Please don't test a pressure vessel by pumping any gas into it. If it fails it will basically explode!
If you want to test any vessel you do it with a liquid medium, either water or a hydraulic fluid, if corrosion is a problem.
Normally you test to twice the working pressure but for higher pressures this may be considered excessive.
One reason I do not use pneumatics in my robot is I don't think I can prove it safe in a robot. after every fight.