What is the best way to mock void methods using Mockito?

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What is the best way to mock void methods using Mockito?

I am trying to mock methods that return void, but I am unsure how to do it with mockito void method.

I implemented an observer pattern, but I can’t seem to mock it correctly using Mockito. I searched for examples but didn’t find a clear solution.

Here’s my class structure:

public class World {

    List<Listener> listeners;

    void addListener(Listener item) {
        listeners.add(item);
    }

    void doAction(Action goal, Object obj) {
        setState("i received");
        goal.doAction(obj);
        setState("i finished");
    }

    private String state;
    // Setter and getter for state
}

public class WorldTest implements Listener {

    @Test
    public void testWorld() {
        World w = mock(World.class);
        w.addListener(this);
        // Test logic here
    }
}

interface Listener {
    void doAction();
}

The system does not trigger properly with mock objects. I want to observe the system state and make assertions based on those states. What is the right approach for mocking void methods in Mockito?