reverted:
--- b/core/modules/system/src/Tests/Migrate/d6/MigrateSystemFilterTest.php
+++ a/core/modules/migrate_drupal/src/Tests/d6/MigrateSystemFilterTest.php
@@ -2,17 +2,15 @@
 
 /**
  * @file
+ * Contains \Drupal\migrate_drupal\Tests\d6\MigrateSystemFilterTest.
- * Contains \Drupal\system\Tests\Migrate\d6\MigrateSystemFilterTest.
  */
 
+namespace Drupal\migrate_drupal\Tests\d6;
-namespace Drupal\system\Tests\Migrate\d6;
-
-use Drupal\migrate_drupal\Tests\d6\MigrateDrupal6TestBase;
 
 /**
  * Upgrade filter variables to system.*.yml.
  *
+ * @group migrate_drupal
- * @group system
  */
 class MigrateSystemFilterTest extends MigrateDrupal6TestBase {
 
only in patch2:
unchanged:
--- a/core/modules/migrate_drupal/src/Plugin/migrate/source/d6/Menu.php
+++ b/core/modules/system/src/Plugin/migrate/source/d6/Menu.php
@@ -2,10 +2,10 @@
 
 /**
  * @file
- * Contains \Drupal\migrate_drupal\Plugin\migrate\source\d6\Menu.
+ * Contains \Drupal\system\Plugin\migrate\source\d6\Menu.
  */
 
-namespace Drupal\migrate_drupal\Plugin\migrate\source\d6;
+namespace Drupal\system\Plugin\migrate\source\d6;
 
 use Drupal\migrate_drupal\Plugin\migrate\source\DrupalSqlBase;
 
only in patch2:
unchanged:
--- a/core/modules/migrate_drupal/src/Tests/d6/MigrateDateFormatTest.php
+++ b/core/modules/system/src/Tests/Migrate/d6/MigrateDateFormatTest.php
@@ -2,18 +2,19 @@
 
 /**
  * @file
- * Contains \Drupal\migrate_drupal\Tests\d6\MigrateDateFormatTest.
+ * Contains \Drupal\system\Tests\Migrate\d6\MigrateDateFormatTest.
  */
 
-namespace Drupal\migrate_drupal\Tests\d6;
+namespace Drupal\system\Tests\Migrate\d6;
 
 use Drupal\migrate\MigrateExecutable;
 use Drupal\Core\Database\Database;
+use Drupal\migrate_drupal\Tests\d6\MigrateDrupal6TestBase;
 
 /**
  * Upgrade date formats to core.date_format.*.yml.
  *
- * @group migrate_drupal
+ * @group system
  */
 class MigrateDateFormatTest extends MigrateDrupal6TestBase {
 
only in patch2:
unchanged:
--- a/core/modules/migrate_drupal/src/Tests/d6/MigrateMenuTest.php
+++ b/core/modules/system/src/Tests/Migrate/d6/MigrateMenuTest.php
@@ -2,19 +2,20 @@
 
 /**
  * @file
- * Contains \Drupal\migrate_drupal\Tests\d6\MigrateMenuTest.
+ * Contains \Drupal\system\Tests\Migrate\d6\MigrateMenuTest.
  */
 
-namespace Drupal\migrate_drupal\Tests\d6;
+namespace Drupal\system\Tests\Migrate\d6;
 
 use Drupal\migrate\MigrateExecutable;
 use Drupal\Core\Database\Database;
+use Drupal\migrate_drupal\Tests\d6\MigrateDrupal6TestBase;
 use Drupal\system\Entity\Menu;
 
 /**
  * Upgrade menus to system.menu.*.yml.
  *
- * @group migrate_drupal
+ * @group system
  */
 class MigrateMenuTest extends MigrateDrupal6TestBase {
 
only in patch2:
unchanged:
--- a/core/modules/migrate_drupal/tests/src/Unit/source/d6/MenuTest.php
+++ b/core/modules/system/tests/src/Unit/Migrate/source/d6/MenuTest.php
@@ -2,23 +2,23 @@
 
 /**
  * @file
- * Contains \Drupal\Tests\migrate_drupal\Unit\source\d6\MenuTest.
+ * Contains \Drupal\Tests\system\Unit\Migrate\source\d6\MenuTest.
  */
 
-namespace Drupal\Tests\migrate_drupal\Unit\source\d6;
+namespace Drupal\Tests\system\Unit\Migrate\source\d6;
 
 use Drupal\Tests\migrate\Unit\MigrateSqlSourceTestCase;
 
 /**
  * Tests D6 menu source plugin.
  *
- * @group migrate_drupal
+ * @group system
  */
 class MenuTest extends MigrateSqlSourceTestCase {
 
   // The plugin system is not working during unit testing so the source plugin
   // class needs to be manually specified.
-  const PLUGIN_CLASS = 'Drupal\migrate_drupal\Plugin\migrate\source\d6\Menu';
+  const PLUGIN_CLASS = 'Drupal\system\Plugin\migrate\source\d6\Menu';
 
   // The fake Migration configuration entity.
   protected $migrationConfiguration = array(