Java Testing Advanced Skill

Advanced testing techniques for comprehensive test coverage.

Overview

This skill covers advanced testing patterns including Testcontainers for integration testing, contract testing with Pact, mutation testing with PIT, and property-based testing.

When to Use This Skill

Use when you need to:

• Test with real databases (Testcontainers)
• Verify API contracts
• Find gaps with mutation testing
• Generate test cases automatically

Quick Reference

Testcontainers

@Testcontainers
@SpringBootTest
class OrderRepositoryIT {

    @Container
    static PostgreSQLContainer<?> postgres =
        new PostgreSQLContainer<>("postgres:15")
            .withDatabaseName("test")
            .withUsername("test")
            .withPassword("test");

    @Container
    static KafkaContainer kafka =
        new KafkaContainer(DockerImageName.parse("confluentinc/cp-kafka:7.4.0"));

    @DynamicPropertySource
    static void configure(DynamicPropertyRegistry registry) {
        registry.add("spring.datasource.url", postgres::getJdbcUrl);
        registry.add("spring.kafka.bootstrap-servers", kafka::getBootstrapServers);
    }

    @Test
    void shouldPersistOrder() {
        Order saved = repository.save(new Order("item", 100.0));
        assertThat(saved.getId()).isNotNull();
    }
}

Contract Testing (Pact)

@ExtendWith(PactConsumerTestExt.class)
class UserServiceContractTest {

    @Pact(consumer = "order-service", provider = "user-service")
    public RequestResponsePact createPact(PactDslWithProvider builder) {
        return builder
            .given("user exists")
            .uponReceiving("get user request")
                .path("/users/1")
                .method("GET")
            .willRespondWith()
                .status(200)
                .body(new PactDslJsonBody()
                    .integerType("id", 1)
                    .stringType("name", "John"))
            .toPact();
    }

    @Test
    @PactTestFor(pactMethod = "createPact")
    void testGetUser(MockServer mockServer) {
        User user = client.getUser(mockServer.getUrl(), 1L);
        assertThat(user.getName()).isEqualTo("John");
    }
}

Mutation Testing (PIT)

<plugin>
    <groupId>org.pitest</groupId>
    <artifactId>pitest-maven</artifactId>
    <version>1.15.0</version>
    <configuration>
        <targetClasses>
            <param>com.example.service.*</param>
        </targetClasses>
        <mutationThreshold>80</mutationThreshold>
    </configuration>
</plugin>

Property-Based Testing

@Property
void shouldReverseListTwiceReturnsOriginal(@ForAll List<Integer> list) {
    Collections.reverse(list);
    Collections.reverse(list);
    // Original order restored
}

Testing Pyramid

     /\        E2E Tests (few)
    /  \       Contract Tests
   /----\      Integration Tests
  /------\     Unit Tests (many)

Troubleshooting

Problem	Solution
Container slow	Reuse containers
Port conflicts	Random ports
Flaky tests	Wait strategies

Usage

Skill("java-testing-advanced")