JMockit - returnsFirstArg equivalent

Question

I have to mock a method using jmockit which returns the same arguments I passed. With Mockito, I used AdditionalAnswers.returnsFirstArg:

PowerMockito.when(entityManager.merge((Request)Mockito.any())).then(AdditionalAnswers.returnsFirstArg());

How can I write this with jmockit?

new Expectations() {
        {
            entityManager.merge((Request) any);
            returns(????);
        }
    };

Answer 1

JMockit doesn't have this feature out-of-the-box, but it can be implemented easily enough, with a reusable Delegate class:

class FirstArgument implements Delegate<Object> {
    Object delegate(Invocation inv) { return inv.getInvokedArguments()[0]; }
}

@Mocked EntityManager entityManager;

@Test
public void expectationRecordedToReturnAnArgument()
{
    new Expectations() {{
        entityManager.merge(any);
        result = new FirstArgument();
    }};

    // From the code under test:
    EntityClass entity = new EntityClass();
    EntityClass merged = entityManager.merge(entity);

    assertSame(entity, merged);
}