For a reputable manufacturer of semi auto I like to do at least 150 FMJ and 50 of my specific chosen JHP round before considering it for carry, but I prefer and generally get more than that. Basically two range trips of about 100-150 round each time, with at least 50 and possibly as many as 100 of the specific JHP load. That's for a new gun.
If it's an established gun that has proven reliable for me already, and I'm just switching to a different defensive/JHP round, about 30-35 or so rounds might be all I test (box of 50, leave enough to fill one magazine once, shoot the rest).
STORY TIME
I once bought a new Glock 30SF. I took it to the range and fired something like 100 FMJ and a 50 round box of Winchester Ranger Talon. I then loaded it up with Winchester Ranger Talon +P (RA45TP, the first 50 had been RA45). Next range trip I shot the RA45TP that had been in the gun, and I had two failures out of 11 rounds!
It turned out to be a lemon, it would not reliably work with JHP, trying 100+ Ranger as well as HST. Sent to Glock, got it back, still bad, exchanged it with Glock for a G21 SF that was perfect.
So, yeah...test that stuff before you trust it...