Spring Boot Unit Testing with H2 as Mock Database

October 16, 2025

#1

This guide shows how to use H2 as a mock database for unit testing in Spring Boot projects with JUnit and Spring Data JPA.

1. Add Dependencies

In pom.xml:

<dependency>
  <groupId>com.h2database</groupId>
  <artifactId>h2</artifactId>
  <scope>test</scope>
</dependency>
<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-test</artifactId>
  <scope>test</scope>
</dependency>

2. Configure H2 for Tests

In application-test.properties:

spring.datasource.url=jdbc:h2:mem:mockdb;DB_CLOSE_DELAY=-1
spring.datasource.driver-class-name=org.h2.Driver
spring.datasource.username=sa
spring.datasource.password=
spring.jpa.hibernate.ddl-auto=create-drop

This makes H2 act as a mock DB that resets after each test run.

3. Create Entity

import jakarta.persistence.*;

@Entity
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private String email;
}

4. Repository

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

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

5. Unit Test with H2

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.orm.jpa.DataJpaTest;

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

@DataJpaTest
class UserRepositoryTest {

    @Autowired
    private UserRepository repo;

    @Test
    void testInsertAndFind() {
        User user = new User();
        user.setName("Alice");
        user.setEmail("alice@mail.com");
        repo.save(user);

        User found = repo.findById(user.getId()).orElse(null);
        assertThat(found).isNotNull();
        assertThat(found.getEmail()).isEqualTo("alice@mail.com");
    }
}

6. Run Tests

Execute:

mvn test

H2 will serve as a temporary mock database, ensuring isolated unit tests.