Mocking a call on a public method of an abstract class without subclassing the abstract Class, using mockito prefererably

Question

I am writing an unit testing using JUNIT + Mockito to test a method like :

public someObject methodUnderTest(){
  SomeObject obj = SomeAbstractClass.someMethod();

  if(obj!=null){
    obj.someOtherMethod();
  }

  return someThing;
}

And I would like to mock the call on abstract Class "SomeAbstractClass" mentioned in above code fragment so i can verify call on "obj" like :

verify(SomeAbstractClass).someMethod();
verify(obj).someOtherMethod();

I have tried using mockito features like : Mockito.CALLS_REAL_METHODS Mockito.RETURNS_MOCKS

but they don't work due to dependencies not available to the SomeAbstractClass.

Note:

1) SomeObject is an Interface.

2) I need a technique to test above code fragment. I am constrained to use the above code fragment and cannot change the code fragment.

Answer 1

You can use PowerMock to mock static and final methods.

Answer 2

It sounds like the problem is that your use of CALLS_REAL_METHODS is applying to the entire class, where you really want to mock out specific methods (i.e. make a "partial mock"). You have two options here, one using thenCallRealMethod, and one using CALLS_REAL_METHODS and then specifically mocking the calls you need:

public void testMethodUnderTest_mockSpecificThings() {
    SomeAbstractClass myAbstractClass = Mockito.mock(SomeAbstractClass.class);
    SomeAbstractClass myObject = Mockito.mock(SomeObject.class);
    when(myAbstractClass.someMethod()).thenReturn(foo);
    when(myAbstractClass.methodUnderTest()).thenCallRealMethod();

    myAbstractClass.methodUnderTest();

    verify(myAbstractClass).someMethod();
    verify(myObject).someOtherMethod();
}

public void testMethodUnderTest_makeSpecificRealCalls() {
    SomeAbstractClass myAbstractClass =
        Mockito.mock(SomeAbstractClass.class, CALLS_REAL_METHODS);
    SomeAbstractClass myObject = Mockito.mock(SomeObject.class);
    // overrides the default answer
    when(myAbstractClass.someMethod()).thenReturn(myObject);

    myAbstractClass.methodUnderTest();

    verify(myAbstractClass).someMethod();
    verify(myObject).someOtherMethod();
}

Be forewarned that SomeAbstractClass is never actually instantiated, so if you rely on any behavior in the abstract class constructor, like variable initialization--including inline initialization where the fields are declared--you will need to make those calls explicitly yourself.

Answer 3

Assumption: if you write unit test, I guess you still can modify tested method a bit.

Solution:

1. extract static method call to overridable method:

public someObject methodUnderTest() {
    SomeObject obj = getSomeObject();

    if(obj!=null){
      obj.someOtherMethod();
    }

    return someThing;
}

protected SomeObject getSomeObject() {
    return SomeAbstractClass.someMethod();
}

1. then you can use Mockito Spy to partially mock the object you actually test:

private ClassUnderTest classUnderTest;

@Before
public void setUp() {
    classUnderTest= new ClassUnderTest();
    classUnderTest = Mockito.spy(classUnderTest);
}

@Test
public void test() {
    SomeObject someObject = Mockito.mock(SomeObject.class);
    when(classUnderTest.getSomeObject()).thenReturn(someObject);
    classUnderTest.methodUnderTest();
    verify(someObject).someOtherMethod();
}

@Test
public void testNull() {
    when(classUnderTest.getSomeObject()).thenReturn(null);
    classUnderTest.methodUnderTest();
    verify(something);
}

Answer 4

Use anonymous classes:

public interface SomeObject {
     public Object someOtherMethod();
}

public abstract class SomeAbstractClass {
    abstract SomeObject someMethod();
}

@Test
public void test() {
    SomeAbstractClass target = new SomeAbstractClass() {
        SomeObject someMethod() {
            // some impl
            SomeObject someObject = new SomeObject() {
                public Object someOtherMethod() {
                    // some other impl
                }
            };
            return someObject;
        }
    };

    // now test target
}