Realistic Integration Testing with Dockerized Databases

Unit tests are great for checking isolated business logic. But when your application talks to a database, a message broker, or another external service, unit tests alone won’t cut it.

That’s where integration testing comes in.

In this guide, you’ll learn how to use JUnit 5 and Testcontainers to write realistic integration tests—spinning up Docker containers directly from your test code.

Why Use Testcontainers?

Traditional integration testing often requires:

• Pre-installed databases on developer machines
• Complex test environment configurations
• Manual cleanup after tests

Testcontainers solves this by:

• Running services like PostgreSQL, MySQL, Kafka, Redis, etc. in Docker containers, automatically
• Creating isolated, disposable environments for every test run
• Simplifying setup with Java-friendly APIs

🔗 Testcontainers Official Site: https://www.testcontainers.org/

Benefits of JUnit 5 + Testcontainers

Example: Testing with PostgreSQL

Let’s look at how to set up a PostgreSQL integration test with JUnit 5 and Testcontainers.

1️⃣ Add Dependencies

In your pom.xml (Maven):

<dependency>
 <groupId>org.testcontainers</groupId>
 <artifactId>postgresql</artifactId>
 <version>1.19.1</version>
 <scope>test</scope>
</dependency>

<dependency>
 <groupId>org.junit.jupiter</groupId>
 <artifactId>junit-jupiter</artifactId>
 <version>5.10.1</version>
 <scope>test</scope>
</dependency>

2️⃣ Write the Test

import org.junit.jupiter.api.Test;
import org.testcontainers.containers.PostgreSQLContainer;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;

import static org.junit.jupiter.api.Assertions.assertEquals;

public class PostgresIntegrationTest {

 @Test
 void testPostgresWithContainer() throws Exception {
 try (PostgreSQLContainer postgres = new PostgreSQLContainer("postgres:16-alpine")) {
 postgres.start();

 String jdbcUrl = postgres.getJdbcUrl();
 String username = postgres.getUsername();
 String password = postgres.getPassword();

 try (Connection conn = DriverManager.getConnection(jdbcUrl, username, password)) {
 Statement stmt = conn.createStatement();
 stmt.execute("CREATE TABLE demo(id SERIAL PRIMARY KEY, name VARCHAR(255))");
 stmt.execute("INSERT INTO demo(name) VALUES ('Testcontainers')");

 ResultSet rs = stmt.executeQuery("SELECT name FROM demo WHERE id=1");
 rs.next();
 String result = rs.getString("name");

 assertEquals("Testcontainers", result);
 }

 postgres.stop();
 }
 }
}

3️⃣ How It Works

• PostgreSQLContainer spins up a lightweight Docker container
• Test uses the real database, not mocks
• Container is started and stopped automatically
• Your test remains self-contained and repeatable

Use Testcontainers for Other Services

Testcontainers supports more than just databases:

🔗 Full Module List:

4️⃣ Integrating with Spring Boot

If you’re using Spring Boot, Testcontainers integrates easily with @DynamicPropertySource:

@Container
static PostgreSQLContainer postgres = new PostgreSQLContainer("postgres:16-alpine");

@DynamicPropertySource
static void registerProperties(DynamicPropertyRegistry registry) {
 registry.add("spring.datasource.url", postgres::getJdbcUrl);
 registry.add("spring.datasource.username", postgres::getUsername);
 registry.add("spring.datasource.password", postgres::getPassword);
}

🔗 Spring Boot & Testcontainers Docs:

5️⃣ Running in CI/CD

Testcontainers can run in GitHub Actions, GitLab CI, Jenkins, or any CI pipeline that supports Docker.

For faster builds, use Ryuk and Docker-in-Docker (DinD) configurations.
🔗 CI Setup Guide:

6️⃣ Summary: Why Use Testcontainers?

Useful Resources

• 🔗 Testcontainers Official Docs
• 🔗
• 🔗
• 🔗 Testcontainers GitHub Repository
• 🔗

Conclusion

With JUnit 5 and Testcontainers, you can write robust, realistic integration tests without the headaches of managing local services. You’ll gain:

• More confidence in your tests
• Less environment setup
• Better CI/CD pipelines

It’s time to stop mocking your databases and start testing like it’s production.