What is the difference between unit testing and integration testing in Spring Boot? स्प्रिंग बूट में यूनिट टेस्टिंग और इंटीग्रेशन टेस्टिंग में क्या अंतर है?

Unit testing verifies a single class or method in complete isolation, with all its dependencies replaced by mocks (using Mockito), so the test runs fast and doesn't load any Spring context. Integration testing verifies how multiple components work together — controller, service, repository, and sometimes a real or embedded database — by loading part or all of the Spring application context.

A healthy test suite favors many fast unit tests for business logic and a smaller number of integration tests for critical end-to-end flows, since integration tests are slower (due to context startup) and more brittle to unrelated changes. Spring Boot supports both: plain JUnit + Mockito for unit tests, and annotations like @SpringBootTest for full-context integration tests.

// Unit test — no Spring context
@ExtendWith(MockitoExtension.class)
class OrderServiceTest {
    @Mock private PaymentGateway paymentGateway;
    @InjectMocks private OrderService orderService;
}

// Integration test — loads full Spring context
@SpringBootTest
class OrderIntegrationTest { ... }