Mockito Setup in Spring Boot

Direct Answer

Mockito creates configurable test doubles for Java. A Spring Boot project that declares spring-boot-starter-test normally receives Mockito and its JUnit Jupiter support through that test dependency. For a plain JUnit 5 unit test, use @ExtendWith(MockitoExtension.class) or create mocks with Mockito.mock. Add a direct Mockito dependency only when the project does not use the Boot test starter or needs an explicitly managed setup.

Code Example

<!-- Maven: the declared Boot test starter supplies Mockito support -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-test</artifactId>
    <scope>test</scope>
</dependency>

// Plain unit test: no Spring context
@ExtendWith(MockitoExtension.class)
class OrderServiceTest {
    @Mock OrderRepository repository;

    @Test
    void findsAnOrder() {
        var service = new OrderService(repository);
        when(repository.findById(7L)).thenReturn(Optional.of(new Order(7L)));

        assertEquals(7L, service.find(7L).id());
    }
}

// Context test: current Spring bean override
@WebMvcTest(OrderController.class)
class OrderControllerTest {
    @MockitoBean OrderService service;
}

Common Mistakes & Pitfalls

• Assuming the starter exists: confirm it in the build file.
• Adding competing versions: let Spring Boot manage versions unless the project has a deliberate override.
• Forgetting Mockito initialization: @Mock fields need the extension, runner, or openMocks lifecycle.
• Confusing unit and context tests: a plain Mockito test does not need @SpringBootTest.
• Using a legacy bean override in new code: current Spring uses @MockitoBean; Boot's @MockBean is deprecated since 3.4.