Testing controller concerns in Rails

Concerns are a great way to organize and de-duplicate code in Rails.One of my favorite use cases is to abstract everything out of the ApplicationController into concerns. This begs the question: how do you test these concerns?The approach for testing concerns is a bit of a judgement call as they're always mixed in with a class and aren't used on their own. Ideally we'd write tests to verify the behavior of a class which would also test the concern in the bargain.