This is the easiest/fastest way I've discovered to do a check.
on a cold engine, start and run for a minute, then shut down and monitor fuel pressure with a diagnostic tool. so shut down and turn on power without starting.
the purpose of running a short while on a cold engine is that there's some heat in the block, that will then spread to the injectors and heat up the fuel in them after shut down. If there's no leaks, you will see the pressure steadily rise, if the pressure stays the same or drops you have a small or bigger leak.