@Test
 public void testParentIdLookup() {
   String[] ids =
       PersistenceUnitDescriptorProvider.getInstance().primaryKeyFields(MappedThree.class);
   Assert.assertNotNull(ids);
   Assert.assertEquals(1, ids.length);
 }
 @Before
 public void before() throws IOException {
   PersistenceUnitDescriptorProvider.getInstance().init();
 }