Mocking a parameterized constructor using powermockito

Question

Consider the code given below:

@Override
public void A()  {
    objectA = objectB.B();
    objectA.C(someValue);
        objectC = new constructor(objectA,callback());
        //Rest of the code
    }

}
public Callback callback() {
    return new callback() {
        @Override
        public void someMethod(someArgument) {
            //some Code         
       }
    };
}

I am trying to write a unit test case where:

• the call objectB.B() has to be mocked
• the call to the constructor has to be mocked

This is what I have done using Mockito and Powermockito:

@InjectMocks
ClassBeingTested testObject;

@Mock
ClassB objectB;  

@Mock
ClassC objectC;    

@Before()
public void setup()  {
    when(objectB.B()).thenReturn(new ObjectA("someValue"));

    whenNew(objectC.class).withArguments(any(),any()).thenReturn(objectC);

}
@Test()
public void testMethod() {
    testObject.A();

}

The first mock successfully works but the second mock using whenNew fails with the following error:

org.powermock.reflect.exceptions.ConstructorNotFoundException: No constructor found in class 'ClassC' with parameter types: [ null ]

If I use withArguments(objectA, callback()) where I have the implementation of callback in my test class, the actual constructor is called.

I want to mock the constructor call and restrict the call to the actual constructor. How can I do that?

I can not edit the code design since that is out of my scope.

Answer 1

In short, you get the error due to usage of 2 generic any() matchers.

When you use .withArguments(...) and set both as any() it implies .withArguments(null, null) (since any() may match pretty much anything including nulls) which folds eventually as a single null and reflection api (which PowerMock heavily relies on) fails to discover a suitable constructor for ClassC(null).

You may check out the source of org.powermock.api.mockito.internal.expectation.AbstractConstructorExpectationSetup<T> source that does the job

To fix up the issue consider using either .withAnyArguments() if you do not care of param types and stubbing all available constructors OR specify more concrete types while using any() like so whenNew(ClassC.class).withArguments(any(ClassA.class), any(Callback.class))