Fatal error: Uncaught Error: Class "Drupal\Tests\field\Kernel\FieldKernelTestBase" not found in /home/www/drupal8/test/core/modules/image/tests/src/Kernel/ImageItemTest.php:21 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/image/tests/src/Kernel/ImageItemTest.php on line 21