state.add(ref);
state.addReference(ref);
   public void testRecoverableState_remove_7() throws Throwable   {      if (!state.isRecoverable())      {         // only recoverable state is tested now         return;      }      MessageReference ref = ms.reference(MessageFactory.createMessage("message0", false, "payload0"));      state.add(ref);      MessageReference rref = state.removeFirst();      assertEquals("message0", rref.getMessageID());      assertNull(state.removeFirst());      log.info("ok");   }