Can I use jmock to replace an implementation returned by a factory?

Question

I have a factory that returns an interface FormatService:

public class FormatServiceFactory {
    public FormatService getService() {
        ...
    }
}

Is it possible to mock out this factory so that it will always return a stub implementation of FormatService - FormatServiceStub in our unit tests?

Answer 1

Depends. How is the factory obtained/used by the code under test?

If it's instantiated explicitly in the methods you're testing, or if it's a static factory, you won't be able to mock it.

If it's injected into the object under test, you can create and inject the mocked factory before executing the test.

Mocking the factory should be easy enough with JMock. From your example code, it looks like it's a class, not an interface, so you'll either need to use the cglib version of JMock and the MockObjectTestCase class in the cglib package for JMock 1, or the ClassImposteriser for JMock 2.

Once mocked, you can make it return your stubbed implementation (or even a mock FormatService) when you define the expectations for the getService() method.

Answer 2

Mockery mockery = new JUnit4Mockery() {{setImposteriser(ClassImposteriser.INSTANCE);}};

final FormatServiceFactory factory = mockery.mock(FormatServiceFactory .class);

context.checking(new Expectations() {{ oneOf (factory ).getService(); will(returnValue(new FormatServiceMock())); }});