if its just a urine test that isnt sent to a lab, which is what they have at my school, just drink lots of water. depending on the environment, they wont even care if its diluted. Most the time, the people testing are just doing their job and dont really care if you pass/fail, in fact, its probably more paperwork if you fail.

Ask people who have been tested at the same place as you what the experience is like, whether they toke or not.

Is it simply a piss test with indicator? just drink a lot of water

Do they watch you, if not, some people put "clean" urine in an unlubricated condom. Kinda weird but whatever

The tests at our school test for a fairly high amount of THC, so if you smoked a few days before and your pee is somewhat hyrdrated youre probably fine

Also, make sure its not your first piss of the day