Actually, the dinghy situation is a PAN call rather than a MAYDAY.
Actually, isn't it a MAYDAY RELAY
Anyway, I think it is a waste of time. I think the examiner on the flight test should be able to assess all aspects of your flying skills, including RT, and make a judgement as to whether you are competent to fly and communicate. If not, then maybe some remedial training in an RT simulator and seperate RT test should be required. RT is one of those things you can't learn in 45 hours and be expected to be British Airways correct each time. You learn by doing.......