Cycle it by hand with full mags a bunch of times (pointed in a safe direction of course), and then confirm with a 2-3 mags of live fire. That's what I've done for years and it has never let me down once.
I make it a point to use any new mags I get on the next trip to the range (the farm really). After that I call it good. I’d say a couple of mags worth would be fine, but why stop there? Shooting is fun! Only time I’ve had problems is when I rapid fire. 33 rd Glock sticks have done it in my Glock but not in my PC carbine for some reason. My 10/22 will do it with the 2x25 mag.