@Override
  public String toString() {
    return String.format("Request [%s %s: %s headers and %s]", method, url,
        headers == null ? "without" : "with " + headers,
        charset == null ? "no charset" : "charset " + charset);
  }
@Test
  void testToString() throws Exception {
    assertThat(requestKey.toString()).startsWith("Request [GET a: ");
    assertThat(requestKey.toString()).contains(" with my-header=[val] ", " UTF-16]");
  }