getting arguments in controller when calling it from twig template

I'm trying to access variables in my controller that I set in my function calling in twig. It actually looks like this:

{{ render(controller('AppBundle:Domain:show', {
        'test': 'ok'
})) }}

And in my controller it looks like this:

public function showAction(Request $request, $test = null)
{
    $test = $test ? $test : 'notOk';
    var_dump($test); // result "notOK"
    die;
}

My aim is to have var_dump($test); resulting in 'ok'