Fixed PHPunit tests

tests/Serializer/StructuralElementNormalizerTest.php

@@ -41,6 +41,9 @@ class StructuralElementNormalizerTest extends WebTestCase
         //Get an service instance.
         self::bootKernel();
         $this->service = self::getContainer()->get(StructuralElementNormalizer::class);
+        //Inject the serializer, as the normalizer as this is not handled by the DI container
+        $this->service->setNormalizer(self::getContainer()->get('serializer'));
+
     }
 
     public function testNormalize(): void