Mockito.any returns null

Question

I am trying to mock a static method with parameters like this :

Mockito.when(StaticClass.staticMethod(Mockito.any(A.class), 
                                      Mockito.any(B.class), SomeEnum.FOO))
       .thenReturn(true);

I have added the following annotations :

@RunWith(PowerMockRunner.class)
@PowerMockRunnerDelegate(Parameterized.class)
@PrepareForTest({StaticClass.class, A.class, B.class})

But Mockito.any always returns null. Why ?

Answer 1

Short answer: Use doReturn().when() instead of when().then()

Long answer can be found over here: How do Mockito matchers work?

Matchers return dummy values such as zero, empty collections, or null. Mockito tries to return a safe, appropriate dummy value, like 0 for anyInt() or any(Integer.class) or an empty List for anyListOf(String.class). Because of type erasure, though, Mockito lacks type information to return any value but null for any()

NullPointerException or other exceptions: Calls to when(foo.bar(any())).thenReturn(baz) will actually call foo.bar(null), which you might have stubbed to throw an exception when receiving a null argument. Switching to doReturn(baz).when(foo).bar(any()) skips the stubbed behavior.

Side Note: This issue could also be described something like, How to use Mockito matchers on methods that have precondition checks for null parameters?