A driveshaft assembly, for example in an Electronic Unit Injector, Unit Injector or Electronic Unit Pump testing machine, wherein an indexing means, such as complementary external and internal splines, enables a cam to be mounted on a shaft at a number of discreet positions, each providing a different offset of a central axis of the base cylinder section from a central axis of the shaft, each position providing a different maximum lift value of a plunger in contact with the cam, directly or via a rocker arm.