Shooting tests with your camera may seem like a hassle and an unnecessary waste of time and money but it is neglible when you compare it to the cost of a reshoot (if a reshoot is possible.) Most camera rental houses post disclaimers which protect them from liabilty. It is always smart to check your camera at the rental house before your shoot.
Scratching
Load a dummy roll of undeveloped film into your camera and run it through. Inspect the roll with a magnifying glass for any scratches on the films surface.
Registration
Shoot 100ft of a grid of white lines against a black background, being careful not to move the camera or background during filming. Rewind your film and slightly offset the lined background and expose the film again. Develop the film and then project it. If there is a problem with the registration, then the white lines will shift against each other.
Light Leaks
Load an unexposed roll of film into your camera. Make sure to cap the lens and all other openings on the camera. Bathe the camera in bright light and run the roll of film. Check the developed film for any light leaks.