or the existing test cases are not really unit tests. Unit tests should be on the smallest practical units, otherwiseyour methods can change without breaking the tests while some poor userusing your methods will have their code break.
How does it help if a unit test specifically calls a particular piece of API as opposed to the API is used internally?
In both cases the API is being tested similarly thoroughly.If I want to change the API, in both cases I change the class and then change some bit of code somewhere calling it. In either case, the the user is screwed if documentation of the change does not make it to them somehow. It only makes a difference if users are monitoring unit tests for evidence of changes. I have trouble imaging anyone doing that given that we have the doxygen docs and a commit list (and eventually, presumably, nice a human readable list of changes).
And given the current state of our unit test code, I hope no user looks at them for anything.