OK if you've got a digi SLR and the shutter you're testing has a B or T setting to do comparative exposures using the SLR shutter. Did you try it Chops? How was it?
I think the old way of photographing the TV or computer screen is as good as any method for faster shutter speeds (=<1/60th). Rick Oleson has a good description of the method
here. It also shows tapering of focal plane shutters. [Edit] 'course, I should mention, this doesn't work with them new fangled flat screen thingys.