pressure testing used hot water heater?

how do you pressure test a used cast iron hot water radiator prior to installing. The radiator manufacturer is American Radiator. It is an upright radiator made up of 20 segments, total o.a. 10" wide x 20'' high x 54" long and was manufactered in early 1900. Water connections are at each end on the lowest point of the heater and are bled at the top on one end.