On my motorhome website there are frequent niggles that when taking the vehicle to the garage for service and MOT the garage did the MOT first and if it was failed the faults corrected, where possible, at the service stage.
They argue that logically the service should be done first so that any faults could be corrected before being recorded as an MOT failure and which would also avoid the need for re-testing.
I didn't know that the reason that the MOT must be done first is so that testing stations' data reflects the actual condition of vehicles when in use on the road.