Spring Boot TDD

Source: affaan-m/everything-claude-code Original files: skills/springboot-tdd/SKILL.md Curated: 2026-02-21

Workflow

1. Write tests first (they should fail)
2. Implement minimal code to pass
3. Refactor with tests green
4. Enforce coverage with JaCoCo

Unit Tests (JUnit 5 + Mockito)

@ExtendWith(MockitoExtension.class)
class MarketServiceTest {
  @Mock MarketRepository repo;
  @InjectMocks MarketService service;

  @Test
  void createsMarket() {
    CreateMarketRequest req = new CreateMarketRequest(
        "name", "desc", Instant.now(), List.of("cat"));
    when(repo.save(any())).thenAnswer(inv -> inv.getArgument(0));

    Market result = service.create(req);

    assertThat(result.name()).isEqualTo("name");
    verify(repo).save(any());
  }
}

Patterns:

• Arrange-Act-Assert
• Avoid partial mocks; prefer explicit stubbing
• Use @ParameterizedTest for variants

Web Layer (MockMvc)

@WebMvcTest(MarketController.class)
class MarketControllerTest {
  @Autowired MockMvc mockMvc;
  @MockBean MarketService marketService;

  @Test
  void returnsMarkets() throws Exception {
    when(marketService.list(any())).thenReturn(Page.empty());

    mockMvc.perform(get("/api/markets"))
        .andExpect(status().isOk())
        .andExpect(jsonPath("$.content").isArray());
  }
}

Integration Tests

@SpringBootTest
@AutoConfigureMockMvc
@ActiveProfiles("test")
class MarketIntegrationTest {
  @Autowired MockMvc mockMvc;

  @Test
  void createsMarket() throws Exception {
    mockMvc.perform(post("/api/markets")
        .contentType(MediaType.APPLICATION_JSON)
        .content("""
          {"name":"Test","description":"Desc",
           "endDate":"2030-01-01T00:00:00Z","categories":["general"]}
        """))
      .andExpect(status().isCreated());
  }
}

Persistence Tests

@DataJpaTest
@AutoConfigureTestDatabase(replace = Replace.NONE)
@Import(TestContainersConfig.class)
class MarketRepositoryTest {
  @Autowired MarketRepository repo;

  @Test
  void savesAndFinds() {
    MarketEntity entity = new MarketEntity();
    entity.setName("Test");
    repo.save(entity);

    Optional<MarketEntity> found = repo.findByName("Test");
    assertThat(found).isPresent();
  }
}

Testcontainers

• Use reusable containers for Postgres/Redis to mirror production
• Wire via @DynamicPropertySource to inject JDBC URLs into Spring context

Coverage (JaCoCo)

<plugin>
  <groupId>org.jacoco</groupId>
  <artifactId>jacoco-maven-plugin</artifactId>
  <version>0.8.14</version>
  <executions>
    <execution><goals><goal>prepare-agent</goal></goals></execution>
    <execution>
      <id>report</id><phase>verify</phase>
      <goals><goal>report</goal></goals>
    </execution>
  </executions>
</plugin>

Assertions

• Prefer AssertJ (assertThat) for readability
• JSON responses: jsonPath
• Exceptions: assertThatThrownBy(...)

Test Data Builders

class MarketBuilder {
  private String name = "Test";
  MarketBuilder withName(String n) { this.name = n; return this; }
  Market build() { return new Market(null, name, MarketStatus.ACTIVE); }
}

CI Commands

mvn -T 4 test              # Maven parallel
mvn verify                  # Full verify + report
./gradlew test jacocoTestReport  # Gradle

Best Practices

• Keep tests fast, isolated, and deterministic
• Test behavior, not implementation details
• Use Arrange-Act-Assert pattern
• Use @ParameterizedTest for variants
• Prefer Testcontainers over H2 for realistic testing
• Target 80%+ coverage, 100% on critical paths