I feel your pain
I have been doing this exact same thing for the last couple of weeks and there is virtually no information available on how to apply unit testing with puremvc.
I've read some posts on this forum about this subject but they're more like suggestions because I think no one still knows how to properly unit test their apps. I too was hoping for a tutorial or best practices guide on this but I think this is still a ways off.
The next best thing is if someone (who has this figured out) could post/share a demo of a real working application with a tight unit testing (preferably flexunit) integration.
After reading the posts on unit testing, trying out somethings to really experience the troubles firsthand, and re-reading these posts, I think I'm finally starting to see the light.
The only problem is, is that I have no idea if what I'm doing is the "correct way" to do it cuz there is nothing to compare it to.
So I suggest that we all think about this problem and post our ideas and findings to sort this thing out once and for all.
Maybe we could even get a best practices guide out of all this
I'll keep you posted on my progress.