I am very wary of fuel-related fire dangers, so I prefer to work with Diesel when I test fuel pumps. The Diesel has no materially adverse effect and it’s safe.
I test inline fuel pumps by sticking a hose on each end, and then sticking each hose into a can that’s part-way full of Diesel fuel. Then, I hot-wire the pump terminals using a stand-alone workbench 12V battery that has some alligator clips (and an inline fuse) as part of the wiring.
If all goes well, the pump makes a noise like an electrical motor is running (mostly because it is) and it sucks fuel from one can and pumps it into the other can. I use two cans in case I mix something up by mistakes, so I don’t ever run the fuel pump without fuel in it, since that’s a way to overheat and kill the pump.