Unravel › Java concepts › Testing

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At a glance

1. 1Declare a container as a static field: @Container static PostgreSQLContainer<?> db = new PostgreSQLContainer<>("postgres:16")With @Testcontainers it starts before tests and stops after.
2. 2Wire the dynamic port into the application: @ServiceConnection (Spring Boot 3.1+) does it automatically; otherwise @DynamicPropertySource sets spring.datasource.url to db.getJdbcUrl()
3. 3Share one container across the whole test class or suite (a singleton container or static field) because start-up costs seconds
4. 4Modules exist for most infrastructure (Kafka, MongoDB, LocalStack for AWS, Elasticsearch, RabbitMQ), and GenericContainer runs any image with a wait strategy

• H2 or other embedded replacements hide real differences (SQL dialect, locking, JSON types, collations)
• Make the image tag explicit and equal to production (postgres:16.2), never latest
• Testcontainers talks to the Docker daemon through its API, creates the container with a random mapped host port, and waits using a strategy (log message, port, HTTP health) until the service is ready

@Testcontainers@SpringBootTestclass OrderRepositoryIT {    @Container    @ServiceConnection    static PostgreSQLContainer<?> db = new PostgreSQLContainer<>("postgres:16");    @Autowired    OrderRepository orders;    @Test    void savesAndFindsByStatus() {        orders.save(new Order("NEW"));        assertEquals(1, orders.findByStatus("NEW").size());    }}

1. line 1 uses Testcontainers, the core of Testcontainers (real databases and brokers in tests)
2. line 4 uses Container, the core of Testcontainers (real databases and brokers in tests)
3. line 5 uses ServiceConnection, the core of Testcontainers (real databases and brokers in tests)
4. line 6 uses PostgreSQLContainer, the core of Testcontainers (real databases and brokers in tests)

How Unravel recognises it

When you paste code, Unravel looks for these signs of testcontainers (real databases and brokers in tests). Spotting them yourself is a good habit when you read unfamiliar code:

• Annotations: @Testcontainers @Container @ServiceConnection
• Types: PostgreSQLContainer MySQLContainer MariaDBContainer GenericContainer MongoDBContainer RedisContainer LocalStackContainer DockerImageName ElasticsearchContainer RabbitMQContainer OracleContainer MSSQLServerContainer CassandraContainer GenericContainer and 7 more
• Configuration keys: jdbc:tc:

Part of a learning path

• Testing enterprise code · previous: Testing HTTP endpoints (MockMvc, WebTestClient, REST Assured) · next: Faking remote services (WireMock, MockWebServer, Pact)

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