Fuel pump testing

So I was having issues with it running. It has been sitting a while due to a bad alternator (fixed now bought a new one). I was able to start it at first and it was running but only for a few minutes until it would shut off. Wouldn't start right away (almost like it was to hot). Changed the thermostat and still same issue. Changed my plugs and it started but shortly after shut off again and wouldn't start afterwards. I checked fuel pressure, (wasn't any) I then changed my fuel filter since I already had a new one and it was easier than dropping the fuel tank. Still no start so I've dropped my fuel tank removed my fuel pump and I'm now trying to test my fuel pump before I buy a new one (cause I can't afford it) but when I reassembled the pump (disassembled to make sure it was clean of trash) I've got it in the fuel pump assembly and dropped it in a tub of fuel. When I put power to it, it's bubbling from the bottom not the bladder part the pump itself and white smoke or vapors are in the bubbles but only after I leave the power to it for a couple minutes. (Shut it off due to smoke/vapors.) But it never started pumping any fuel. Is this normal and should I go ahead and keep the pump running until it pumps fuel or not?