Fatal error: Uncaught Error: Class "Drupal\Tests\field\Kernel\FieldKernelTestBase" not found in /home/www/drupal8/test/core/modules/field/tests/src/Kernel/FieldAttachStorageTest.php:14 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/field/tests/src/Kernel/FieldAttachStorageTest.php on line 14