tx.lock(obj_2, Transaction.WRITE);
references = obj_2.getAllReferences();
CollectionReference ref = (CollectionReference) references.get(0);
tx.lock(ref, Transaction.WRITE);
ref.setRefName(nameRef+"_update");
tx.commit();
broker = PersistenceBrokerFactory.defaultPersistenceBroker();
obj_2 = (MainObject) broker.getObjectByIdentity(oid_2);
assertNotNull(obj_2);
references = obj_2.getAllReferences();