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How to unit test abstract classes: extend with stubs?

Asked 2008-10-28T13:25:21.353
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I was wondering how to unit test abstract classes, and classes that extend abstract classes.

Should I test the abstract class by extending it, stubbing out the abstract methods, and then test all the concrete methods? Then only test the methods I override, and test the abstract methods in the unit tests for objects that extend my abstract class?

Should I have an abstract test case that can be used to test the methods of the abstract class, and extend this class in my test case for objects that extend the abstract class?

Note that my abstract class has some concrete methods.

java unit-testing testing abstract-class
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One of the main motivations for using an abstract class is to enable polymorphism within your application -- i.e: you can substitute a different version at runtime. In fact, this is very much the same thing as using an interface except the abstract class provides some common plumbing, often referred to as a Template pattern.

From a unit testing perspective, there are two things to consider:

  1. Interaction of your abstract class with it related classes. Using a mock testing framework is ideal for this scenario as it shows that your abstract class plays well with others.

  2. Functionality of derived classes. If you have custom logic that you've written for your derived classes, you should test those classes in isolation.

edit: RhinoMocks is an awesome mock testing framework that can generate mock objects at runtime by dynamically deriving from your class. This approach can save you countless hours of hand-coding derived classes.

answered 2008-10-28T14:09:27.503

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