I can't really see why random testing is needed in a place of business.
First, it seems wasteful. Why pay for drug testing someone you have no reason at all to suspect the employee? It seems to me, employers would be better off only testing those employees who have given management reason to suspect drug use.
Second, why would testing need to be done in the first place? If someone is doing their job poorly fire them, suspend them, whatever. You don't need drug testing to know whether your employee is bad at his job. If someone is doing their job well, then what does it matter that they also may be on drugs? Drug testing, and mostly, random drug testing does not seem to be necessary.