[FIXED] Mocking function in the same class java

Issue

I am writing unit tests for a class, and I need to mock a call to a method in the same class.

//My class:
public class Class {
   public void functionA(arguments){
      ...
      String s3 = functionB(s1, s2);
   }

   public String functionB(String s1, String s2){
     ...
     return s3;
   }
}



//My Test:
@Test
public void functionA_Test(){
   Class class = new Class(dependency);
   Class spyClass = spy(class);

   mockString = "this is a mock";
   when(spyClass.functionB(any(),any()).thenReturn(mockString);

   spyClass.functionA(arguments);
}

When I debug the test function, after reaching when(spyClass.functionB(any(),any()).thenReturn(mockString);, the program jumps to the main class, inside functionB, to run it. What I want is to automatically assign s3=mockString when calling functionB from functionA.

Solution

When calling when(spyClass.functionB(any(),any()).thenReturn(mockString), it will indeed go through the real method in debug mode. But the method is mocked, and your functionA gets the mockString. It does work. I don't really understand why seing that you can go into debug mode into it is a problem.

To answer the question, using mock won't go through the method:

Class mockClass = mock(Class.class);

when(mockClass.functionB(any(),any())).thenReturn(mockString);
when(mockClass.functionA(arguments)).thenCallRealMethod();

mockClass.functionA(arguments);

BUT : this is a really bad test, you should never need to do that (spy or mock). If you test a class, then you test all of it. If you need to mock a method to test another one, one of them probably belongs to another class.

Answered By - Anne
Answer Checked By - Timothy Miller (JavaFixing Admin)