Hibernate DAO Unit Testing Simple Fetch

Question

I am very new to API development in Java and would like to create a proper unit test for my DAO Java class. The project uses Hibernate and the class fetches data from a MySQL database, returns it in a JSON format for a GET request.

I'm not sure how to write the unit test, if anyone could help I'd appreciate it.

public class LabelDAO extends AbstractDAO<LabelEntity> {

    public LabelEntity findLabelByLabelId(final String labelId) {
        final String query = "SELECT l FROM LabelEntity l WHERE l.labelId = :labelId";
        return getEntityManager().createQuery(query, LabelEntity.class).setParameter("labelId", labelId).getSingleResult();
    }
}

Answer 1

1. First add junit library and hamcrest

   <dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>4.13.2</version>
    <scope>test</scope>
   </dependency>
   
   <dependency>
    <groupId>org.hamcrest</groupId>
    <artifactId>hamcrest-all</artifactId>
    <version>1.3</version>
    <scope>test</scope>
   </dependency>
   

2. For test sql query I use memory database H2 Add H2 JDBC Driver from Maven dependency:

   <dependency>
    <groupId>com.h2database</groupId>
    <artifactId>h2</artifactId>
    <version>2.1.214</version>
    <scope>test</scope>
   </dependency>
   

3. Use database migrations library for create mock data. I advise you use database migration library for project. For example flyway or liquibase. I selected flyway for sample. Add from Maven dependency:

   <dependency>
    <groupId>org.flywaydb</groupId>
    <artifactId>flyway-core</artifactId>
    <version>8.5.13</version>
   </dependency>
   

3.1 Create migration directory src/main/resources/db/migration/test. 3.2 Create sql script file. V1__Create_label_table.sql and set sql commands:

CREATE TABLE label (
   id bigint not null,
   name varchar(100) not null
);

INSERT INTO label (id, name) values (1, 'My label');

And need separately setting your entity manager for test...

Sample test:

@Test
public void test() {

    Flyway flyway = Flyway.configure()
            .locations("classpath:/db/migration/test")
            .baselineOnMigrate(true)
            .dataSource("jdbc:h2:~/mem", "test", null)
            .load();

    flyway.clean();
    flyway.migrate();


    LabelDao labelDao = new LabelDao();
    labelDao.findLabelByLabelId("1");
    assertThat(labelDao.findLabelByLabelId("1").getName(), equalTo("My label"));

}

If you use spring you can use JpaRepository.

For example:

public interface LabelRepository extends JpaRepository<LabelEntity, Long> {
}

And replace code:

@Service
public class LabelDao {

    @Autowired
    private LabelRepository labelRepository;

    public Optional<LabelEntity> findLabelByLabelId(final Long labelId) {
        return labelRepository.findById(labelId);
    }
}

Sample test:

@SpringBootTest
class DemoApplicationTests {

    @Autowired
    private LabelDao labelDao;

    @Test
    public void test()  {
        labelDao.findLabelByLabelId(1L);
        assertThat(Objects.requireNonNull(labelDao.findLabelByLabelId(1L).orElse(null)).getName(), equalTo("My label"));
    }
}