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

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

Unit Tests (JUnit 5 + Mockito)

java
1@ExtendWith(MockitoExtension.class)
2class MarketServiceTest {
3  @Mock MarketRepository repo;
4  @InjectMocks MarketService service;
5
6  @Test
7  void createsMarket() {
8    CreateMarketRequest req = new CreateMarketRequest("name", "desc", Instant.now(), List.of("cat"));
9    when(repo.save(any())).thenAnswer(inv -> inv.getArgument(0));
10
11    Market result = service.create(req);
12
13    assertThat(result.name()).isEqualTo("name");
14    verify(repo).save(any());
15  }
16}

Patterns:

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

Web Layer Tests (MockMvc)

java
1@WebMvcTest(MarketController.class)
2class MarketControllerTest {
3  @Autowired MockMvc mockMvc;
4  @MockBean MarketService marketService;
5
6  @Test
7  void returnsMarkets() throws Exception {
8    when(marketService.list(any())).thenReturn(Page.empty());
9
10    mockMvc.perform(get("/api/markets"))
11        .andExpect(status().isOk())
12        .andExpect(jsonPath("$.content").isArray());
13  }
14}

Integration Tests (SpringBootTest)

java
1@SpringBootTest
2@AutoConfigureMockMvc
3@ActiveProfiles("test")
4class MarketIntegrationTest {
5  @Autowired MockMvc mockMvc;
6
7  @Test
8  void createsMarket() throws Exception {
9    mockMvc.perform(post("/api/markets")
10        .contentType(MediaType.APPLICATION_JSON)
11        .content("""
12          {"name":"Test","description":"Desc","endDate":"2030-01-01T00:00:00Z","categories":["general"]}
13        """))
14      .andExpect(status().isCreated());
15  }
16}

Persistence Tests (DataJpaTest)

java
1@DataJpaTest
2@AutoConfigureTestDatabase(replace = AutoConfigureTestDatabase.Replace.NONE)
3@Import(TestContainersConfig.class)
4class MarketRepositoryTest {
5  @Autowired MarketRepository repo;
6
7  @Test
8  void savesAndFinds() {
9    MarketEntity entity = new MarketEntity();
10    entity.setName("Test");
11    repo.save(entity);
12
13    Optional<MarketEntity> found = repo.findByName("Test");
14    assertThat(found).isPresent();
15  }
16}

Testcontainers

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

Coverage (JaCoCo)

Maven snippet:

xml
1<plugin>
2  <groupId>org.jacoco</groupId>
3  <artifactId>jacoco-maven-plugin</artifactId>
4  <version>0.8.14</version>
5  <executions>
6    <execution>
7      <goals><goal>prepare-agent</goal></goals>
8    </execution>
9    <execution>
10      <id>report</id>
11      <phase>verify</phase>
12      <goals><goal>report</goal></goals>
13    </execution>
14  </executions>
15</plugin>

Assertions

• Prefer AssertJ (assertThat) for readability
• For JSON responses, use jsonPath
• For exceptions: assertThatThrownBy(...)

Test Data Builders

java
1class MarketBuilder {
2  private String name = "Test";
3  MarketBuilder withName(String name) { this.name = name; return this; }
4  Market build() { return new Market(null, name, MarketStatus.ACTIVE); }
5}

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.