@Override
    public void destroy() {
        if (this.mqttClient != null) {
            this.mqttClient.disconnect();
        }
    }
@Test
    public void givenMqttClientIsNotNull_whenDestroy_thenDisconnect() {
        ReflectionTestUtils.setField(mqttNode, "mqttClient", mqttClientMock);
        mqttNode.destroy();
        then(mqttClientMock).should().disconnect();
    }