Pressure Testing new boiler piping

[Philtrap]

I installed a new boiler and piping (with new zone valves, ball valves, back flow preventer, pump, etc.). I turned the water on and had a small leak. I fixed this failed sweated joint. The system is now charged at 12psi from the pressure reducing valve with no leaks. My question is should I pressure test the new piping or is the charge of the 12 psi good if no leaks are found over the last 4 days?

If the answer is Yes - "Do a pressure test"... can I just take off the expansion tank and place a pressure gauge in it's place and turn up the pressure reducing valve to 24 psi for some time to see if there are any leaks?

Thanks,