In TestDrivenDevelopment, generally the UnitTestIsTheMock is a good practice to DoTheSimplestThingThatCouldPossiblyWork.

This is basically just saying that the UnitTest itself acts as the object interacting with the object(s) under test.

This is a response to seeing more common instances of ExpensiveSetUpSmell''''''s.

For example, MockingLegacyCode '''may''' be the best way to get quickly to UnitTestingLegacyCode. But, generally less MockObject''''''s is probably better. You don't want to leave a lot of MockObject''''''s around for long because they preserve the CodeSmell, rather than ImprovingTheDesignOfExistingCode.

In contrast, if you have an expensive object involved in one or more UnitTest''''''s, such as a file or database, a MockObject is often the best way to improve the testability of the object(s) under test.

--JasonNocks

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I have seen this called SelfShuntPattern -- AnthonyWilliams

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CategoryMockObjects