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