Testing like he describes is viable. And you will be testing the pump at it's normal operating voltage ( although at a reduced test pressure )

With engine off, voltage will be down 2v or so, which makes a good difference. Or you could call it a safety measure for the purposes of the test.

If doing it for 1 minute, make sure you have a big enough container.

You could power the pump manually, adjust fuel pressure to say 70-80psi and measure flow out the return.


Of course another check you can do is find out what your fuel pressure is currently doing under load. If it's holding stable with boost then chances are the pump is coping fine.
And also ensure you are getting 14v at the pump at all times.