Aircraft engineering staff have had random blood/alcohol testing for a few years now. In my field (North Sea helicopters) this was mostly brought into force in response to customers (oil companies) demands.
The testing is very expensive and not carried out that often. We have had positive tests on about 2 guys to my knowledge, but the thought of the test may be enough to have the desired effect on the behaviour of the workforce.
One area of concern is the myriad of chemicals that engineers come into contact with. The testers insist on a full detailed list of possible contaminants of a subjects' system, some of which can be introduced by contact. These lists can be very long.