How to unit test a class which extends/inherits a 3rd party class

Question

I have created a new class which extends a 3rd party abstract class. The new class calls methods in the abstract class. The problem I have is when trying to write the unit test, I'm not sure how to write a test as I would not know the exact details the 3rd party class requires.

The AbstractDecoratorMapper below is a SiteMesh specific class which I have to extend for SiteMesh to work correctly. As far as I can tell from the documentation I can't use composition.

public final class PartnerDecoratorMapper extends AbstractDecoratorMapper {

    @Override
    public void init(Config config, Properties properties, DecoratorMapper parent) throws InstantiationException {
        super.init(config, properties, parent);
    }

    @Override
    public Decorator getDecorator(HttpServletRequest request, Page page) {
        if (super.getDecorator(request, page).getName().equalsIgnoreCase("default")) {
            return getNamedDecorator(request, "externalPartnerDefault");
        }
        return super.getDecorator(request, page);
    }
}

I use JMock if there is anything this tool can do to help.

Answer 1

You don't need to know details from 3rd party libs... you just need to mock them returning something you expect from them.

In the case you are inheriting it you could setup the class as it will be used on production and invoke the methods that should be invoked in regular uses. All that you need to check is if the result is as you expect. (you don't need to know exactly how the 3rd party classes works on the test).

In order to check if all code you implemented was executed you can use a plugin to check the coverage like eclemma - http://www.eclemma.org/ )

Answer 2

With JMock, you can't to the best of my knowledge mock calls to a superclass of the class under test.

The answers to this related question may be useful, but the main answer is to switch to a mocking framework (JMockit is suggested) that does support this.