Verify method invocation without executing its actual implementation on a Spy

Question

Let's assume the following test

public void someTest() throws Exception {
   Foo foo = spy(new Foo());
   foo.someMethod(); // invokes methodToBeVerified()
   verify(foo).methodToBeVerified();
}

When the test executes it calls the actual implementation of foo.methodToBeVerified(). I would like the test to verify whether that particular method has been called or not but I do not want its implementation to be to executed. Is it possible to do that using Mockito's Spy?

Answer 1

Yes, using

doNothing().when(foo).methodToBeVerified();

as in the following example

public class FooTest {

    static class Foo {

        public void someMethod() {
            System.out.println("someMethod called");
            System.out.println("calling method to be verified...");
            methodToBeVerified();
        }

        public void methodToBeVerified() {
            System.out.println("methodToBeVerified called");
        }
    }

    @Test
    public void someTest() throws Exception {
        Foo foo = spy(new Foo());
        doNothing().when(foo).methodToBeVerified();
        foo.someMethod();
        verify(foo).methodToBeVerified();
    }

}

---

For reference, what you are looking for is called Partial Mocks. Real (spied) partial mocks are supported in Mockito since 1.8.0.