code: @Test public void get() throws Exception {
    server.enqueue(new MockResponse().setBody("abc").addHeader("Content-Type: text/plain"));
    server.play();
    Request request=new Request.Builder().url(server.getUrl("/")).header("User-Agent","AsyncApiTest").build();
    client.enqueue(request,receiver);
    receiver.await(request.url()).assertCode(200).assertContainsHeaders("Content-Type: text/plain").assertBody("abc");
    assertTrue(server.takeRequest().getHeaders().contains("User-Agent: AsyncApiTest"));
  }
  