type proxyFromEnvTest struct {
	req string // URL to fetch; blank means "http://example.com"

	env      string // HTTP_PROXY
	httpsenv string // HTTPS_PROXY
	noenv    string // NO_PROXY
	reqmeth  string // REQUEST_METHOD

	want    string
	wanterr error
}

func (t proxyFromEnvTest) String() string {
	var buf strings.Builder
	space := func() {
		if buf.Len() > 0 {
			buf.WriteByte(' ')
		}