Mocks, fakes, and stubs

Mocks, fakes, and stubs definitions

• Classification between mocks, fakes, and stubs is highly inconsistent across the literature.
  • Consistent among the literature, though, is that they all represent a production object in a testing environment by exposing the same interface.
  • Which out of mock, fake, or stub is the simplest is inconsistent, but the simplest always returns pre-arranged responses (as in a method stub).
  • On the other side of the spectrum, the most complex object will fully simulate a production object with complete logic, exceptions, etc.
  • Whether or not any of the mock, fake, or stub trio fits such a definition is, again, inconsistent across the literature.
    • For example, a mock, fake, or stub method implementation between the two ends of the complexity spectrum might contain assertions to examine the context of each call.
    • For example, a mock object might assert the order in which its methods are called, or assert consistency of data across method calls.
• In the book “The Art of Unit Testing” mocks are described as a fake object that helps decide whether a test failed or passed by verifying whether an interaction with an object occurred.
• Everything else is defined as a stub.
• Fakes are anything that is not real, which, based on their usage, can be either stubs or mocks.

Mock Object practice

• In object-oriented programming, mock objects are simulated objects that mimic the behavior of real objects in controlled ways, most often as part of a software testing initiative.
  • A programmer typically creates a mock object to test the behavior of some other object, in much the same way that a car designer uses a crash test dummy to simulate the dynamic behavior of a human in vehicle impacts.
  • The technique is also applicable in generic programming.
  • Mock objects are used to simulate the behavior of a given object in order to cope with dependencies and isolate the system under test for controlled testing.
• For more information, it is possible to use the Test Driven Development (TDD) approach without mock objects.
• A mock object is a type of Test Doubles.

Test Double

• There are at least five types of Test Doubles with some differences :
• Test Stub,
• Mock Object,
• Test Spy,
• Fake Object,
• Dummy Object

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Updated : 01/10/2021