Well it depends on how they do the test. The measurement already take all those into account. Typically on race cars, you do a torsion test from hub to hub. You replace the suspension with solid members, then fix both wheel on an axle on a fixture through the hubs, then support the front end over a pivot of somesort(but not fixed, just a point support), then load one of the wheel of the other axle with a known load, then measure the deflection. Based on the load, the length of the moment arm(point which the load applies to the chassis centerline), and the deflection you arrive at a value. This measurement takes into the account of the compliance of the suspension members also. You can also fix the chassis on a table without suspension components and load the opposite end of the chassis and do the same measurement, which does not take suspension compliance into the account.