How to test TCP disconnection in GO

I do have a process receiving data from second local process. I need to test if connection errors are handled well AND if it automatically reconnects and keep receiving data after a disconnection.

To do so I am trying to make it disconnect abruptly or put the TCP connection in an error state from a unit test.
As seen in this question to check if a connection is closed I am checking for data to come and test if it returns an error.
I am not sure how to:

• close the connection ungracefully
• make it be in an error state

This is the essence of my data receiver:

    import (
    	"bufio"
    	"encoding/json"
    	"fmt"
    	"io"
    	"net"
    )
    
    type Message struct {
    	ID string `json:"id"`
    }
    
    func ReceiveData(listener Listener) {
    	var tcpConn net.Conn
    	var addr string = "127.0.0.1:9999"
    	tcpConn, err := net.Dial("tcp", addr)
    	socketReader := bufio.NewReader(tcpConn)
    	decoder := json.NewDecoder(socketReader)
    
    	for {
			var msg Message
			if err := decoder.Decode(&msg); err == io.EOF {
				listener.ProcessUpdate(Message{}, fmt.Errorf("Received EOF"), nil)
				tcpConn = nil
				return
			} else if err != nil {
				listener.ProcessUpdate(Message{}, nil, fmt.Errorf("Error decoding message: %s", err.Error()))
				tcpConn = nil
				return
		}

		// process message
		_ = msg

		// Test disconnection
		// This does not disconnect:
		// tcpConn = nil
		// This does but gracefully:
		// tcpConn.Close()
	}

I am not mocking the TCP connection as I'd like to try with the real data producer. If is needed I'll look at it.

A solution is to set a deadline to the TCP connection itself:

tcpConn.SetDeadline(time.Now())

Later this will trigger a timeout error which can be caught with:

err := decoder.Decode(&msg);
if err != nil {
    if neterr, ok := err.(net.Error); ok && neterr.Timeout() {
		fmt.Errorf("TCP timeout : %s", err.Error())
	} else {
		fmt.Errorf("Received error decoding message: %s", err.Error())
	}
}