Kepiye carane nguji aplikasi Spring Boot: @SpringBootTest, MockMvc, slice?

Question

IT Interview Practice · Accepted Answer

Spring Boot menehi kowe **piramida testing**: unit test cepet tanpa Spring, *slice* test sing fokus sing ngemot bagean saka konteks, lan sethithik integration test konteks penuh. Milih tingkat sing pas per test iku katrampilan senior ing kene.

## Unit test — babar pisan tanpa Spring

Constructor injection tegese umume logika service ora mbutuhake Spring; mung mock kolaboratore:

```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

Ngemot mung lapisan web (controller, JSON, validasi) — ora ana database, ora ana service kajaba mock. Cepet:

```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 persistensi

Ngemot JPA/repository marang DB in-memory (utawa Testcontainers) lan rollback sawise saben 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();
    }
}
```

Gunakake `@SpringBootTest` (konteks penuh, `webEnvironment = RANDOM_PORT`) kanthi ngirit-ngirit kanggo pemeriksaan end-to-end sejati — iku paling alon.

## Kenapa iki penting

Pewawancara pengin ndeleng yen kowe ngindhari anti-pola nganggo `@SpringBootTest` kanggo *kabeh*, sing gawe suite alon lan rapuh. Nyebut slice sing bener per prakawis, mock nganggo `@MockBean`, lan nganggo **Testcontainers** kanggo database nyata tinimbang H2 nuduhake wong sing njaga suite test gedhe tetep cepet lan bisa dipercaya.

Unit test — babar pisan tanpa Spring

Slice test — @WebMvcTest + MockMvc

@DataJpaTest — slice persistensi

Kenapa iki penting

Pitakon sing gegandhengan