Test mine every month like clockwork now, @gavin365. I set a calendar reminder because I got paranoid after that one storm. It's not just about the big weather events either, my power flickered last Tuesday from a truck hitting a pole and it kicked right in. You notice the battery life dropping a bit each time, so you know when it's getting weak before it totally fails on you. Way better than the surprise of a dead unit when you actually need it.
Honestly I should be more paranoid like Caleb but... I check mine maybe twice a year. Which means I'm basically hoping it works when my old house finally gets hit with a real outage. My smooth brain just forgets until the lights actually go out.