Those in-tank factory pumps (either TBI or EFI) are deceiving. Not only do they not carry a stamped or decal part number, the roller-impeller pump itself is only the size of a silver dollar. The rest of the assembly is the high rpm drive motor and the fuel return mechanism (if it has one). There's a fine shear-wire final connection to the motor, so if you routinely run the tank dry on payday, after 2 or 3 times the lack of gas to cool the submerged pump can overheat the motor and burn the fine wire in two.
We found this out the hard way with Judy's EFI-powered '97 Z-28 which uses the same appearing pump as the one I used, from a TBI-powered Ford Bronco. As an aside, to change pumps in a GM Z-28, the whole live rear axle & rear brake assembly must be removed, then the fuel tank to access the submerged pump- all for want of a simple 50 cent access door in the trunk. Besides the complication, the shear wire is an undocumented "feature." Not only is it theoretically dangerous to burn it out inside a tank, it is not easily repairable. I've not found a source of correct shear-wire. Luckily, the Z-28 was fixed under warranty. Unluckily, a month later the ring & pinion went out, so out came the rear end again. Second new GM I owned and the second diff I lost. GM just doesn't know how to set up a limited slip differential.
So while you could rewire a blown fuel pump with heavier gauge wire or hot-wire a new pump to check its pressure output with a bucket of water and a gauge, you can't submerge the ungrounded pump in a conducting fluid like water. I guess after thinking about it, you could use safer diesel for a submerged check. Buto don't try check-running any such pump dry for more than a few seconds even if you temporarily plumb the pump with plastic hose. Wrecking yard roll-over fuel pumps can be blown this way too, because apparently many drivers of roll-over crashes keep their foot buried while the noisy/sky/ground thing is going on.