Unless mistaken, they announce ahead of time what they will test for. Gee, that's easy, don't take what's on the banned substance list and I think it's mostly for certain diuretics. That only happened in the last 6 or 7 years after Momo and Munzer died, Matarazzo had to go to the hospital, and Dillet "froze" on stage.
As for Priest, there are a couple of interviews with him floating around where he is open about his drug use. The problem is that the cycles are laughably light and a lot don't believe him. But I like the attitute: I don't give a shit if people know what I take.
One is on t-mag.com and is called "Dead Man Talking." The other, even better, I can't recall the name of. He states his first cycle was at 19 and if you see pictures of him at 17, dude does have some ridiculous genes. Look them up, they are a good read.