This is a good test because it uses a pair of signals with exactly the same frequency harmonic content but having different phase. It prevents the listener from obtaining frequency cues that expose a difference in phase. Cancellations of certain frequencies, beat frequencies and things that make response aberrations are pretty easy to detect, but absolute phase isn't. So you're going to have a very hard time finding people that can detect a sawtooth from a reverse sawtooth in a blind test. Try it and see.