Vacuum advance is easy to test. If you are not afraid you can apply suction to the port, the arm should move. Block the port with suction and it should stay. I use my tongue to block the port, and lungs to provide the suction, but then I am old and not afraid I will get any ill effects from the procedure. If it leaks, you can feel the vacuum drop. If it has failed, it won't move the lever. About as simple a test as you can get.
