They may have you drop a urine test. They are allowed to drop a urine test. You may have a problem especially if they figure out you smoked weed in jail which is a felony.
Seth Weinstein, Esq.
Practicing throughout Southern California
This reply should NOT be considered a legal opinion of your case / inquiry. At this time I do not have sufficient factual/legal documentation to give a complete answer to your question and there may be more to the issues you raised then I have set out in my brief reply.
There's a pretty good chance that they'll test you, but since you've already been out, they wouldn't likely be able to prove that you smoked in jail.
How much did you smoke? How many days have passed? Was it just one time?