Fakes, Stubs and Mocks
October 23, 2020
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I’m frequently asked about the difference between automated testing terms like fakes, stubs and mocks.
The term fake is a general term for an object that stands in for another object; both stubs and mocks are types of fakes. The purpose of a fake is to create an object that allows the method-under-test to be tested in isolation from its dependencies, meeting one of two objectives:
1. Stub — Prevent the dependency from obstructing the code-under-test and to respond in a way that helps it proceed through its logical steps.
2. Mock — Allow the test code to verify that the code-under-test’s interaction with the dependency is proper, valid, and expected.
Since a fake is any object that stands in for the dependency, it is how the fake is used that determines if it is a stub or mock. Mocks are used only for interaction testing. If the expectation of the test method is not about verifying interaction with the fake then the fake must be a stub.
BTW, these terms are explained very well in The Art of Unit Testing by Roy Osherove.
There’s more to learn on this topic at stackoverflow https://stackoverflow.com/questions/24413184/difference-between-mock-stub-spy-in-spock-test-framework