最终 class 和最终方法 - Mocking 和 Mockito 2

Question

Is the feature provided by Mockito 2 to mock final methods and final classes using org.mockito.plugins.MockMaker(mock-maker-inline) generally available(released) or still in the incubation phase. I am using mockito-core-2.23.4 artifact in my application. Need suggestions in mocking the final classes and methods. Is it advisable to use this approach or look for alternate options?

Answer 1

As of Mockito 2.x, Mockito now supports mocking of final classes and methods.

Example:

Say we have a MyList class shown below as the collaborator in test cases.

We'll add a new finalMethod to this class:

public class MyList extends AbstractList {
    final public int finalMethod() {
        return 0;
    }
}

And we'll also extend it with a final subclass:

public final class FinalList extends MyList {     
    @Override
    public int size() {
        return 1;
    }
}

Before Mockito can be used for mocking final classes and methods, it needs to be configured.

We need to add a text file to the project's src/test/resources/mockito-extensions directory named org.mockito.plugins.MockMaker and add a single line of text:

mock-maker-inline

Mockito checks the extensions directory for configuration files when it is loaded. This file enables the mocking of final methods and classes.

Mock a Final Method:

Once Mockito is properly configured, a final method can be mocked like any other:

@Test
public void whenMockFinalMethodMockWorks() {

    MyList myList = new MyList();

    MyList mock = mock(MyList.class);
    when(mock.finalMethod()).thenReturn(1);

    assertNotEquals(mock.finalMethod(), myList.finalMethod());
}

By creating a concrete instance and a mock instance of MyList, we can compare the values returned by both versions of finalMethod() and verify that the mock is called.

Mock a Final Class:

Mocking a final class is just as easy as mocking any other class:

@Test
public void whenMockFinalClassMockWorks() {

    FinalList finalList = new FinalList();

    FinalList mock = mock(FinalList.class);
    when(mock.size()).thenReturn(2);

    assertNotEquals(mock.size(), finalList.size());
}

Similar to the test above, we create a concrete instance and a mock instance of our final class, mock a method and verify that the mocked instance behaves differently.

Reference: https://www.baeldung.com/mockito-final