Spring Boot TDD Workflow

TDD guidance for Spring Boot services with 80%+ coverage (unit + integration).

When to Use

• New features or endpoints

• Bug fixes or refactors

• Adding data access logic or security rules

Workflow

• Write tests first (they should fail)

• Implement minimal code to pass

• Refactor with tests green

• Enforce coverage (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 Tests (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)

@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)

@DataJpaTest @AutoConfigureTestDatabase(replace = AutoConfigureTestDatabase.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)

Maven snippet:

<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

• For JSON responses, use jsonPath

• For exceptions: assertThatThrownBy(...)

Test Data Builders

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

CI Commands

• Maven: mvn -T 4 test or mvn verify

• Gradle: ./gradlew test jacocoTestReport

Remember: Keep tests fast, isolated, and deterministic. Test behavior, not implementation details.