget([
             'route' => 'test/logic',
@@ -240,7 +241,7 @@ HTML;
         $this->assertEqualsWithoutLE($expected, $output);
     }
 
-    public function testActiveItemClosureWithLogicParent()
+    public function testActiveItemClosureWithLogicParent(): void
     {
         $output = Menu::widget([
             'route' => 'test/logic',
@@ -294,7 +295,7 @@ HTML;
         $this->assertEqualsWithoutLE($expected, $output);
     }
 
-    public function testActiveItemClosureParentAnotherItem()
+    public function testActiveItemClosureParentAnotherItem(): void
     {
         /** @see https://github.com/yiisoft/yii2/issues/19060 */
         $output = Menu::widget([
@@ -351,7 +352,7 @@ HTML;
         $this->assertEqualsWithoutLE($expected, $output);
     }
 
-    public function testItemClassAsArray()
+    public function testItemClassAsArray(): void
     {
         $output = Menu::widget([
             'route' => 'test/test',
@@ -406,7 +407,7 @@ HTML;
         $this->assertEqualsWithoutLE($expected, $output);
     }
 
-    public function testItemClassAsString()
+    public function testItemClassAsString(): void
     {
         $output = Menu::widget([
             'route' => 'test/test',
@@ -452,7 +453,7 @@ HTML;
         $this->assertEqualsWithoutLE($expected, $output);
     }
 
-    public function testIsItemActive()
+    public function testIsItemActive(): void
     {
         $output = Menu::widget([
             'route' => 'test/item2',
diff --git a/tests/framework/widgets/PjaxTest.php b/tests/framework/widgets/PjaxTest.php
index adab82eee9..a1e303c7af 100644
--- a/tests/framework/widgets/PjaxTest.php
+++ b/tests/framework/widgets/PjaxTest.php
@@ -15,7 +15,7 @@ use yiiunit\TestCase;
 
 class PjaxTest extends TestCase
 {
-    public function testGeneratedIdByPjaxWidget()
+    public function testGeneratedIdByPjaxWidget(): void
     {
         ListView::$counter = 0;
         Pjax::$counter = 0;
@@ -43,7 +43,7 @@ class PjaxTest extends TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/15536
      */
-    public function testShouldTriggerInitEvent()
+    public function testShouldTriggerInitEvent(): void
     {
         $initTriggered = false;
         ob_start();
diff --git a/tests/framework/widgets/SpacelessTest.php b/tests/framework/widgets/SpacelessTest.php
index f4c40f0ad9..0483db5265 100644
--- a/tests/framework/widgets/SpacelessTest.php
+++ b/tests/framework/widgets/SpacelessTest.php
@@ -8,14 +8,15 @@
 
 namespace yiiunit\framework\widgets;
 
+use yiiunit\TestCase;
 use yii\widgets\Spaceless;
 
 /**
  * @group widgets
  */
-class SpacelessTest extends \yiiunit\TestCase
+class SpacelessTest extends TestCase
 {
-    public function testWidget()
+    public function testWidget(): void
     {
         ob_start();
         ob_implicit_flush(false);
@@ -48,7 +49,7 @@ class SpacelessTest extends \yiiunit\TestCase
     /**
      * @see https://github.com/yiisoft/yii2/issues/15536
      */
-    public function testShouldTriggerInitEvent()
+    public function testShouldTriggerInitEvent(): void
     {
         $initTriggered = false;
         $spaceless = Spaceless::begin(