Have you ever been drug screened? There's varying levels of privacy allowed depending on the company doing the screening (including absolutely none) but there's lots of policies in place to where using someone else's urine is very difficult to impossible. Part of my spouse's current job is to watch people pee for drug tests. Also I've heard of at least one company that does hair tests.

If you have enough forewarning to catheterize yourself and fill up with clean urine beforehand it's a non-issue. Obviously this is sensitive to how things are scheduled, but tends to work pretty well when one isn't closely watched between getting notice of the test and getting tested