You can test your configuration by connecting HiveMQ's MQTT over Websocket client like in figure below.
Follow up steps 1 to 4 to connect, subscribe, publish and receive the messages via maqiatto.com.
You can use your Mosquitto MQTT client's console tools called mosquitto_pub/sub.
USe command line tool like denoted below with given parameters.
Linux based (for raspberry, beaglebone, ubuntu based etc.) client codes will be in here soon.
Also ESP8266 and Arduino clients will be here.