I don't usually have code that tests arguments and raise exceptions, in my code and in my customers code. As those code paths don't exist, we are not writing th

I don't usually have code that tests arguments and raise exceptions, in my code and in my customers code. As those code paths don't exist, we are not writing those tests. If a method accepts only values >= 0 (eg, square root) we test that we handle negative numbers as the documentation of the API says. That should be the same in C++. When we refactor the implementation of a web app endpoint we only test that the request still yields the response. Apparently this approach worked well enough. If somebody sends a foo instead of bar, baz or quux they'll get a 500 with the error message in the documentation and that's it.