Testing GWTP presenter with asynchronous calls

Question

I'm using GWTP, adding a Contract layer to abstract the knowledge between Presenter and View, and I'm pretty satisfied of the result with GWTP. I'm testing my presenters with Mockito.

But as time passed, I found it was hard to maintain a clean presenter with its tests. There are some refactoring stuff I did to improve that, but I was still not satisfied.

I found the following to be the heart of the matter : My presenters need often asynchronous call, or generally call to objects method with a callback to continue my presenter flow (they are usually nested).

For example :

  this.populationManager.populate(new PopulationCallback()
  {
     public void onPopulate()
     {
        doSomeStufWithTheView(populationManager.get());
     }
  });

In my tests, I ended to verify the population() call of the mocked PopulationManager object. Then to create another test on the doSomeStufWithTheView() method.

But I discovered rather quickly that it was bad design : any change or refactoring ended to broke a lot of my tests, and forced me to create from start others, even though the presenter functionality did not change ! Plus I didn't test if the callback was effectively what I wanted.

So I tried to use mockito doAnswer method to do not break my presenter testing flow :

doAnswer(new Answer(){
     public Object answer(InvocationOnMock invocation) throws Throwable
     {
        Object[] args = invocation.getArguments();
        ((PopulationCallback)args[0]).onPopulate();
        return null;
     }
 }).when(this.populationManager).populate(any(PopulationCallback.class));

I factored the code for it to be less verbose (and internally less dependant to the arg position) :

doAnswer(new PopulationCallbackAnswer())
  .when(this.populationManager).populate(any(PopulationCallback.class));

So while mocking the populationManager, I could still test the flow of my presenter, basically like that :

@Test
public void testSomeStuffAppends()
{
  // Given
  doAnswer(new PopulationCallbackAnswer())
  .when(this.populationManager).populate(any(PopulationCallback.class));

  // When
  this.myPresenter.onReset();

  // Then
  verify(populationManager).populate(any(PopulationCallback.class)); // That was before
  verify(this.myView).displaySomething(); // Now I can do that.
}

I am wondering if it is a good use of the doAnswer method, or if it is a code smell, and a better design can be used ?

Usually, my presenters tend to just use others object (like some Mediator Pattern) and interact with the view. I have some presenter with several hundred (~400) lines of code.

Again, is it a proof of bad design, or is it normal for a presenter to be verbose (because its using others objects) ?

Does anyone heard of some project which uses GWTP and tests its presenter cleanly ?

I hope I explained in a comprehensive way.

Thank you in advance.

PS : I'm pretty new to Stack Overflow, plus my English is still lacking, if my question needs something to be improved, please tell me.

Answer 1

You could use ArgumentCaptor:
Check out this blog post fore more details.