You can test your JPA code by setting aside another folder structure, test/ for example, with a META-INF/ directory with a new persistence.xml file there pointing to a different database.

Here’s new new persistence.xml:

 <?xml version="1.0" encoding="UTF-8" ?>
 <persistence xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"
     version="2.0"
     xmlns="http://java.sun.com/xml/ns/persistence">
   <persistence-unit name="example" transaction-type="RESOURCE_LOCAL">
     <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
     <class>org.denevell.tomcat.entities.write.AnotherThing</class>
     <properties>
       <property name="javax.persistence.jdbc.driver" value="org.sqlite.JDBC" />
       <property name="javax.persistence.jdbc.url" value="jdbc:sqlite:/home/YOURUSERNAME/test.db" />
       <property name="eclipselink.logging.level" value="ALL" />
       <property name="eclipselink.ddl-generation" value="drop-and-create-tables" />
     </properties>
   </persistence-unit>
</persistence>

The only different to the previous ones is that we’re putting our database in a new location - one where the runner of the junit test has write access. And we’re doing drop-and-create-tables in the table creation.

The next thing you need is the junit4 file that calls the persistence provider to test adding of the entity:

public class JPAStarterTest {
  @Test
  public void addAnotherThing() {
    // Arrange
    AnotherThing at = new AnotherThing();
    at.setText("hii");          
    // Act
    tx.begin();
    em.persist(at);
    tx.commit();            
    // Assert
    assertNotNull("Id should not be null", at.getId());
    List<AnotherThing> list = em.createNamedQuery("listAll", AnotherThing.class).getResultList();
    assertEquals("Table has one entity", 1, list.size()); 
    assertEquals("Table has correcttext", "hii", list.get(0).getText());
  }

  @BeforeClass
  public static void beforeClass() {
    emf = Persistence.createEntityManagerFactory("exampletest");
    em = emf.createEntityManager();
  }

  @AfterClass
  public static void afterClass() {
    em.close();
    emf.close();
  }

  @Before
  public void before() {
    tx = em.getTransaction();
  }
  private static EntityManagerFactory emf;
  private static EntityManager em;
  private EntityTransaction tx; 
}

Now when you run this, ensure your new persistence.xml is in the META-INF/ directory of the classes.