Some time ago, I have discovered, that using your own custom test double classes, instead of a test framework makes my test code more readable and maintainable. Here is an example (pseudo-code):

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function test_password_revealer_when_toggled_reveals_password() {
  passwordController = MockPasswordController.new()
  passwordRevealer = PasswordRevealer.new(passwordController)

  passwordRevealer.toggle()

  expect(passwordController.isRevealed()).toBeTrue()
}

The same test with mocking framework would look this way:

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function test_password_revealer_when_toggled_reveals_password() {
  passwordController = MockFramework.Mock.new("PasswordController")
  passwordRevealer = PasswordRevealer.new(passwordController)

  spy = spyOn(passwordController.reveal())

  passwordRevealer.toggle()

  expect(spy.haveBeenCalled()).toBeTrue()
}

If you take a closer look at the last example, and, specifically at these 2 lines:

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spy = spyOn(passwordController.reveal())

expect(spy.haveBeenCalled()).toBeTrue()

They use a language, that is not relevant to the domain, therefore, they make the test less readable.

Additionally, they have knowledge of which exactly method PasswordRevealer#toggle() should call on passwordController. If we were to rename reveal method, all tests for PasswordRevealer would fail. The same thing would happen if we were to extract methods/functions/objects out of the PasswordRevealer.

Of course, creating such test doubles yourself will involve some boilerplate code - this is a trade-off. Example:

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class MockPasswordController() {
  this.state = "hidden"

  this.reveal() {
    this.state = "revealed"
  }

  this.hide() {
    this.state = "hidden"
  }

  this.isRevealed() {
    return this.state == "revealed"
  }
}

Making this trade-off, will simplify the case when we were to change the name: we would change the name at 3 places:

• in test double class,
• in caller class,
• in “real” implementation class.

Whereas with a mocking framework, we would have to hunt for all failing tests, and usually, it means hundreds of failing tests.

Thank you!

If you, my dear reader, have any thoughts, questions or arguments about the topic, feel free to reach out to me on twitter: @tdd_fellow.

If you liked my ideas, follow me on twitter, and, even better, provide me with your honest feedback, so that I can improve.