How Can Mockito Simplify Testing Abstract Classes?

Mocking Abstract Classes with Mockito

Testing abstract classes can pose challenges, especially if manual mock creation is considered. However, leveraging Mockito offers an alternative approach.

Mockito.mock() with Answers.CALLS_REAL_METHODS

Instead of manually constructing a mock class, Mockito's mock() method can be utilized with the Answers.CALLS_REAL_METHODS argument. This option generates a mock class that inherits from the abstract class and enables the testing of real methods without explicitly implementing them.

Example:

Consider an abstract class My with a method under test methodUnderTest() and an abstract method methodIDontCareAbout(). The following code snippet demonstrates how to test methodUnderTest() using this approach:

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

In this example, Mockito.mock(My.class, Answers.CALLS_REAL_METHODS) creates a mock instance of My that allows the real implementation of methodUnderTest() to run, enabling the testing of its logic. Simultaneously, the abstract method methodIDontCareAbout() doesn't need to be implemented, as it isn't invoked by the test.

Benefits

This approach streamlines the testing of abstract classes by eliminating the need to create custom subclasses or implement abstract methods. It also maintains the desired separation between the abstract class and the test case, allowing for cleaner and more concise tests.

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