Just what is a rank test anyway?
Through my experience, I've witnessed two main kids of tests, each with it's pros and cons.
The Rites of Passage Rank Test
This one is a test in which the student(s) basically rehash everything they've been taught since their previous rank test. Every type of stance, punch, kick, block and kata are performed over and over again. In many cases, other physical activities such as pushups are done as well.
Pros: Because these tests can last a good while (sometimes days for black belt levels), the amount of "suffering" students endures can strengthen their sense of accomplishment and make them feel that they've truly earned their rank; students get to demonstrate what they've learned; creates a feeling of tradition; easy to pass since all the students are doing is following instructions
Cons: Because these test can last a good while (heard this one before?), the level of danger can increase due to fatigue and decreased concentration (on a personal note, I can remember striking my instructor dead in his spine while testing for my black belt because I was simply too tired to focus on my control like normal); the extra stuff like pushups and running laps (yes, I've seen it...) have nothing to do with everything else; instructors have been known to do the extra stuff simply because it was done to them when they were testing themselves; demonstrating proficiency isn't the top priority
The Sample Test
A little simpler test in which the instructor has the student perform a few random requirements with a proficiency that's to the instructor's liking, the main one usually being the kata required for that belt level.
Pros: not very time consuming; students can demonstrate their proficiency level; test sticks to the curriculum
Cons: can be seen as non-traditional (taking away from the "Rites of Passage"); because the test isn't physically taxing (usually), students may not feel as though they've earned their rank