Testcontainers in Spring Boot

Testcontainers in Spring Boot

1. Add Dependencies

In pom.xml (for Maven) or build.gradle (for Gradle), add the following:

Maven:

<dependencies>
    <!-- Spring Boot starter for JPA -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-jpa</artifactId>
    </dependency>

    <!-- PostgreSQL driver -->
    <dependency>
        <groupId>org.postgresql</groupId>
        <artifactId>postgresql</artifactId>
        <scope>runtime</scope>
    </dependency>

    <!-- Testcontainers dependencies -->
    <dependency>
        <groupId>org.testcontainers</groupId>
        <artifactId>testcontainers</artifactId>
        <scope>test</scope>
    </dependency>
    <dependency>
        <groupId>org.testcontainers</groupId>
        <artifactId>postgresql</artifactId>
        <scope>test</scope>
    </dependency>

    <!-- Spring Boot Test -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-test</artifactId>
        <scope>test</scope>
    </dependency>
</dependencies>

2. Create a Simple Entity and Repository

// User.java
package com.example.demo;

import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.GenerationType;
import jakarta.persistence.Id;

@Entity
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String name;

    // getters and setters
    public Long getId() { return id; }
    public void setId(Long id) { this.id = id; }

    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
}

// UserRepository.java
package com.example.demo;

import org.springframework.data.jpa.repository.JpaRepository;

public interface UserRepository extends JpaRepository<User, Long> {
}

3. Configure Testcontainers for Integration Test

// UserRepositoryTest.java
package com.example.demo;

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.orm.jpa.DataJpaTest;
import org.springframework.test.context.DynamicPropertyRegistry;
import org.springframework.test.context.DynamicPropertySource;
import org.testcontainers.containers.PostgreSQLContainer;
import org.testcontainers.junit.jupiter.Container;
import org.testcontainers.junit.jupiter.Testcontainers;

import static org.assertj.core.api.Assertions.assertThat;

@Testcontainers
@DataJpaTest
public class UserRepositoryTest {

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

    @Autowired
    private UserRepository userRepository;

    // Dynamically inject DB properties to Spring Boot
    @DynamicPropertySource
    static void setDatasourceProperties(DynamicPropertyRegistry registry) {
        registry.add("spring.datasource.url", postgresContainer::getJdbcUrl);
        registry.add("spring.datasource.username", postgresContainer::getUsername);
        registry.add("spring.datasource.password", postgresContainer::getPassword);
    }

    @Test
    void testSaveAndFindUser() {
        User user = new User();
        user.setName("Alice");
        userRepository.save(user);

        assertThat(userRepository.findAll()).hasSize(1);
    }
}

4. How It Works

  1. Testcontainers starts a PostgreSQL Docker container for the test.
  2. Spring Boot dynamically connects to this container using DynamicPropertySource.
  3. After the test finishes, the container is automatically stopped and removed.
  4. This ensures isolated, repeatable integration tests without needing a real database installed locally.

5. Notes

  • You need Docker installed on your machine for Testcontainers to work.
  • You can also use Testcontainers for Kafka, Redis, MySQL, MongoDB, etc.
  • Integration tests are slower than unit tests, but they provide real environment validation.

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