Spring Boot Testing

Question Variations

"When should you use `@WebMvcTest`?"
"What does `@SpringBootTest` load?"
"Why avoid full-context tests for every class?"

Why This Is Asked

Testing annotations assess whether candidates choose the smallest realistic Spring context for the behavior under test.

Key Concepts

Unit tests should not start Spring unnecessarily.
Slice tests target a layer such as MVC or JPA.
@SpringBootTest loads the full application context when integration is needed.
Tests need isolated deterministic dependencies and configuration.

Question Variations

“When should you use @WebMvcTest?”
“What does @SpringBootTest load?”
“Why avoid full-context tests for every class?”

Answers by Technology

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Expected Answer (Spring Boot 4.1.0 / Java 17+)

Choose the smallest test scope that provides confidence. Plain unit tests are fastest for domain logic. Use @WebMvcTest for controller and MVC behavior with mocked collaborators, @DataJpaTest for persistence behavior, and @SpringBootTest only when the full application context or cross-layer integration is needed. Keep external services isolated and test error, authorization, and validation paths as well as success cases.

Why It Matters

Focused tests give fast feedback, while a smaller number of full-context tests catches real wiring defects without making the suite slow and brittle.

Code Example

@WebMvcTest(UserController.class)
class UserControllerTest {
  @Autowired MockMvc mvc;
  @Test void rejectsInvalidBody() throws Exception {
    mvc.perform(post("/users").contentType(APPLICATION_JSON).content("{}"))
      .andExpect(status().isBadRequest());
  }
}

Common Mistakes

Using @SpringBootTest for every test: The suite is slow and configuration-heavy.
Testing only controllers without response assertions: HTTP status and validation contracts regress unnoticed.

Follow-up Questions

What does @WebMvcTest target? (Answer: The MVC slice around selected controllers.)
When use a full context? (Answer: When integration wiring itself is under test.)