Should you only mock types you own?

by

My answer is “no”. You should mock anything that makes sense in the context of a given unit test. It should not matter if you “own” the mocked type or not.

These days, in a Java or .NET environment everything (and I really mean everything) can be easily mocked. So, there is no technical reason to go to the trouble of first writing extra wrapper code.

Some additional ideas I have been thinking about recently (November 2010), that show how illogical to “only mock types you own” can be:

  1. Suppose you do create a wrapper for a third-party API, and then you mock the wrapper in unit tests. Later, however, you figure the wrapper can be reused in another app, so you move it to a separate library. So now the wrapper is no longer “owned” by you (since it is used in multiple apps, potentially maintained by different teams). Should developers create a new wrapper for the old one?!? And keep doing it recursively, adding layer upon layer of essentially useless code?
  2. Suppose somebody else already created a nice wrapper for some non-trivial API and made it available as a reusable library. If said wrapper is just what I need for my specific use case, should I first create a wrapper for the wrapper, with a nearly identical API, just so I will “own” it?!?

For a concrete and realistic example, consider the Apache Commons Email API, which is nothing more than a wrapper for the standard Java Mail API. Since I don’t own it, should I always create a wrapper for the Commons Email API, whenever I write unit tests for a class which needs to send e-mail?

More Related Contents:

  1. Swagger/OpenAPI mock server
  2. What are the differences between mocks and stubs on Rhino Mocks?
  3. How to mock a Kotlin singleton object?
  4. jquery (or pure js) simulate enter key pressed for testing
  5. How do I use Moq to mock an extension method?
  6. What’s the best mock framework for Java? [closed]
  7. Using Mockito with multiple calls to the same method with the same arguments
  8. How to properly match varargs in Mockito
  9. How to tell a Mockito mock object to return something different the next time it is called?
  10. How do you mock out the file system in C# for unit testing?
  11. Mock functions in Go
  12. Python: Mocking a context manager
  13. PHPUnit Mock Objects and Static Methods
  14. How can one mock/stub python module like urllib
  15. Mockito test a void method throws an exception
  16. Mocking Java enum to add a value to test fail case
  17. How to test a mocked JNDI datasource with Spring?
  18. How can I mock user input (from “input” in 3.x, or “raw_input” in 2.x) for a unit test?
  19. How to change the behaviour of a mocked import?
  20. What is the best way to unit-test SLF4J log messages?
  21. How to monkeypatch python’s datetime.datetime.now with py.test?
  22. Moq: unit testing a method relying on HttpContext
  23. Why are my mocked methods not calld when executing a unit test?
  24. How to test or mock “if __name__ == ‘__main__'” contents
  25. How do I mock a class without an interface?
  26. How to mock Controller.User using moq
  27. Unit testing a python app that uses the requests library
  28. Difference between Dependency Injection and Mocking Framework (Ninject vs RhinoMocks or Moq)
  29. python: mock a module
  30. Mocking behaviour resets after each test with PowerMock

Leave a Comment