final FessMessages messages1 = new FessMessages();
        messages1.addErrorsOperationAlreadyRunning("prop", "host1");
        assertFalse(messages1.isEmpty());

        final FessMessages messages2 = new FessMessages();
        messages2.addErrorsOperationAlreadyRunning("prop", "node1@host2");
        assertFalse(messages2.isEmpty());
    }