Fatal error: Uncaught Error: Class "Drupal\Tests\media\Kernel\MediaKernelTestBase" not found in /home/www/drupal8/test/core/modules/media/tests/src/Kernel/MediaSourceTest.php:16 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/media/tests/src/Kernel/MediaSourceTest.php on line 16