}

func TestHeadersAlreadyWritten(t *testing.T) {
	rw := httptest.NewRecorder()
	trw := &trackingResponseWriter{ResponseWriter: rw}

	if headersAlreadyWritten(trw) {
		t.Fatal("headers have not been written yet")
	}

	trw.WriteHeader(123)
	if !headersAlreadyWritten(trw) {
		t.Fatal("headers were written")
	}
}

func TestHeadersAlreadyWrittenWrapped(t *testing.T) {
	rw := httptest.NewRecorder()

}

type unwrapper interface {
	Unwrap() http.ResponseWriter
}

// headersAlreadyWritten returns true if the headers have already been written
// to this response writer. It will unwrap the ResponseWriter if possible to try
// and find a trackingResponseWriter.
func headersAlreadyWritten(w http.ResponseWriter) bool {
	for {
		if trw, ok := w.(*trackingResponseWriter); ok {