Yaya kake gwada aikace-aikacen Spring Boot: @SpringBootTest, MockMvc, slices?

Question

IT Interview Practice · Accepted Answer

Spring Boot yana ba ka **dala na gwaji (testing pyramid)**: unit tests masu sauri ba tare da Spring ba, *slice* tests masu mai da hankali da ke lodin ɓangare na context, da ƴan integration tests na cikakken context. Zaɓar matakin da ya dace kowane test shi ne fasahar senior anan.

## Unit test — babu Spring ko kaɗan

Constructor injection yana nufin yawancin dabarar service ba ta buƙatar Spring ko kaɗan; kawai mock abokan aiki:

```java
@Test
void appliesDiscount() {
    var repo = mock(PriceRepository.class);
    when(repo.base("A")).thenReturn(BigDecimal.TEN);
    var svc = new PricingService(repo);          // plain constructor, no context
    assertThat(svc.priceOf("A")).isEqualByComparingTo("9.00");
}
```

## Slice test — @WebMvcTest + MockMvc

Yana lodin web layer kawai (controllers, JSON, validation) — babu database, babu services fiye da mocks. Mai sauri:

```java
@WebMvcTest(UserController.class)
class UserControllerTest {
    @Autowired MockMvc mvc;
    @MockBean UserService service; // service is mocked, not real

@Test
    void returns404WhenMissing() throws Exception {
        when(service.findById(9L)).thenThrow(new EntityNotFoundException());
        mvc.perform(get("/api/users/9"))
           .andExpect(status().isNotFound()); // verifies controller + advice wiring
    }
}
```

## @DataJpaTest — slice na persistence

Yana lodin JPA/repositories a kan DB na cikin-ƙwaƙwalwa (ko Testcontainers) kuma yana rollback bayan kowane test:

```java
@DataJpaTest
class UserRepositoryTest {
    @Autowired UserRepository repo;
    @Test void findsByEmail() {
        repo.save(new User("a@x.com"));
        assertThat(repo.findByEmail("a@x.com")).isPresent();
    }
}
```

Yi amfani da `@SpringBootTest` (cikakken context, `webEnvironment = RANDOM_PORT`) da ƙyar don ainihin dubawa na end-to-end — shi ne mafi sannu.

## Me ya sa yake da muhimmanci

Masu tambayoyin hira suna son ganin cewa ka guji anti-pattern na `@SpringBootTest` don *komai*, wanda ke sanya suites sannu da masu rauni. Ambaton slice da ya dace kowace damuwa, mocking da `@MockBean`, da amfani da **Testcontainers** don ainihin database maimakon H2 yana nuna wanda ke ajiye babbar test suite mai sauri kuma abin dogaro.

Unit test — babu Spring ko kaɗan

Slice test — @WebMvcTest + MockMvc

@DataJpaTest — slice na persistence

Me ya sa yake da muhimmanci

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