added unit tests for schema detection

fixed some issues with schema detection

tests/unit/framework/db/pgsql/PostgreSQLQueryTest.php

@@ -0,0 +1,16 @@
+<?php
+
+namespace yiiunit\framework\db\pgsql;
+
+use yii\db\pgsql\Schema;
+use yiiunit\framework\db\QueryTest;
+use yiiunit\framework\db\SchemaTest;
+
+/**
+ * @group db
+ * @group pgsql
+ */
+class PostgreSQLQueryTest extends QueryTest
+{
+    public $driverName = 'pgsql';
+}