When I have taken urine drug tests for employment, they have had us do every other requirement first (eye exam, paperwork, etc.) and then have us line up for the urine test. At that point, one person goes in the little bathroom alone, the water is turned off from outside of the bathroom, they pee in a cup with a temperature strip, hand it to the person administering the test and then they wash their hands in the hallway.
I’m sure not every company requires such rigorous testing… but my jobs (in biotech and medical settings) have been close to impossible to fake.