Fatal error: Uncaught Error: Class "Drupal\file\Tests\FileFieldTestBase" not found in /home/www/drupal8/test/core/modules/file/src/Tests/FileFieldWidgetTest.php:22 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/file/src/Tests/FileFieldWidgetTest.php on line 22