public static Builder builder(HttpMethod method, String url) {
    return new Builder(method, url);
  }
@Test
  void builder() throws Exception {
    assertThat(requestKey.getMethod()).isEqualTo(HttpMethod.GET);
    assertThat(requestKey.getUrl()).isEqualTo("a");
    assertThat(requestKey.getHeaders().size()).isEqualTo(1);
    assertThat(requestKey.getHeaders().fetch("my-header"))
        .isEqualTo(Arrays.asList("val"));
    assertThat(requestKey.getCharset()).isEqualTo(StandardCharsets.UTF_16);
  }