Not all tests are random, Commanders can request test on certain people based on probable cause or even just based on an incident. How the test is phrased determines what possible outcomes or punishments can be dealt out.

Aye the commander can "Direct" a Urinalysis however, if it is Commander Directed they can't use it against you in a Court Marshall. What kind of sense does that make? I had a troop once and every one knew she was a druggie, however the commander would not direct her conduct a urinalysis because they wouldn't be able to use it against her, They finally got her because of the "things" that follow drug use, Poor performance at work, showing up late all the time, not paying her bills, and then she went AWOL, well when they finally got her back to base she was restricted to base, and had to be escorted when outside of her dorm room, She finally got busted for drugs when she did a line in her escorts vehicle while he was driving. It still made no sense to me that the commander couldn't bust her for drugs months earlier when we all knew she was doing it.