Garden of Eden was a setup...

[Esquilax]

But the very concept that the test deals with would not even exist if the test didn't exist. What it's like is the teacher inventing a subject out of nowhere and then testing his students on this subject, that didn't exist before he wrote the test, and pretending the results of that actually means something.

Exactly.

So, what you're saying is that god created a test, bringing into existence a concept that only makes the world objectively worse in the process, where a success state could not possibly bring a benefit, and the failure state brings immeasurable suffering and pain to every living being, for no reason, and you're okay with that?

If Adam and Eve never ate the fruit, they would not only not understand the nature of sin and the test, but they wouldn't even have a concept of what sin could be. The only "lesson" that could be learned from the test is one of failure, conditional to them failing, and frankly, not only is that a lesson not worth learning, but it's also not worth the price that was paid for it.