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Why I Don't Like Mocking Frameworks

Disclaimer: By mocking framework I generalize anything that includes support for stubs and mock objects.


The use of mocking frameworks was a difficult part of my TDD journey. Not only are newcomers expected to get their head around the basics of the practice there are now new tools to contend with. To make matters worse there is a lot of mocking frameworks out there with differing quality qualities and suitability.

The use of mocking frameworks includes a variety of disadvantages.

  • Readability suffers in most cases. You often find yourself asking what is exactly happening here? The frameworks themselves usually impose these constraints and make the issue worse.
  • The use of frameworks tends to lead to header interfaces and not role interfaces being used. IDE's usually have a factor in this as they make this anti pattern so very easy to introduce.
  • A lot of developers are not aware of what these frameworks are doing behind the scenes. This can lead to confusing tests and a general lack of understanding.

Solution

My preference is to use hand crafted test doubles. While these are looked down upon by some, they offer numerous benefits.

  • Stubs and Fakes are easier to understand, write and maintain when hand crafted.
  • Manual test doubles read easier. The key benefit here being able to name implementations after their use and function.
  • Hand crafted test doubles promote reuse. It is likely that such doubles will be used across numerous tests. Once created code duplication actually reduces.
  • Hand crafted test doubles are a prerequisite to enable contract testing.

The actual implementation of these hand crafted doubles is minimal. In most cases simply providing the arguments as constructor or method parameters works. For more complicated scenarios DAMP tests can be used.

One area where frameworks provide a benefit is that of mock objects. In non trivial examples the requirements to verify numerous parameters and configurations can be verbose to hand craft. However there are alternatives to hand crafted test doubles such as the self shunt pattern which will be expanded upon in a future post.

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