public static <C> AsyncBuilder<C> builder() {
    return new AsyncBuilder<>();
  }
@SuppressWarnings("deprecation")
  @Test
  void whenReturnTypeIsResponseNoErrorHandling() throws Throwable {
    Map<String, Collection<String>> headers = new LinkedHashMap<>();
    headers.put("Location", Arrays.asList("http://bar.com"));
    final Response response = Response.builder().status(302).reason("Found").headers(headers)
        .request(Request.create(HttpMethod.GET, "/", Collections.emptyMap(), null, Util.UTF_8))
        .body(new byte[0]).build();

    ExecutorService execs = Executors.newSingleThreadExecutor();

    // fake client as Client.Default follows redirects.
    TestInterfaceAsync api = AsyncFeign.<Void>builder()
        .client(new AsyncClient.Default<>((request, options) -> response, execs))
        .target(TestInterfaceAsync.class, "http://localhost:" + server.getPort());

    assertThat(unwrap(api.response()).headers()).hasEntrySatisfying("Location", value -> {
      assertThat(value).contains("http://bar.com");
    });

    execs.shutdown();
  }