@Test
  void consumesMultipleWithContentTypeHeaderAndBody() throws Exception {
    server.enqueue(new MockResponse().setBody("AAAAAAAA"));
    final JaxRSClientTestInterfaceWithJaxRsContract api =
        newBuilder()
            .contract(new JAXRSContract()) // use JAXRSContract
            .target(
                JaxRSClientTestInterfaceWithJaxRsContract.class,
                "http://localhost:" + server.getPort());

    final Response response =
        api.consumesMultipleWithContentTypeHeaderAndBody("application/json;charset=utf-8", "body");
    assertThat(Util.toString(response.body().asReader(UTF_8))).isEqualTo("AAAAAAAA");

    MockWebServerAssertions.assertThat(server.takeRequest())
        .hasHeaders(
            MapEntry.entry(
                "Content-Type", Collections.singletonList("application/json;charset=utf-8")))
        .hasMethod("POST");
  }
Tests client-specific behavior, such as ensuring Content-Length is sent when specified.
jaxrs2/src/test/java/feign/jaxrs2/JAXRSClientTest.java