How to mock void methods with Mockito

Take a look at the Mockito API docs. As the linked document mentions (Point # 12) you can use any of the doThrow(),doAnswer(),doNothing(),doReturn() family of methods from Mockito framework to mock void methods.

For example,

Mockito.doThrow(new Exception()).when(instance).methodName();

or if you want to combine it with follow-up behavior,

Mockito.doThrow(new Exception()).doNothing().when(instance).methodName();

Presuming that you are looking at mocking the setter setState(String s) in the class World below is the code uses doAnswer method to mock the setState.

World mockWorld = mock(World.class); 
doAnswer(new Answer<Void>() {
    public Void answer(InvocationOnMock invocation) {
      Object[] args = invocation.getArguments();
      System.out.println("called with arguments: " + Arrays.toString(args));
      return null;
    }
}).when(mockWorld).setState(anyString());

I think I've found a simpler answer to that question, to call the real method for just one method (even if it has a void return) you can do this:

Mockito.doCallRealMethod().when(<objectInstance>).<method>();
<objectInstance>.<method>();

Or, you could call the real method for all methods of that class, doing this:

<Object> <objectInstance> = mock(<Object>.class, Mockito.CALLS_REAL_METHODS);