I'm sure there is a test proceedure out lined somewhere along with a special guage to read the pressure output of the pump ..... but if the car idles fine on a negative incline (fuel in the tank higher than injector lines) and dies with the fuel level below the injection pump, plus the fuel filters are new and the lift pump has more than 150k miles on it, that would be enough evidence for me (shade tree mechanic) to replace the lift pump. Good Luck!