It could take up to a week for Xanax to completely clear from your system. Yes, it is detectable. If you have a prescription for it the drug testing place should take that into consideration. If you don't have a prescription currently, perhaps you could get one before you pee in the cup.
Xanax [alprazolam] has plasma half life of around 24 hours and remains in blood for more than 1 week in detectable levels, detectable in urine for at least 48 hours.