- 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)?
But then I realized that a lot of what makes a set of tests good documentation is comments, and those rot, maybe worse than dedicated documentation.
Keeping documentation up to date is a hard problem that I haven't yet seen solved in my career.
In the documentation, you can include code examples that, if written a certain way, not only looks good when rendered but can also be tested for their form and documented outputs as well. While this doesn't help with the descriptive text of documentation, at least it can flag you when the documented examples are no longer valid... which can in turn capture your attention enough to check out the descriptive elements of that same area of documentation.
This isn't to say these documentation tests are intended to replace regular unit tests: these documentation tests are really just testing what is easily testable to validate the documentation, the code examples.
Something can be better than nothing and I think that's true here.