@Test
  void singleInterceptor() throws Exception {
    server.enqueue(new MockResponse().setBody("foo"));

    TestInterface api =
        new TestInterfaceBuilder()
            .requestInterceptor(new ForwardedForInterceptor())
            .target("http://localhost:" + server.getPort());

    api.post();

    assertThat(server.takeRequest())
        .hasHeaders(entry("X-Forwarded-For", Collections.singletonList("origin.host.com")));
  }
The type of a parameter value may not be the desired type to encode as. Prefer the interface
type.
core/src/test/java/feign/FeignUnderAsyncTest.java