if that is the only testing you do I agree. However to test that the code works as the docs say is valuable as well. The code often will do more, but it needs to do at least what the docs say.
Agreed. Catching mismatches between doc and implementation is still valuable, just wouldn’t want people to rely on it as a safety net when the docs themselves might be inaccurate/incomplete. As a complement to traditional tests though seems like a solid addition.