The drug testing regime seems to me to be an enforcement of lifestyle choices.
A test for extant primary substance in a persons body is oral fluid and breathe test.
This tells me if the person has drank alchohol or used drugs in the last 12 - 24 hours.
Urine analysis tells me if the person has used drugs in the previous weeks. Urine tests for metabolites of the substance not the substance its self. Urine test does not show that the person is under the influence at time of the test.