How to make mock to void methods with mockito

Question

I implemented an Observer pattern but I can't mock it with Mockito because I don't know how.

And I tried to find an example on the Internet, but didn't succeed.

My class looks like

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 getter state
} 

public class WorldTest implements Listener {

    @Test public void word{
    World  w= mock(World.class);
    w.addListener(this);
    ...
    ...

    }
}

interface Listener {
    void doAction();
}

The system are not triggered with mock. =( I want to show above mentioned system state. And make assertion according to them.

Answer 1

ake 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());

Answer 2

Try this:

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

Answer 3

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

This is the best way to use mock to your mockito. It worked fine for me. Hope this helps.

Answer 4

Read this article for better understanding of mockito

https://static.javadoc.io/org.mockito/mockito-core/2.23.4/org/mockito/Mockito.html

Answer 5

import static org.mockito.Mockito.*;

mockito offers "Spy" for using partial mock function.

You can use it as follows:

private World world = spy(World.class);

To eliminate a method from being executed you could use something like this:

doNothing().when(someObject).someMethod(anyObject());

to give some custom behaviour to a method use "when" with an "thenReturn":

doReturn("something").when(this.world).someMethod(anyObject());

Answer 6

https://examples.javacodegeeks.com/core-java/mockito/mockito-mock-void-method-call/

Here you can find the ways it can be done.

Answer 7

public class Test {
    @Mock
    private test1 t1;
    @InjectMocks
    private Test service;
    @Before
    public void setUp() throws Exception {
         MockitoAnnotations.initMocks(this);
    }
    @Test
    public void trythis() {
         //assertion here
    }
}

This way you can use mock using mockito

Answer 8

This article can give the idea on what is mock and how to use it using mockito

https://www.journaldev.com/21834/mockito-mock-void-method

Answer 9

You can use partial mocking to serve the purpose also

Mockito’s doCallRealMethod() can be used for void methods.