1. Overview
In this short tutorial, we’ll focus on how to mock final classes and methods using Mockito.
As with other articles focused on the Mockito framework (such as Mockito Verify, Mockito When/Then and Mockito’s Mock Methods), we’ll use the MyList class shown below as the collaborator in test cases.
We’ll add a new method for this tutorial:
public class MyList extends AbstractList<String> {
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;
}
}
2. Mock a Final Method
Once we’ve properly configured Mockito, we can mock a final method like any other:
@Test
public void whenMockFinalMethod_thenMockWorks() {
MyList myList = new MyList();
MyList mock = mock(MyList.class);
when(mock.finalMethod()).thenReturn(1);
assertThat(mock.finalMethod()).isNotZero();
}
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.
3. Mock a Final Class
Mocking a final class is just as easy as mocking any other class:
@Test
public void whenMockFinalClass_thenMockWorks() {
FinalList mock = mock(FinalList.class);
when(mock.size()).thenReturn(2);
assertThat(mock.size()).isNotEqualTo(1);
}
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.
4. Conclusion
In this quick article, we covered how to mock final classes and methods with Mockito by using a Mockito extension.
The full examples, as always, can be found on GitHub.
