private JaxRsTestInterface buildTestInterface() {
    return Feign.builder()
        .contract(new JAXRSContract())
        .client(new ApacheHttp5Client(HttpClientBuilder.create().build()))
        .target(JaxRsTestInterface.class, "http://localhost:" + server.getPort());
  }
Tests client-specific behavior, such as ensuring Content-Length is sent when specified.
hc5/src/test/java/feign/hc5/ApacheHttp5ClientTest.java