Hey Ted. Important to have a good test chart. I usually set a camera up and place something like a dollar bill that has a lot of small detail at spacing intervals based on the distance markings on the lens. Slate one pass as by the marks, then slate another pass by the eye (and noting or taking a photo of where the lens markings are). Basically you're comparing actual focus to what the markings say it should be. Remember to measure distances from the film plane and not from the front of the lens...
Here's a little more info:
For 16mm and 35mm cameras & magazines registration tests are really important but I'm not sure how relevant they would be for Super 8 since so much of that would depend on the cartridge and they vary significantly from cartridge to cartridge. I guess you could compare two different Super 8 cameras using the same cartridge and that would give you some information on which one was more solid.