Using Mockito's ArgumentCaptor class to match a child class

Question

The below code shows my problem. Effectively, I am trying to use Mockito's ArgumentCaptor to verify that a method was called once with a certain concrete class. I would like to use ArgumentCaptor here if possible, but I am beginning to suspect I need to use a custom ArgumentMatcher instead.

The problem is that the line Mockito.verify(mocked).receive(captor.capture()); (Edit: Added this to the code below) fails with a TooManyActualInvocations exception (2 instead of 1). I would like to understand why this is happening - is it poor implementation of Mockito or a limitation caused by type erasure of generics?

public class FooReceiver {
  public void receive(Foo foo) {

  }
}

public interface Foo {
}

public class A implements Foo {
}

public class B implements Foo {
}

public class TestedClass {
  private FooReceiver receiver;
  public TestedClass(FooReceiver receiver) {
    this.receiver = receiver;
  }

  public void doStuff() {
    receiver.receive(new A());
    receiver.receive(new B());
  }
}

public class MyTest {

  @Test
  public void testingStuff() {
    // Setup
    FooReceiver mocked = Mockito.mock(FooReceiver.class);
    TestedClass t = new TestedClass(mocked);

    // Method under test
    t.doStuff();

    // Verify
    ArgumentCaptor<B> captor = ArgumentCaptor.forClass(B.class);
    Mockito.verify(mocked).receive(captor.capture()); // Fails here

    Assert.assertTrue("What happened?", captor.getValue() instanceof B);
  }
}

EDIT: For anyone interested, I ended up doing this:

// Verify
final B[] b = new B[1];
ArgumentMatcher<B> filter = new ArgumentMatcher<B>() {
  @Override
  public boolean matches(Object argument) {
    if(argument instanceof B) {
      b[0] = (B) argument;
      return true;
    }
    return false;
  }
}
Mockito.verify(mocked).receive(Mockito.argThat(filter));

Answer 1

You can also use Mockito.isA to verify that the argument is of a specific class:

verify(mock).init(isA(ExpectedClass.class));

Mockito JavaDoc

Answer 2

As far as I can tell this is a limitation / poor implementation. When looking at org.mockito.internal.matchers.CapturingMatcher there is

public boolean matches(Object argument) {
    return true;
}

meaning it matches every argument / class.

This results in org.mockito.internal.matchers.CapturingMatcher#getAllValues returning a List<B> but actually containing one A and one B resulting in a ClassCastException during runtime when trying to get them as B.

List<Object> arguments; // the invocations

// adds a new invocation
public void captureFrom(Object argument) {
    // ... 
    this.arguments.add(argument);
    // ... 
}

// return the list of arguments, using raw types remove any compiler checks for validity,
// the returned List contains elements that are not of type T
public List<T> getAllValues() {
    // ... 
    return new ArrayList<T>((List) arguments);
    // ... 
}

This should be solvable by changing org.mockito.ArgumentCaptor in a way that it passes its Class<? extends T> clazz into the CapturingMatcher and therefore passing the type information along properly, enabling a proper matches implementation and removing the need for the cast / raw type usage.