How much Marijuana would you have to be exposed to in order to have a drug test come up positive?

My daughter and her husband went to a Metallica concert the other night and a few people were smoking pot at the concert. They didn’t stay around it but it brought up the question, “What if her husband were random drug tested tomorrow?
Would being at a concert where you could smell it make it come up positive?
I have not been around it for 35 years, so I know testing must have come a long way since then.