Unless nerding out on them, I mostly just put them through a practice session. If they work, GTG. For more...
A new, standard config OEM mag from a well established model- Nothing specific, if no issues through a practice session it's GTG. Think G19.
Anything else, new model gun, new model mag, modified mag- Verify hold open empty, shoot with 1 round, shoot with 4-5 rounds (where rounds transition from double to single stack or can bridge), shoot with full capacity. Also, using the same capacity intervals, try with cartridges of different OALs and bullet profiles.