Does refrigerant need to be remove to test for leaks?

My car's A/C was not getting really cold, it was chilling, but not as good as it could be. So I got an A/C service and was told that the condenser had a leak. Now, this must be very small indeed, as the A/C was working. Upon being told about the price (which I thought was very high - and this hunch proved to be correct) I said just put it back together and I'll think about it. But the mechanic refused to recharge the system, saying it was offence if a leak was present. So now $100.00 later I have a car with no working A/C. "If it ain't broke, don't fix it" comes to mind. So the question is, did the gas need to be taken out to test for leaks?