thats the problem with these things if they rev it up and the valves shoot out ad start dancing on the bonnet they can not be held for it and it's up to the owner of the vehicle to sort out. some of them even make you sign a waver. i don't see the point in revving it up even once.
it's for the diesel smoke test or immisions if you like been in place a few years now we've not really had any go bang just depends on how hard they rev it luckily my mate who does mine is alright lucky me just make shaw you have enough engine oil in it and you should be fine as extreme says we're ok no cam belt