As far as I am aware the reverse lights have to work if fitted. If you don't have any it won't fail but if you do it will. I found this out when I had my old mini as I put 60's lights on the rear which did not have a reverse light built in when the original lamps on the car did. I thought I would have to fit a reverse lamp but the tester said that if the car doesn't have any he can't test them and reverse lights aren't a legal requirement.
Nick