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.