First the gun has to have a good reputation and not have an internal lock or magazine disconnect. I know that rarely do these features fail but they are unnecessary features and parts that really only serve, in my mind, to add failure points to a weapon(JMO, YMMV). Then it has to fit my hand well and point well for me. A good test of this is to pick a spot of object, close your eyes and point bring the gun up to a shooting position with your eyes closed and hold. If you're pretty close to "on target" than that gun points well for you. Finally I put at least 500 rounds through it, not all in one day as I find I get tired out after a couple hundred. If the gun goes through those 500 without failure(or at least none that are the fault of the gun and not something else like ammo or magazines) and shoots well for me then I would consider trusting my life to that gun.
I don't collect guns, I accumulate them.