Fatal error: Uncaught Error: Class "Drupal\Tests\media\FunctionalJavascript\MediaSourceTestBase" not found in /home/www/drupal8/test/core/modules/media/tests/src/FunctionalJavascript/MediaSourceFileTest.php:13 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/media/tests/src/FunctionalJavascript/MediaSourceFileTest.php on line 13