Disregarding the "code is doc" position, it's still common to have an overview or index for documentation, which points readers in the right direction instead of dumping pages of detailed docs on them.
Now, you could also have a well organized test suite that goes from most obvious to most detailed, split into sections for each use-case, but this sounds a lot more tedious than "write a one-line comment describing the unit test".
Now, you could also have a well organized test suite that goes from most obvious to most detailed, split into sections for each use-case, but this sounds a lot more tedious than "write a one-line comment describing the unit test".