Question for all the @rustlang hackers out there -- Do you prefer #[cfg(test)] stuff in your crate, or code in the tests/*.rs files for testing the majority of your code when your library is almost entirely public API?

The first is a unit test, whereas the second is an integration test. You'll always want both — unit tests for private internals, and integration tests for testing the API.

Yeah, but where do I draw the line when 99% of the API is public? Do I bother with unit tests for specific testing, or do I try and cover all the code by means of integration tests? What about examples, do they count for coverage, or not? Such are my Monday evening ponderings.

I consider doc tests separate from unit/integration tests. To me, those are more for validating that the user friendly docs are actually correct, while my unit tests and integration tests cover all of the other cases.