It would depend on the charge, the conditions of probation, the probation officer, and the status of that office on the day of the visit. In other words, if you think they might, they probably will. You should act "as if" you could be drug tested at any time: stay clean. But you knew that.
Probation knows how long each drug is likely to show up in a test, so don't worry about failing for pot when you last smoke two weeks ago. Many times, they'll even forgive an unexplained failed first test anyway. But if they do it is your one freebie, so keep it clean.
Agree with Mosca. You should always expect for the worst with probation officers. Assuming this was a DUI case, bringing along with it issues regarding either drugs or alcohol, you should expect a drug test every time you go in. As my colleague above correctly states, cannabis can stay in your system for sometimes up to 25-30 days, so your first visit should not violate you if you drop dirty for THC. The next time your urine should be clear.
I agree with Mr. Mosca. Often, the Judge will ask you at sentencing whether you would be able to pass a drug test if administered today. If you said yes, the judge would note that in your file and even a first failed drug test could be used against you. Otherwise, for the most part, they will drug test you on your first visit, but it is expected that you will not pass and it will not be used against you.
Sign up to receive a 3-part series of useful information and legal advice about DUIs.