Spring Boot Testing Spring Applications Questions and Answers

Question 1

A developer needs to write a test for a Spring MVC `@RestController` that focuses exclusively on the web layer. The test should verify request mappings, JSON serialization/deserialization, and exception handling without loading the service or repository layers. Which annotation is most suitable for this purpose?

Accepted Answer

`@WebMvcTest(MyController.class)`

Answer

`@WebMvcTest` is a test slice annotation that sets up an application context containing only the beans necessary for testing the web layer, such as controllers, filters, and MVC infrastructure. [7, 11, 12] It does not load `@Service` or `@Repository` beans, making it lightweight and fast for focused controller testing. [7, 18] `@SpringBootTest` loads the entire application context, `@DataJpaTest` focuses on the persistence layer, and `@ExtendWith(MockitoExtension.class)` is a general JUnit 5 extension for Mockito, not specific to Spring's web layer testing.

Question 2

In a Spring Boot integration test annotated with `@SpringBootTest`, what is the primary function of the `@MockBean` annotation?

Accepted Answer

To add a new bean or replace an existing bean in the `ApplicationContext` with a Mockito mock.

Answer

The `@MockBean` annotation is used in Spring Boot tests to add a Mockito mock to the `ApplicationContext`. [1] If a bean of the same type already exists, it will be replaced by the mock. This allows you to simulate the behavior of a dependency (like a service or repository) within a full or sliced application context test, isolating the component under test from its actual dependencies. [8, 16] The mock is automatically reset after each test method. [1]

Question 3

When writing a test class annotated with `@DataJpaTest`, which of the following behaviors is NOT part of its default configuration?

Accepted Answer

Loading the full application context, including web controllers and services.

Answer

`@DataJpaTest` is a test slice annotation focused on testing the persistence layer. By default, it disables full auto-configuration and only loads JPA-related components like repositories and entities. [5, 9, 13] It also configures an in-memory database and makes tests transactional with automatic rollback. [4, 15] It specifically does NOT load other beans like `@Controller` or `@Service` to keep the tests fast and focused on data access logic. [5]

Question 4

A developer needs to write a full integration test for a REST API. The test must start the application on an actual (but random) port and make real HTTP requests to the endpoints to verify the complete request-response cycle. Which annotation and helper class combination is best suited for this scenario?

Accepted Answer

`@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)` and `TestRestTemplate`

Answer

To perform a full-stack integration test with a running server, `@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)` is used. This starts the embedded server on a random port. [6, 17, 20] The `TestRestTemplate` is a utility provided by Spring Boot specifically for making live HTTP calls to the running application in such integration tests. [2, 20] In contrast, `MockMvc` operates on a mocked servlet environment without a real server. [2, 14]

Question 5

An integration test requires a database connection whose JDBC URL is determined at runtime by a Testcontainers-managed Docker container. Which annotation should be used on a static method within the test class to add this dynamically generated URL to the Spring `Environment` before the context is refreshed?

Accepted Answer

`@DynamicPropertySource`

Answer

`@DynamicPropertySource` is specifically designed to add properties with values that are not known until runtime, such as the dynamic port or URL of a service started by Testcontainers. [10, 21, 22] It must be used on a static method that accepts a `DynamicPropertyRegistry`. `@TestPropertySource` is for static properties, `@ContextConfiguration` is for customizing the context, and `@ActiveProfiles` activates profiles but doesn't set dynamic properties.

Spring Boot Practice Test

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Spring Boot Testing Spring Applications Questions and Answers