How Can Mockito Help You Test Abstract Classes Without Explicit Subclassing?

Mockito and Testing Abstract Classes

Testing abstract classes can pose challenges. Manually hand-crafting mocks through inheritance feels cumbersome and redundant. Fortunately, mocking frameworks like Mockito offer alternative approaches.

Mockito's ASSIST WITH MOCKING ABSTRACT CLASSES

Mockito enables seamless mocking of abstract classes while bypassing the need for explicit subclassing. By utilizing Mockito.mock(My.class, Answers.CALLS_REAL_METHODS), you can create a mock that inherits from the abstract class. This mock acts as both a subclass and a partial mock.

AVOIDING ABSTRACT METHOD IMPLEMENTATION

The Answers.CALLS_REAL_METHODS configuration allows you to mock abstract methods without implementing them. The real methods will be executed as-is, unless explicitly stubbed out in your test.

EXAMPLE IMPLEMENTATION

Consider the following abstract class and a test case:

<code class="java">public abstract class My {
  public Result methodUnderTest() { ... }
  protected abstract void methodIDontCareAbout();
}
 
public class MyTest {
    @Test
    public void shouldFailOnNullIdentifiers() {
        My my = Mockito.mock(My.class, Answers.CALLS_REAL_METHODS);
        Assert.assertSomething(my.methodUnderTest());
    }
}</code>

In this example, the mock is created using Mockito.mock(), and Answers.CALLS_REAL_METHODS ensures that the method methodUnderTest() is run as defined in the abstract class, even though methodIDontCareAbout() is not implemented. This approach simplifies the testing process and eliminates the need for manual subclass creation.

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