Unit testing with JUnit for Hibernate using HSQLDB (In-Memory)

Performing JUnit/unit test on hibernate code base can be accomplished using HSQLDB database. HSQLDB provides two ways of implementing this.

Using file system as database
• Using HSQLDB in-memory database.

Using in-memory database needs no change to your code other than changes in the hibernate.cfg.xml ( hibernate configuration file). The configuration below uses the hsqldb in-memory database to test an Employee entity.

hibernate.cfg.xml –

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
                                         "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
 <session-factory name="">
  <property name="hibernate.connection.driver_class">org.hsqldb.jdbcDriver</property>
  <property name="hibernate.connection.url">jdbc:hsqldb:mem:testdb;shutdown=false</property>
  <property name="hibernate.connection.username">sa</property><!-- default username -->
  <property name="hibernate.connection.password"/><!-- default password -->
  <property name="hibernate.connection.pool_size">10</property>
  <property name="hibernate.connection.autocommit">true</property>
  <property name="hibernate.cache.provider_class">org.hibernate.cache.HashtableCacheProvider</property>
  <property name="hibernate.hbm2ddl.auto">create-drop</property><!-- creates the tables from the entites automatically -->
  <property name="show_sql">true</property>
  <property name="dialect">org.hibernate.dialect.HSQLDialect</property>
  <mapping class="blog.hibernate.employee.Employee"/>
 </session-factory>
</hibernate-configuration>

package blog.hibernate.employeeTest;


import static org.junit.Assert.*;

import java.io.File;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.AnnotationConfiguration;
import org.hibernate.cfg.Configuration;
import org.junit.BeforeClass;
import org.junit.Test;

import blog.hibernate.employee.Employee;
import blog.hibernate.employee.EmployeeManager;

public class EmployeeTest {
	
	private static Configuration config;
    	private static SessionFactory factory;
	private static Session hibernateSession;
	
	
	@BeforeClass
	public void init() {
		config = new AnnotationConfiguration();
		config.configure(new File("hibernate.cfg.xml"));
        	factory = config.buildSessionFactory();
        	hibernateSession = factory.openSession();
    	}
	
	@Test
	public void insertEmployee(){
		String empName = "Employee1";
		String empLocation = "India";
		//Add new employee using the session created by HSQLDB configuration
		EmployeeManager.addEmployee(new Employee(empName,empLocation),hibernateSession);
		Employee emp = EmployeeManager.getEmployeeByName(empName,hibernateSession);
		assertEquals("India", emp.getLocation());
	}
}

The hibernate.hbm2ddl.auto option makes sure that there is no need to explicitly create the schema for the entities, but is not true in case of any depending tables that are not a part of the hibernate entities. In such a case, the schema needs to be created explicitly.

It is important to note that the in-memory schema is persisted only for that particular session. Once the session is closed, the schema is lost. If there is a need for persistence across tests ( for different sessions), then the file system DB can be used as an option.