Mocks Aren’t Stubs

I’ve just read a really interesting article by Martin Fowler ‘Mocks Aren’t Stubs‘. This lead me to the conclusion that I have also been confusing the terms mocks and stubs. To try and summarise the key difference between mocks and stubs is chiefly that of testing behaviour and/or state. Testing state means that you are only interested in the final outcome of the objects and their eventual state, and not all how they reached it; Testing behaviour means that you are instead interested in the behaviour of the objects and how they got to their final state. A stub will not, in general, support testing of behaviour, whereas a mock is fundamentally all about behaviour testing.

So in my previous post “Mocking without a mocking framework” I was really talking about stubbing. Specifically combining Dependency Injection with (dynamic?) stubbing to support testing.

I think a really interesting question is “do you want behaviour testing?” It seems unnatural for a test to care how an object came up with its answer.