I went and read that OSHA chapter cited on the ROPS tag. (OSHA 1928.52). For those who like detail:
It looks like the ROPS is tested with a pendulum weighing slightly more than the rated ROPS capacity. The pendulum is suspended 25 ft above. It is swung back until its center of gravity is 1 ft higher than the point where it will impact the ROPS. If I understand what I read, this gives a 4200 lb pendulum 4200 ft-lbs of energy when it strikes.
One impact is made from the rear then another from the side. To pass, the momentary maximum deflection of the ROPS has to remain outside the operator space.
There's an alternate test method. The tractor is started up a 60 degree ramp causing it to flip backward. Then its driven 10 mph toward a ramp on one side which flips it on its side. It seems to me this moving rollover would stress the ROPS more than the pendulum test. Only one of the series, the driving or pendulum series, must be passed to prove conformance.