> That is still dependent on the controller's design. If that changes, behavior might change without the tests ever detecting that.

The unit tests are (primarily) to cover enough branches that I feel confident the controller works. If (when?) parts of the controller code is changed, I would expect part of the review ensures these new additions are adequately tested. If I just go adding random combinations "just in case", I am really only adding additional maintenance overhead (tests are not free after all) with no provable benefit to the present (and no provable reduction against future risks).

> At least that one case is important.
I can see the use of adding that particular case :)