Major difference between: Mockito and JMockIt

Question

This is what I found from my initial attempts to use JMockIt. I must admit that I found the JMockIt documentation very terse for what it provides and hence I might have missed something. Nonetheless, this is what I understood:

Mockito: List a = mock(ArrayList.class) does not stub out all methods
of List.class by default. a.add("foo") is going to do the usual thing
of adding the element to the list.

JMockIt: @Mocked ArrayList<String> a;
It stubs out all the methods of a by default. So, now a.add("foo")
is not going to work.

This seems like a very big limitation to me in JMockIt.
How do I express the fact that I only want you to give me statistics
of add() method and not replace the function implementation itself
What if I just want JMockIt to count the number of times method  add()
was called, but leave the implementation of add() as is?

I a unable to express this in JMockIt. However, it seems I can do this
in Mockito using spy()

I really want to be proven wrong here. JMockit claims that it can do everything that other mocking frameworks do plus a lot more. Does not seem like the case here

@Test
public void shouldPersistRecalculatedArticle()
{
  Article articleOne = new Article();
  Article articleTwo = new Article();

  when(mockCalculator.countNumberOfRelatedArticles(articleOne)).thenReturn(1);
  when(mockCalculator.countNumberOfRelatedArticles(articleTwo)).thenReturn(12);
  when(mockDatabase.getArticlesFor("Guardian")).thenReturn(asList(articleOne, articleTwo));

  articleManager.updateRelatedArticlesCounters("Guardian");

  InOrder inOrder = inOrder(mockDatabase, mockCalculator);
  inOrder.verify(mockCalculator).countNumberOfRelatedArticles(isA(Article.class));
  inOrder.verify(mockDatabase, times(2)).save((Article) notNull());
}



@Test
public void shouldPersistRecalculatedArticle()
{
  final Article articleOne = new Article();
  final Article articleTwo = new Article();

  new Expectations() {{
     mockCalculator.countNumberOfRelatedArticles(articleOne); result = 1;
     mockCalculator.countNumberOfRelatedArticles(articleTwo); result = 12;
     mockDatabase.getArticlesFor("Guardian"); result = asList(articleOne, articleTwo);
  }};

  articleManager.updateRelatedArticlesCounters("Guardian");

  new VerificationsInOrder(2) {{
     mockCalculator.countNumberOfRelatedArticles(withInstanceOf(Article.class));
     mockDatabase.save((Article) withNotNull());
  }};
}

A statement like this

inOrder.verify(mockDatabase, times(2)).save((Article) notNull());

in Mockito, does not have an equivalent in JMockIt as you can see from the example above

new NonStrictExpectations(Foo.class, Bar.class, zooObj)
{
    {
        // don't call zooObj.method1() here
        // Otherwise it will get stubbed out
    }
};


new Verifications()
{
    {
        zooObj.method1(); times = N;
    }
};

Answer 1

In fact, all mocking APIs mock or stub out every method in the mocked type, by default. I think you confused mock(type) ("full" mocking) with spy(obj) (partial mocking).

JMockit does all that, with a simple API in every case. It's all described, with examples, in the JMockit Tutorial. For proof, you can see the sample test suites (there are many more that have been removed from newer releases of the toolkit, but can still be found in the old zip files), or the many JMockit integration tests (over one thousand currently).

The equivalent to Mockito's spy is "dynamic partial mocking" in JMockit. Simply pass the instances you want to partially mock as arguments to the Expectations constructor. If no expectations are recorded, the real code will be executed when the code under test is exercised. BTW, Mockito has a serious problem here (which JMockit doesn't), because it always executes the real code, even when it's called inside when(...) or verify(...); because of this, people have to use doReturn(...).when(...) to avoid surprises on spied objects.

Regarding verification of invocations, the JMockit Verifications API is considerably more capable than any other. For example:

new VerificationsInOrder() {{
    // preceding invocations, if any
    mockDatabase.save((Article) withNotNull()); times = 2;
    // later invocations, if any
}};

Answer 2

Mockito's a much older library than JMockIT, so you could expect that it would have many more features. Have a read through the release list if you want to see some of the less well documented functionality. JMockIT authors have produced a matrix of features in which they missed out every single thing that other frameworks do that they don't, and got several wrong (for instance, Mockito can do strict mocks and ordering).

Mockito was also written to enable unit-level BDD. That generally means that if your tests provide a good example of how to use the code, and if your code is lovely and decoupled and well-designed, then you won't need all the shenanigans that JMockIT provides. One of the hardest things to do in Open Source is say "no" to the many requests that don't help in the long run.

Compare the examples on the front pages of Mockito and JMockIT to see the real difference. It's not about what you test, it's about how well your tests document and describe the behavior of the class.

Declaration of Interest: Szczepan and I were on the same project when he wrote the first draft of Mockito, after seeing some of us roll out our own stub classes rather than use the existing mocking frameworks of the time. So I feel like he wrote it all for me, and am thoroughly biased. Thank you Szczepan.