Whether or not someone gets drug tested is not always dependent on the job they do. Some car detailers may get drug tested if the company that they are going to work for requires drug testing. Not all companies do require drug testing.
Whoa! Too many circumstances are given without enough information. If you were injured on the job and were drug tested as a result, and you tested positive, you could be disciplined or dismissed. Questioner will have to supply more info about the "harassment" portion of the question.