@Test
public void testMappingInterface() throws Exception {
// prepare 2 Users in 1 UserGroup
User user1 = newInstance(UserImpl.class);
user1.setFirstName("first name 1");
user1.setLastName("last name 1");
User user2 = newInstance(UserImpl.class);
user2.setFirstName("first name 2");
user2.setLastName("last name 2");
UserGroup userGroup = newInstance(UserGroupImpl.class);
userGroup.setName("usergroup name");
userGroup.addUser(user1);
userGroup.addUser(user2);