Unit tests as documentation

Just write the docs. A simple template:

- What is it?

- What does it do?

- Why does it do that?

- What is the API?

- What does it return?

- What are some examples of proper, real world usage (that don't involve foo/bar but instead, real world inputs/outputs I'd likely see)?

Why is a hard question.

And what should be obvious or it’s still too complex.

If why is hard it may not need to exist. For example:

"This function exists to generate PDFs for reports and customer documents."

"This endpoint exists to provide a means for pre-flight authorization of requests to other endpoints."