Pressure testing radiator system with expansion tank

I would like to pressure test a closed hydronic radiator system that has an expansion tank on it. I can detach the furnace, shut the water supply, and then mount a gauge with a nozzle on it that I can pump to something like 15-20 psi of compressed air and hope it keeps the pressure, meaning no leaks. I've done that with my gas pipes before successfully.

I am only concerned about the expansion tank. Should I remove it and put a plug in its system socket, or can it withstand that kind of pressure? I'm afraid of it exploding.