Fatal error: Uncaught Error: Class "Drupal\Tests\migrate_drupal\Kernel\MigrateDrupalTestBase" not found in /home/www/drupal8/test/core/modules/migrate/tests/src/Kernel/Plugin/MigrationProvidersExistTest.php:15 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/migrate/tests/src/Kernel/Plugin/MigrationProvidersExistTest.php on line 15