Today I found a neat trick for diagnosing a fuel pump. I removed the inlet line, and attached a length of tubing with a funnel jammed in the end. I secured the funnel and filled it to the top with fuel.
I loosened the inlet line to the carb and cranked the motor. I was able not only to confirm the pump was pumping fuel, but the tubing and funnel acted as a stethoscope, I could actually hear it sucking fuel.

Way easier than pulling the pump to verify function by manually operating it.