I don't see the problem in this. In my old school plenty underage kids were smokers and drug abusers/drinkers. You'll have nothing to fear from these tests. Such tests are necessary in Adult life at times depending on where you work.
If a kid can't go on a school trip because he was found to be smoking weed, then that's the kid's problem for smoking it on a School day.
If a kid can't go on a school trip because he was found to be smoking weed, then that's the kid's problem for smoking it on a School day.