What is the best way to use Guice and JMock together?

Posted by Yishai on Stack Overflow See other posts from Stack Overflow or by Yishai
Published on 2010-01-11T21:14:06Z Indexed on 2010/04/05 5:23 UTC
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I have started using Guice to do some dependency injection on a project, primarily because I need to inject mocks (using JMock currently) a layer away from the unit test, which makes manual injection very awkward.

My question is what is the best approach for introducing a mock? What I currently have is to make a new module in the unit test that satisfies the dependencies and bind them with a provider that looks like this:

public class JMockProvider<T> implements Provider<T> {
    private T mock;

    public JMockProvider(T mock) {
        this.mock = mock;
    }

    public T get() {
        return mock;
    }
}

Passing the mock in the constructor, so a JMock setup might look like this:

    final CommunicationQueue queue = context.mock(CommunicationQueue.class);
    final TransactionRollBack trans = context.mock(TransactionRollBack.class);
    Injector injector = Guice.createInjector(new AbstractModule() {
        @Override
        protected void configure() {
            bind(CommunicationQueue.class).toProvider(new JMockProvider<QuickBooksCommunicationQueue>(queue));
            bind(TransactionRollBack.class).toProvider(new JMockProvider<TransactionRollBack>(trans));
        }
    });
    context.checking(new Expectations() {{
        oneOf(queue).retrieve(with(any(int.class)));
        will(returnValue(null));
        never(trans);
    }});
    injector.getInstance(RunResponse.class).processResponseImpl(-1);

Is there a better way? I know that AtUnit attempts to address this problem, although I'm missing how it auto-magically injects a mock that was created locally like the above, but I'm looking for either a compelling reason why AtUnit is the right answer here (other than its ability to change DI and mocking frameworks around without changing tests) or if there is a better solution to doing it by hand.

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