Good way to test auto is to try and do a burn out on a sloppy/slippery surface, it'll engage front tires and stop you if it's working, whenever I test drive a used truck/SUV I always test the 4x4 by going to an open area, engaging 4 hi give it a second, drive forward, max the steering all the way left or right, once the vehicle enters the tight circle the vehicle should feel like its rocking, that means 4x4 works, if it doesn't it's still in 2 wheel, I do this everytime because I bought a truck a while ago before I learnt that and just pushed the button it flashed and went solid even tho the 4x4 didn't work, ended up fixing it though so it was all good, but that's the way I test 4x4 a mechanic taught me that