Noam Raphael wrote:
But what about the unit tests? They would have still reported a success - where of course they shouldn't have; my classes, in this stage, didn't do what they were expected to do. This problem might arise even when not changing the interface at all - it's quite easy to write a class which, by mistake, doesn't implement all the interface. Its successful unit tests may check every single line of code of that class, but a complete method was simply forgotten, and you wouldn't notice it until you try the class in the larger framework (and, as I understand, the point of unit testing is to test the class on its own, before integrating it).
Except that unit tests should be written to the *specification*, not the implementation. In other words, forgetting a complete method would require that you forget to write the method, *and* that you failed to translate the specification into unit tests *for that same method*.
In the context of changing an existing interface, a unit-testing scenario would mean that, instead of installing a "pure virtual" method on a base class, you'd change the unit-tests to follow the new specification, and then write code that would pass the unit tests. If you are subclassing from a common base, then you'd only need to change the unit test for that common base class (presuming that all derived classes would run those unit tests as well).
Jeff Shannon Technician/Programmer Credit International
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