The leak may come from the cavity between the IDG and the gearbox, usually a carbon seal, they can leak staticaly. You are correct, if the approved doccument allows for 3 drops per minute at idle, a run while monitoring by qualified personell would be required. If this is the leak I am thinking of it would be most likely engine oil, not IDG oil. 3 drops is hard to measure, often with similar leaks we would tape a bag to the dripping line to collect the leakage.