Roy Smith <[EMAIL PROTECTED]> writes: > The only externally visible interface is pushTheButton(), yet you > don't really want to call that during testing. What you do want to > do is test that a random city really does get picked.
Then what you're really testing is the interactions of the "push the button" function with its external interface: you're asserting that the "push the red button" function actually uses the result from "pick a random city" as its target. Thus, the "pick a random city" function is being defined by you as *interface* for the "push the button" function. Interfaces do need to be unit tested. This is done by having the unit test substitute a test double for the "pick a random city" function, rigging that double so that its behaviour is deterministic, and asserting that the "push the button" function uses that deterministically-generated result. It's at this point, of course, that the "pick a random city" function has come rather close to being public API. The designer needs to have a fairly good reason not to simply expose the "pick a random city" function in the API. > You can do one of two things at this point. You can say, "But, > that's not part of the externally visible interface" and refuse to > test it, or you can figure out a way to test it. Up to you. Note that the only thing I'm saying one shouldn't do is unit test the private function *directly*, since the design decision has been made that it's not part of the API. The *behaviour* of the function, as exposed via the "push the button" piblic API, should certainly be unit tested. Any behaviour of that function that's *not* exhibited through the behaviour of some public API should *not* be unit tested, and should in fact be removed during refactoring -- which will not break the unit test suite since no unit tests depend on it. Alternatively, as above, the design decision can be made that, in fact, this function *is* part of the public API since external things are depending on it directly. Then it needs full direct unit test coverage. -- \ "I got contacts, but I only need them when I read, so I got | `\ flip-ups." -- Steven Wright | _o__) | Ben Finney -- http://mail.python.org/mailman/listinfo/python-list
