So let me get this straight - you are not type rated on the aircraft, you have no intention or qualification to fly that aircraft, yet you are to be "prosecuted" for an offence that in fact you cannot commit, albeit lawfully (putting aside the silly idea of hijacking, - they will never get random tested before the event - Religious and Political intoxication doesn't count!).
Is it an offence to wear a uniform and have a drink, without the intention to fly? Does Random testing cover this?
Is it an offence to be positioning out of uniform and have a drink? I would liken it to sitting at home, having someone coming to your home to carry out a random test in the event that you at some time will drive your motor vehicle?
I think that even in fact you are in uniform, on the Gen Deck, but without the authorisation to fly, then you have NO INTENTION to operate. Test away, get a positive result, what is the offence? Particularly after the flight. What have you done wrong? I think any authority would be hard pressed to bring a prosecution, unless of course there is other legislation that provides otherwise - please, if anyone knows, do tell.
There certainly is good reason no doubt to "test" the operating crew and we should all expect that to happen to us at some time in our careers.