In the military, it's a complete surprise. But you should expect it will happen after 4-day weekends (any federal holiday is a 4-day weekend, aka 96 hour pass), block leave, anyone getting hurt, arrested for drugs, etc.

You show up for morning formation, platoon sergeant or other person in authority announces it is a urinalysis and no one can leave the area until everyone takes a piss. Water is brought to the site to increase hydration as necessary. A noncommissionned officer or above must see the urine leaving your body (for females, there's a flashlight and a mirror).

Good times are had by all.

In the Reserves and National Guard, you're retarded if you do not expect to piss in a cup on your monthly drill weekend or at annual training. Hunter was in the Reserves.