An instructor is going to run their dojo the way they want but what Im saying is that, if an instructor is going to require patience as one of their requirements for belt advancement, why not just require a minimal length of time, within reason of course, that the student has to have their current belt before they can get their next belt, and after they've fulfilled that minimal time requirement, let the student test for their next belt? Now, if an instructor is going to require not only time but also skill in order to promote, as most instructors from my observations do, that's what the test is for, to see if the student is skilled enough for the next belt. Taking a test doesn't guarantee you will pass otherwise it wouldn't be a test. So that's what the test is for, to see if the student has the skill.
In my original post I was talking about a brief message board chat I had with a martial arts student on a martial arts forum that wasn't this one. From what little I learned from our brief chat, his instructor told you when you would test because he required patience to promote, not just skill, so even if you were skilled enough to test he might not tell you that you could test because he wants you to be patient. What I don't get is why an instructor would do that instead of just setting up a minimum time requirement, and that after you fulfilled the time requirement you could then test.