Yes, I need to use the loader. Otherwise the following exception is being thrown: https://github.com/fabpot/Twig/blob/master/lib/Twig/Loader/Filesystem.php#L191

As a workaround I could try to alter `\Symfony\Bridge\Twig\Tests\Command\LintCommandTest::createCommandTester()` method and pass a filename as an argument. Then I'll be able to set a path only in unit tests.

However it would not help with the `STDIN` case. In this case I could invoke `$loader->getPaths()`, then add a current path, but restore path configuration directly after an invocation.