Well I would say the fuel gauge would not show the correct fuel level. You would have loss of power.intermittent fuel flow and you would not hear the fuel pump kick on when the key is turned to accessories.you turn the key on and have someone listen near the fuel tank for a whining motor sound this will tell you if your pump is even working or not. The only other thing to do is to test the fuel flow from the line coming out of the tank.you could have a fuel pressure(from jeg's,summit racing,any auto parts store) gauge put in line to tell you what the pump is actually doing.I guess you could also see if the pump is actually getting power by checking the wires with a continuity meter/gauge. All this can be done without dropping the tank and replacing the fuel pump. Now if your pump is manual basically you would have no fuel flow at all.you would not be able to start the vehicle.this is all I can think of .