What to do when Java Best Practices conflict with Mockito

Question

My development team has started to use Mockito and have classes that have been defined as 'final'. I've read in Effective Java by Joshua Bloch and in the SO thread When to use final that all classes should use the final modifier. There have been some disagreement in the thread, but I do agree with the idea of forcing class composition unless inheritance makes sense.

What should I do when I want to test classes using a testing framework like Mockito that requires classes to not have the 'final' modifier? I'm hoping someone else has encountered similar issues during their development. What resolutions did your development team arrive on?

There are two obvious answers such as using JMock or remove the 'final' modifier on the classes we want to test, but we want to stick with one external testing framework (besides JUnit) and it may be hard to convince other developers to remove the 'final' modifier.

Thanks.

Answer 1

What do you need most:

1. The ability to make sure that somebody doesn't inherit from your class, OR
2. The ability to make sure that your code is testable using your mocking framework of choice?

Generally, I believe that you don't need to enforce (1). For me, testability (2), is far more important. What fits your situation best?

Answer 2

If you want your classes to be final you can have them implement interfaces. The interfaces are mockable.

Answer 3

As already mentioned in the other answer you can make your final classes to implement interface(s) and in your tests mock the interface(s).

This is one of the benefit of using Mock objects; in scenarios like this they make you to think about how the code can be better organized. If your code base has lot of reference to final classes (thus binding to concrete implementation) it violates the OO principle of "programming to an interface" and the need of better testability would help you to think of refactoring to eliminate dependency on concrete implementations.

This paper on usage of Mock Objects Endo-testing: Unit Testing with Mock Objects has a section (4.4) titled Interface discovery that explains how mock objects help in discovering the interfaces.