Pressure test a rudder ?

[Snowgoose-1]

Why bother in the first place?
Does your rudder need to be watertight?
Would there be a possibility that applying such pressure may break the bond between foam & outer skin?
Would the joint to the shaft of GRP & aluminium, or steel, at the top, actually hold much pressure & if broken, make leaks more likely?
Would the test weaken the joint between the 2 halves, such that later the rudder split in half?

Just thought it might be worth an ask if any other folks have tried it whilst it is off the boat. Weight is a factor . It's a lifting keel boat and although the keel is hydraulic, the rudder is manual. Perhaps buoyancy of the rudder might also be a factor on a light boat.