I've always thought it a personal preference. Personally, I've always gone with crab method, but that's what I was taught (Rule of Primacy?).
Indeed, it wasn't until moving to the USA that I ever heard of the wing down method - but I see nothing wrong with it for a light aircraft, especially a high wing.
Idle curiosity - what aircraft type are you being taught to land in a 20 knot cross wind (presumably as a student).
As for the "test" - you will be regarded as "Assuming all the responsibilities of the pilot in command", so the decision will be yours alone as to which method you use. It just has to work.