Research can be key, if you know a robot with similar armour have a look at it and see where its bending ect.

Otherwise, any destructive test you do is likely to be either insufficient or.... destructive.

The only exception being internal testing, ie driving your robot against a brick wall for a fight length to test the components under load. Or testing any weapon against objects bigger/more solid than what their likely to come up against (the standard beetle test is my old Ti featherweight chassis).