MockitoExtension

MockitoExtension is a JUnit 5 extension that integrates the Mockito mocking framework with the Jupiter test platform. It provides automatic mock initialization and supports injection of mocks into the class under test, reducing boilerplate in test setup. The extension is part of the Mockito library and is located in the org.mockito.junit.jupiter package.

Usage typically involves annotating a test class with @ExtendWith(MockitoExtension.class) and marking fields with Mockito annotations such as @Mock, @Spy, @Captor, and @InjectMocks. When a test runs, the extension creates mock instances for the annotated fields and injects them into the object under test, using constructor, setter, or field injection as available. The extension also enables optional parameter injection, allowing test methods to declare parameters that are resolved as mocks by the framework.

MockitoExtension supports several features aimed at improving test reliability, including strict stubbing by default, which helps detect unused or unnecessary interactions. This behavior can be adjusted with configuration, such as @MockitoSettings(strictness = Strictness.LENIENT). The extension ensures mocks are reset between tests and can also provide mocks as parameters to test methods, simplifying test signatures.

Compared with JUnit 4 approaches like MockitoJUnitRunner or MockitoAnnotations, MockitoExtension offers native support for JUnit 5 and a more modular, extensible approach to mock management. It is commonly used to streamline test setup, improve readability, and align Mockito usage with modern JUnit 5 testing practices.