using ArgumentCaptor<List> and hamcrest.hasSize

Question

I'm using Mockito and Hamcrest for unittesting in Java.

Very often I use Hamcrests hasSize to assert some collection has a certain size. A few minutes ago, I was writing a test where I'm capturing a List of the invocation of (replaced the names):

public void someMethod(A someObject, List<B> list)

The test:

@Test
public void test() {
    // (...)
    ArgumentCaptor<List> captor = ArgumentCaptor.forClass(List.class);
    verify(someMock).someMethod(same(otherObject), captor.capture());
    assertThat(captor.getValue().size(), is(2)); // This works
    assertThat(captor.getValue(), hasSize(2)); // This gives a compile error
    // TODO more asserts on the list
}

Question: The test runs green with the first assertThat, and there's probably other ways to solve this too (for example, implementing ArgumentMatcher<List>), but because I always use hasSize, I'd like to know how I can fix this compile error:

The method assertThat(T, Matcher<? super T>) in the type MatcherAssert is not applicable for the arguments (List, Matcher<Collection<? extends Object>>)

Answer 1

One way to workaround this problem is by defining your captor using mockito annotations, like:

@RunWith(MockitoJUnitRunner.class)
public class MyTestClass {

    @Captor
    private ArgumentCaptor<List<B>> captor; //No initialisation here, will be initialized automatically

    @Test
    public testMethod() {
        //Testing...
        verify(someMock).someMethod(same(otherObject), captor.capture());
        assertThat(captor.getValue(), hasSize(2));
    }
}