Personally, I don't know if it's something that should be tested. What I mean, is I think it is something to develop. I know different dogs have better naturaly wind than others and certain lines are known for a more natural ability here than others. However, I believe the ability to breath through a contest can be developed in any dog.

So to answer your question, I say to "test" a dogs aerobic ability, simply put them to work. It's plenty legal to run a catmill, hand walk, bicycle, etc. and you'll get a good understanding of how your dog can breath. Keep at it and your dog will improve that ability.