Can I mock a super class method call?

Question

Sometimes, you want to test a class method and you want to do an expectation on a call of a super class method. I did not found a way to do this expectation in java using easymock or jmock (and I think it is not possible).

There is a (relative) clean solution, to create a delegate with the super class method logic and then set expectations on it, but I don't know why and when use that solution ¿any ideas/examples?

Thanks

Answer 1

Well, you can if you want to. I don't know if you are familiar with JMockit, go check it out. The current version is 0.999.17 In the mean time, let's take a look at it...

Assume the following class hierarchy:

public class Bar {
    public void bar() {
        System.out.println("Bar#bar()");
    }
}

public class Foo extends Bar {
    public void bar() {
        super.bar();
        System.out.println("Foo#bar()");
    }
}

Then, using JMockit in your FooTest.java you can validate that you're actually making a call to Bar from Foo.

@MockClass(realClass = Bar.class)
public static class MockBar {
    private boolean barCalled = false;

    @Mock
    public void bar() {
        this.barCalled = true;
        System.out.println("mocked bar");
    }
}

@Test
public void barShouldCallSuperBar() {
    MockBar mockBar = new MockBar();
    Mockit.setUpMock(Bar.class, mockBar);

    Foo foo = new Foo();
    foo.bar();

    Assert.assertTrue(mockBar.barCalled);

    Mockit.tearDownMocks();
}

Answer 2

Expanding on @Cem Catikkas answer, using JMockit 1.22:

@Test
public void barShouldCallSuperBar() {
    new MockUp<Bar>() {
        @Mock
        public void bar() {
            barCalled = true;
            System.out.println("mocked bar");
        }
    };

    Foo foo = new Foo();
    foo.bar();

    Assert.assertTrue(mockBar.barCalled);
}

No need for the static class annotated with @MockClass, it is replaced by the MockUp class.

Answer 3

I don't think I'd mock out a super call - it feels to me like the behaviour there is part of the behaviour of the class itself, rather than the behaviour of a dependency. Mocking always feels like it should be to do with dependencies more than anything else.

Do you have a good example of the kind of call you want to mock out? If you want to mock out a call like this, would it be worth considering composition instead of inheritance?

Answer 4

There are several tests that do just that (ie specify an expected invocation on a super-class method) using the JMockit Expectations API, in the Animated Transitions sample test suite. For example, the FadeInTest test case.

Answer 5

No, there is no way of mocking super class methods with jMock.

However there is a quick-and-dirty solution to your problem. Suppose you have class A and class B extends A. You want to mock method A.a() on B. You can introduce class C extends B in your test code and override the method C.a() (just call super, or return null, id does not matter). After that mock C and use the mock everywhere, where you'd use B.

Answer 6

intercepting a super call is much too fine-grained. Don't overdo the isolation.