The shut off solenoid could always fail without notice, but it's rare. That style will have a rubber plunger on the end that blocks fuel flow through the pump when no power is applied. You can try to remove the unit and bench test it, but be sure to clean off the area around it before doing so. Disturbing the solenoid will stir up whatever crud has accumulated around it. Removing it will open up a passage for some of that to jump right into the now vacant hole. I've seen a few units of that type fail, and have removed the rubber plunger and put the unit back in on occasion to allow the engine to run. You have to find an alternative means of stopping the engine, like shutting it off in gear and holding the brakes. Awkward, yes, but it allows one to get the engine running and/or prove that the unit works or it doesn't.