Fatal error: Uncaught Error: Class "Drupal\Tests\migrate\Kernel\MigrateTestBase" not found in /home/www/drupal8/test/core/modules/migrate/tests/src/Kernel/MigrateRollbackTest.php:16 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/migrate/tests/src/Kernel/MigrateRollbackTest.php on line 16