@MockBean vs @Mock Spring Boot | Java Fresher Interview

Direct Answer

@Mock creates a standalone Mockito mock and does not add it to Spring. The older Spring Boot @MockBean replaces or adds a bean inside a test ApplicationContext; since Spring Boot 3.4 it is deprecated for removal in Boot 4.0 in favor of Spring Framework's @MockitoBean. Use @Mock for a plain unit test and a bean override when a Spring test such as @WebMvcTest needs the mock in context-managed wiring.

Code Example

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

    @Test
    void rejectsDeclinedPayment() {
        var service = new OrderService(gateway);
        when(gateway.charge(100)).thenReturn(false);

        assertThrows(PaymentDeclinedException.class,
                () -> service.placeOrder(100));
    }
}

// Spring MVC slice: mock is registered in the test context
@WebMvcTest(OrderController.class)
class OrderControllerTest {
    @Autowired MockMvc mvc;
    @MockitoBean OrderService service;
}

Common Mistakes & Pitfalls

• Using the wrong lifecycle: @Mock needs Mockito initialization; a Spring bean override needs a Spring TestContext.
• Confusing context loading with mocking: @MockBean does not by itself turn a plain unit test into a Spring test.
• Unnecessary context tests: if new OrderService(mockGateway) is enough, a plain Mockito test is clearer.
• Ignoring current APIs: on current Spring versions, prefer @MockitoBean; @MockBean is the older Boot annotation.
• Fragmenting the context cache: inconsistent override declarations across test classes can reduce reuse of cached contexts.