How to mock super class method using Mockito or any other relevant java framework

Question

My Scenario is as below

class SuperClass{
   public void run(){
      System.out.println("I am running in Super class");
   }
}

class ChildClass extends SuperClass{
  public void childRunner(){
     System.out.println("Step 1");
     System.out.println("Step 2");
     **run();**
     System.out.println("Last Step");
  }
}

Now I want to test the childRunner() method of ChildClass and since this method internally calls the super class method, i need some help/piece of code on how to mock the run() method which is present in SuperClass.

Answer 1

Ideally, you should "favor composition over inheritance".

If you don't have this option you could use doNothing which basically tells Mockito to do nothing when a method in a mock/spy object is called. This was also discussed here

Following code example should help

@Test
public void tst() {
    ChildClass ch = Mockito.spy(new ChildClass());
    Mockito.doNothing().when((SuperClass)ch).run();
    ch.childRunner();

}

class SuperClass{
    public void run(){
        System.out.println("I am running in Super class");
    }
}

class ChildClass extends SuperClass{
    public void childRunner(){
        System.out.println("Step 1");
        run();
        System.out.println("Last Step");
    }
}

output:

Step 1
Last Step

In case you use super.run(); this won't work

Answer 2

Here is an example for a class that extends another class and it has some other dependencies. In this case, I'll move the superclass call into the other method and then mock the superclass caller method.

class Child extends Parent {

  @Autowired
  private Dependicy d;

  public Authentication authenticate(Authentication auth) {
    the code to be tested...
    superAuthenticate(auth);// the code that I don't want to deal with it.
    return auth;
  }

  protected Authentication superAuthenticate(Authentication auth) {
    return super.authenticate(auth);
  }
}

As you can see above, the authenticate method does some logic and then call the super class's method, so I want to mock the superclass call and test my own code block. Here is my test class:

@RunWith(MockitoJUnitRunner.class)
public class ChildTest {
    @Mock
    private Dependicy d;
    @InjectMocks
    private Child child = new Child();

    @Test
    public void testSomething() {
        Child spy = Mockito.spy(child);

        when(d.aMethod(aParam)).thenReturn(aResult);
        doReturn(usefulResult).when(spy).superAuthenticate(any());

        Authentication result = spy.authenticate(auth);
        assertThat(result).isNotNull;
    }
}