Functional reliability is dependent on the shooter, the ammunition, gun maintenance, the conditions in which the gun is being used by the particular shooter ... and the gun, itself, which includes the magazines.
Presuming a good quality semiauto pistol, which appears in normal condition when field-stripped and inspected (and new recoil & mag springs if it's a used gun that hasn't been refurbed by an armorer, factory tech or a smith) ...
... and good quality, fresh factory ammunition is being used (I prefer to use something made by one of the major American ammo companies) ...
... and I've familiarized myself with any recommendations by a particular gun maker for a make/model (lubrication, ammunition used, etc) ...
... I like to shoot 25-50 rounds per magazine that's planned to be used with the gun.
If it's only 2 magazines being used for the initial session, then I like to fire at least 50 rounds per magazine. (After all, we're checking the condition and functionality of the magazines, which are at the heart of optimal functioning of the gun.)
I usually use whatever JHP ammunition is going to be carried for the bulk of my function testing, or, a mix of various good quality JHP ammunition that I may have on hand (that's been either issued or has been approved for optional use, in my case). I'll include some ball loads, if available, but I prefer to use JHP's to confirm normal feeding and function in semiauto pistols.
Now, in armorer classes I've attended (for a number of makes/models), a related issue of test-firing to confirm normal function after a repair is recommended. At various times this has usually been recommended as firing at least a magazine-load, or whatever "duty load-out" may be carried (typically interpreted to be a primary magazine and 2 spares, but it may be more for an agency), before the gun is returned to service.
I typically like to have the user/owner of a repaired pistol fire at least that many rounds, and have often suggested they fire more rounds, if only to satisfy themselves that their gun is now functioning normally. (When I return a repaired gun to service, it means I'm personally willing to carry/use it, but that's me.)