Fowler on the distinction of Mocks v Stubs

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Fowler on the distinction of Mocks v Stubs

Thu, 01/18/2007 - 09:31 — charlie.collins

Mocks Aren't Stubs

I first came across the term "mock object" a few years ago in the XP community. Since then I've run into mock objects more and more. Partly this is because many of the leading developers of mock objects have been colleagues of mine at ThoughtWorks at various times. Partly it's because I see them more and more in the XP-influenced testing literature.

But as often as not I see mock objects described poorly. In particular I see them often confused with stubs - a common helper to testing environments. I understand this confusion - I saw them as similar for a while too, but conversations with the mock developers have steadily allowed a little mock understanding to penetrate my tortoiseshell cranium.

This difference is actually two separate differences. On the one hand there is a difference in how test results are verified: a distinction between state verification and behavior verification. On the other hand is a whole different philosophy to the way testing and design play together, which I term here as the classical and mockist styles of Test Driven Development.