在golang中使用标题时，会打印两个结果

This is the code I'm working with:

package main

import (
    "fmt"
    "net/http"
)

func main() {
    http.HandleFunc("/", TestFunc)
    http.ListenAndServe(":8080", nil)
}

func TestFunc(w http.ResponseWriter, r *http.Request) {
    fmt.Println("test")

    // --------------------- headers ------------------------
    w.Header().Set("Accept-Charset", "utf-8")
    w.Header().Set("Accept-Encoding", "gzip")
    w.Header().Set("Content-Type", "text/html; charset=utf-8")
    w.WriteHeader(http.StatusOK)
}

The code above works and prints two result (test test) every time.

When I remove the headers, code works fine and returns only "test".

What is the issue in this code?

Your browser is likely requesting /favicon.ico. Printing out the value of r.URL in the request handler will confirm this.