Fatal error: Uncaught Error: Class "Drupal\KernelTests\Core\Entity\EntityKernelTestBase" not found in /home/www/drupal8/test/core/modules/field/tests/src/Kernel/EntityReference/EntityReferenceFormatterTest.php:23 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/field/tests/src/Kernel/EntityReference/EntityReferenceFormatterTest.php on line 23