When I ran the coffee shop we had a random drug testing policy.  Once the owner asked me if we should test everyone I said "Sure, if you only want you and me to run the place while we hire a new staff."  We didn't test anyone.  LOL
At the dealership we had a piss cup test before employment, and they have a policy for random testing, but they've never done it.  You pretty much know who smokes pot after work.  And again, I don't think they want to have to hire a bunch of new techs and parts guys either.  lol