I agree, drug testing is degrading to the person being tested and to the person testing because they can be faked and are only good for that moment.
My rule was that it is my home, my safety zone and that if I even suspect anyone is using drugs they must leave. The onus is on them to stay clean and behave as a clean person should behave.
I also had a curfew of 11 pm, because MY sleep depended on everyone being home. My son was a grown man and felt he was too old for a curfew...I told him I didn't care, he could follow my rules in my home or live as he likes any place else.
There were more rules, more agreements, but in the end it never worked out, not once. He moved home many times and each time I thought it would be different...it never was.
That is not to say your child won't respect your rules and behave well. I pray your child stays on a good path. My point in saying what I said is to let you know that if this all goes south, it's not your fault, and that it's your home and you can have any rules you like.
Hugs