I agree that `_rawFunction` is kind of an ugly way to go, but as far as I can tell it's the most "direct" way of testing only the helper, while not simultaneously testing part of Ember's rendering stack.  The speed difference between the two approaches is enough that I would think it's useful to include both approaches.  I think that doing the "render template" method first is a good idea, with an explanation/disclaimer on the `_rawFunction` method.