One toke isn't going to last in your system for a month. If you plan to smoke on a friday night and just that night, you'll be fine monday.

If you indeed do get tested, drink plenty of water so you urinate a few times before taking the test. That way you'll give them a diluted sample. Also only submit the middle-stream of your piss, piss out the beginning which contains the most THC.

Just don't get in the habit again, or you'll really screw yourself.