Fatal error: Uncaught Error: Class "Drupal\Tests\migrate_drupal\Kernel\d6\MigrateDrupal6TestBase" not found in /home/www/drupal8/test/core/modules/migrate_drupal/tests/src/Kernel/IdMapTableNoDummyTest.php:12 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/migrate_drupal/tests/src/Kernel/IdMapTableNoDummyTest.php on line 12