There's an interesting short piece in Focus (a German news magazine) this morning. They've gone and done a piece on airline operations and this idea by the German transport industry.....to audit pilots at random.
After the March 2015 episode with German Wings....where the pilot had physiological problems and taking medication that the airline wasn't aware of......there's this suggestion that they (the ministry) wants the ability to just appear at some airport....hand a urine cup to some pilot and demand a test for alcohol, prescribed medicine and illegal drugs.
Oddly, the pilot's union came out and said this was the worst thing that the government could do, and stopped just short of saying legal proceedings would be forced if they tried to carry out the tests.
If you went out and surveyed the public....most want something done after seeing the problems of the German Wings pilot.
The problem I see is that you will likely discover that airline pilots are taking a fair amount of caffeine-laced drugs to keep themselves alert. If they were mixing some other drug into the mix....there's likely no tests being done by anyone by combining both the unknown drugs and caffeine-based drugs. It'll open the door for a wide discussion over what you are asking the pilots to do a regular basis and their problems in staying focused.
My bet is that the transport ministry will make it happen and then get pushed into court to be challenged if they have the legal authority to test pilots.