package main

import (
	"crypto/x509"
	"errors"
	"fmt"
	"net/http"
	"net/http/httptest"
)

func main() {
	// new test server
	s := httptest.NewTLSServer(nil)
	defer s.Close()

	// request with system roots
	req, _ := http.NewRequest("GET", s.URL, nil)

	// handle errors
	_, err := http.DefaultClient.Do(req)
	switch {
	case errors.As(err, &x509.UnknownAuthorityError{}):
		// ... log or fallback to alternate code path
		fmt.Println("UnknownAuthorityError", err)
	default:
		fmt.Println("unexpected error type", err)
	}
}