如何在 junit5 的以下代码中模拟 whenComplete 的兼容未来的异常

问：

以下是在 mqtt broker 上发布消息的代码：

           mqtt5Client.publishWith().topic(topicName)
                   .payload(messagePayLoad)
                   .qos(mqttQos)
                   .retain(isRetainedMessage)
                   .send().whenComplete((connAck, exception) -> {
               if (exception != null) {
                   log.error("Failed publishing the  event ")
               } else
                   log.info("Successfully published the  event  ")
          });