How to check 4×4 operation on 2004.5 sportsman

So I was out riding around the yard the other day in about 6" of snow and noticed that the rear end would wash out once and a while when I would get on it. I had the AWD on and thought it was strange that it would do that. Now my tires are not the best but I was wondering if there was an easy way to check if the 4×4 is working.

Thanks