Fatal error: Uncaught Error: Class "Drupal\Tests\migrate_drupal\Kernel\d6\MigrateDrupal6TestBase" not found in /home/www/drupal8/test/core/modules/file/tests/src/Kernel/Migrate/d6/MigrateFileTest.php:17 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/file/tests/src/Kernel/Migrate/d6/MigrateFileTest.php on line 17