It's basically the same as a normal driving test but the practical part is longer (1 hour).
So you'll have to do exactly the same theory test that new drivers have to go through and then have an hour long practical test, including a 10 minute period of following road signs (rather than following the directions of the examiner).
The most likely reasons for failing would probably be
(a) excess speed ;
(b) failing to keep a correct distance behind the vehicle ahead, even when waiting to overtake (e,g at least 20 car lengths behind at 50mph); and
(c) failure to check your mirrors often enough (i.e. at least once every 10 seconds and more often in heavy traffic).
And then you've only got to worry about the cost of your insurance . . .