How to test internal controllers without route in Symfony 2

I am trying to reduce redundant code by refactoring template and controller code into reusable components, which I then use via the render(controller('AppBundle:Foo/Bar:baz')) construct inside my other templates.

Of course I would like to test these components. In the examples regarding functional testing, however, an actual route is required to make fake test requests. But my BarController here is purely internal and has no routes attached to it. How can I test this controller?

Creating dummy routes is not always possible, because some of the arguments are model objects that cannot be passed via URL. Am I approaching this the wrong way?