How I can check if I lose connection with mqtt broker?

I am trying with paho pkg to build mqtt sub client by golang,
and I have a problem with my client when the broker disconnect, I think should lost message appear, but this not happen, and if I start the broker,
mqtt sub client can't able to get message sent by mqtt pub client.

why this happens and how I can fix that?

Code

package main

import (
	"fmt"
	"os"

	mqtt "github.com/eclipse/paho.mqtt.golang"
)

var (
	broker                     = "tcp://localhost:1883"
	f      mqtt.MessageHandler = func(client mqtt.Client, msg mqtt.Message) {
		fmt.Printf("TOPIC: %s\n", msg.Topic())
		fmt.Printf("MSG: %s\n", msg.Payload())
	}
)

func main() {
	//create a ClientOptions
	opts := mqtt.NewClientOptions().AddBroker(broker)
	opts.SetClientID("group-one")
	opts.SetDefaultPublishHandler(f)

	//create and start a client using the above ClientOptions
	c := mqtt.NewClient(opts)
	if token := c.Connect(); token.Wait() && token.Error() != nil {
		panic(token.Error())
	}

	if token := c.Subscribe("test", 0, nil); token.Wait() && token.Error() != nil {
		fmt.Println(token.Error())
		os.Exit(1)
	}

	for {

	}
}

Assign a custom OnConnectionLostHandler to catch connection lost event, so you can perform additional action whenever the client loses connection. If you set the AutoReconnect option to true (which is the default behavior), the client will automatically reconnects to the broker after connection lost. Please note that after connection lost, your subscription state/info may not being saved by the broker, so you won't be able to receive any message. To deal with this issue, move topic subscription to OnConnect handler. Below is an example implementation:

package main
import (
"fmt"
"os"
"time"
mqtt "github.com/eclipse/paho.mqtt.golang"
)
func messageHandler(c mqtt.Client, msg mqtt.Message) {
fmt.Printf("TOPIC: %s\n", msg.Topic())
fmt.Printf("MSG: %s\n", msg.Payload())
}
func connLostHandler(c mqtt.Client, err error) {
fmt.Printf("Connection lost, reason: %v\n", err)
//Perform additional action...
}
func main() {
//create a ClientOptions
opts := mqtt.NewClientOptions().
AddBroker("tcp://localhost:1883").
SetClientID("group-one").
SetDefaultPublishHandler(messageHandler).
SetConnectionLostHandler(connLostHandler)
//set OnConnect handler as anonymous function
//after connected, subscribe to topic
opts.OnConnect = func(c mqtt.Client) {
fmt.Printf("Client connected, subscribing to: test/topic\n")
//Subscribe here, otherwise after connection lost, 
//you may not receive any message
if token := c.Subscribe("test/topic", 0, nil); token.Wait() && token.Error() != nil {
fmt.Println(token.Error())
os.Exit(1)
}
}
//create and start a client using the above ClientOptions
c := mqtt.NewClient(opts)
if token := c.Connect(); token.Wait() && token.Error() != nil {
panic(token.Error())
}
for {
//Lazy...
time.Sleep(500 * time.Millisecond)
}
}