Watching the video provided in the lesson plan for the What's for Lunch? app provided my students with a basis for the interactions that may/should take place during prototype testing. Debriefing the sample video and making sure that they have an understanding of the roles made it a rather "pain free" experience for them and for myself. But of course, they are students and they may come up with unexpected interactions which makes the lesson all the more interesting.
I required them to take a video of the testing and post them in our shared folder so they may see how their classmates did.