What's the best way to test my fuel solenoid without taking it out of the car? I'm running a FPSS and a MSD digital WS.

Take off the line from the solenoid to the nozzle and let it rip. You may need a bucket, rags, blast goggles..etc. You will need to take off the WS or atleast id recommend doing that

^ Check to see if you have power going to the noid when you hit the switch... first things first.

Then if there's power going there, it 'should' work.. in theory..