I've never seen this as a problem. If you're doing TDD and you have a scenario in mind, you describe that scenario in the name of the test.
If you're writing the test after then yeah, maybe it's hard, but that's one of the many reasons why it's probably better to write the test before and align it with the actual feature or bugfix you're intending to implement.
Maybe also why TDD is hard for me because I only truly start to think or visualize when I'm writing the actual code. I don't know if it's ADHD or what it is, but writing requirements, tests before hand, is just not my forte. It's like I only get dopamine from when I build something and everything else feels frustrating.
I used to be like that sometimes. Then I started realizing I'd get the function 90% complete and discover an edge case and have to start over in a way that could handle the edge case. Sometimes this could happen twice.
Documenting your requirements by writing the tests in advance is of course painful because it forces you to think more upfront about the edge cases in advance. But that's precisely why it saves time in the long run, because then it makes it a lot more likely you can write the function correctly from the start.
If you're writing the test after then yeah, maybe it's hard, but that's one of the many reasons why it's probably better to write the test before and align it with the actual feature or bugfix you're intending to implement.