Screw the MOT test, you realise they are a safety feature?
Coupled with the seatbelt, that thing could save your life. It only takes some idiot on the other side of the road to make a bad decision to overtake. Both at 30, you're hit with one hell of a smash.
No it's not part of the MOT, if you're worried, disconnect the light, noone will bother checking.
DO remember what the airbag is designed to do.