Fatal error: Uncaught Error: Class "Drupal\Tests\migrate_drupal\Kernel\d6\MigrateDrupal6TestBase" not found in /home/www/drupal8/test/core/modules/user/tests/src/Kernel/Migrate/d6/MigrateUserTest.php:18
Stack trace:
#0 {main}
thrown in /home/www/drupal8/test/core/modules/user/tests/src/Kernel/Migrate/d6/MigrateUserTest.php on line 18