I noticed in #1935922: Convert PhpStorage tests to phpunit it's doing a lot of this:
/**
* @file
- * Definition of Drupal\system\Tests\PhpStorage\FileStorageTest.
+ * Definition of Drupal\Tests\Component\PhpStorage\FileStorageTest.
*/
-namespace Drupal\system\Tests\PhpStorage;
+namespace Drupal\Tests\Component\PhpStorage;Right now, we're only doing this for PHPUnit tests, but it probably makes sense to do this for all tests.