Verify saving and retrieving an entity using @DataJpaTest

Preconditions (3)

Step 1: Create a new User object with name 'Alice'

Step 2: Save the User object using UserRepository

Step 3: Retrieve the User by its id using UserRepository

Step 4: Verify the retrieved User is not null

Step 5: Verify the retrieved User's name is 'Alice'

✅ Expected Result: The User entity is saved and retrieved correctly with the name 'Alice'

Automation Requirements - JUnit 5 with Spring Boot Test

Assertions Needed:

Assert that the retrieved User is not null

Assert that the retrieved User's name equals 'Alice'

Best Practices:

Use @DataJpaTest annotation for repository testing

Use @Autowired to inject the repository

Use @Test annotation for test methods

Use assertThat from AssertJ for readable assertions

Use @Transactional rollback behavior provided by @DataJpaTest

Automated Solution

JUnit

package com.example.demo;

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

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

import java.util.Optional;

@DataJpaTest
class UserRepositoryTest {

    @Autowired
    private UserRepository userRepository;

    @Test
    void testSaveAndFindUser() {
        // Create a new User
        User user = new User();
        user.setName("Alice");

        // Save the User
        User savedUser = userRepository.save(user);

        // Retrieve the User by id
        Optional<User> retrievedUserOpt = userRepository.findById(savedUser.getId());

        // Verify the User is present
        assertThat(retrievedUserOpt).isPresent();

        User retrievedUser = retrievedUserOpt.get();

        // Verify the name is 'Alice'
        assertThat(retrievedUser.getName()).isEqualTo("Alice");
    }
}

// Entity class
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;

    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;
    }
}

// Repository interface
package com.example.demo;

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

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

This test class uses @DataJpaTest to load only the JPA components and an in-memory database for fast testing.

The UserRepository is injected with @Autowired. The test method testSaveAndFindUser creates a new User entity, saves it, and then retrieves it by its generated ID.

Assertions check that the retrieved user exists and that its name matches the expected value 'Alice'.

The entity class User uses JPA annotations for ID generation and mapping.

This setup ensures the repository works correctly with the database layer without loading the full application context.

Common Mistakes - 4 Pitfalls

Not using @DataJpaTest and loading the full Spring context

Not checking if Optional is present before accessing the entity

{'mistake': "Hardcoding IDs instead of using the saved entity's generated ID", 'why_bad': 'IDs are generated by the database and may not be predictable.', 'correct_approach': 'Use the ID returned from the save() method to retrieve the entity.'}

Not using assertions from AssertJ or JUnit and relying on print statements

Bonus Challenge

Now add data-driven testing with 3 different User names to verify saving and retrieving works for each.

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