How do I find out if my fuel pump isnt working?

If its the injector pump, then I believe that it requires to be rig bench tested under load, because of the precision required to deliver fuel at the right time & required high pressure into the cylinder.
The best plan is to eliminate all alternatives as these pumps are not cheap!
1. Is the tank pump working or fuel lines, fuel filter blocked with wax?
2.Air leaks in the fuel system? Reprime the system.
3.ECU fault, read off the codes. Note that the fuel pump ecu will not show its codes.
4.Check for continuity to the connections, the fuel pump pcb see's a lot of thermal cycling & so fatigue that generate dry joints. It may be a good idea to check and clean connections to the pump ecu's, sensors & protect with dielectric grease.
5.Apart from checking there is fuel in the tank (obvious but it does happen), make sure that the tank breather is clear.

If after all of this it still fails you might have to bite the bullet or sell the car.
This is not a fully comprehensive list, I'm sure that there must be other tests, I do advise talking to your garage, go on to forums just in case.