Ah totally makes sense, I get what you mean. It is weird to make a special effort to prepare for the test, when that's sort of beside the point of what the test is about and what it leads you to demonstrate.
I can sorta understand both sides to it, on one hand, practicing the material required for the test helps build confidence, sharpens technique, helps you to understand it better, and just generally helps you feel ready for the day. Not to mention working on cardio/endurance stuff can be super helpful so you don't pass out haha..
But on the other hand, it can maybe lead to slacking off during the year, only really practicing and sharpening skills prepping for grading, then just cruising after it's done, getting sloppy in technique and convincing yourself that you are that grade. But depends on the individual I guess (and instructor, how they've taught and what's expected in class). Can also lead you to think that the test is the be all end all, and can take the focus away from the journey that you're on day to day. Gradings aren't necessarily the pinnacles (they can happen just during normal training sessions), although I consider them milestones of a sort.
The majority of gradings I've undertaken have not only been a test of technique, knowledge, understanding, ability etc, but a really heavy focus on endurance, perseverance, and a fighting spirit. So yeah in a sense, it would make sense not to do any 'prep', so that that can be really tested, but in another sense training hard in prep for it means you can push a bit harder in the test..
Great food for thought Gerry! Never pondered it along those lines before!