How to mock a method of the same class?

Question

In the testing method, there are methods of the same class. How to mock the methods of the same class?

An example is as follows.

I am testing method2. It involves method1 which is in the same class. How to mock this method1?

public class A
{
  public void method1(int a, int b){

  }

  public void method2(){

      int value = method1(10,20);
  }
}

Answer 1

You can use a Spy to do this, in combination with doReturn to stub out the method for which you want to provide canned behavior. There are many examples available on how to use a spy. Check out these tutorials and documentation:

• Mockito: mocking a method of same class called by method under test when using @InjectMocks
• https://www.baeldung.com/mockito-spy
• Mockito: Trying to spy on method is calling the original method

Example:

   List list = new LinkedList();
   List spy = spy(list);

   //Use doReturn to change the behavior of a method call
   doReturn("foo").when(spy).get(0);