I am a little confused by people's responses that these Dan gup tests keep black belts focused and/or are maintenance tests in preparation for the next dan test. At my school, the head instructor has final say on whether any student can test, colored belts or black belts. If you are attending class regularly and putting in the effort your instructor should know if you are ready for the next test. A maintenance test, at least in my eyes, would mean your instructor is not sure if you are ready (i.e. has not been paying attention to your training), or as the OP said, is trying to generate additional revenue. If in the span of time between dan tests you can't find anything that you need to improve, then you're not being honest with yourself. No maintenance test is going to help with that problem.