Fatal error: Uncaught Error: Class "Drupal\KernelTests\Core\Entity\EntityKernelTestBase" not found in /home/www/drupal8/test/core/tests/Drupal/KernelTests/Core/Field/FieldItemTest.php:16 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/tests/Drupal/KernelTests/Core/Field/FieldItemTest.php on line 16