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Friday, April 28, 2006

Fake Dummy Mocks Stubs

Gerard Meszaros has come up with a new name for the mocks, fakes etc. - objects that are used in the place of actual objects while testing. In his soon to come book titled XUnit Test Patterns, he proposes a new name - Test Doubles for all these objects. While Test Double covers the general set of objects used to represent a real time object during testing, there are four different types of Test Doubles vis-a-vis:
  • Stub: Programmed (by the test automater) to respond to calls made during the test (and only the calls used for the test). Test Stub returns pre-defined values (inputs, with expected outputs). Used to test indirect inputs.
  • Mock Object: Represent test doubles used to test the outputs (in an indirect way). A mock object is designed to expect certain calls from the system under test, failing which the mock object throws an exception (thus failing the test). In other words, mocks are used as indirect way to test the outputs of the system under test.
  • Dummy Parameter: A dummy (or placeholder) is used to fill parameter lists and are not used anywhere else.
  • Fake Object: Fake objects provide the same functionality as the real object, but uses "shortcuts" to obtain the results. Fake objects are only used to speed up testing and avoid probable side-effects.
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