@Test public void should_resume_headers() {

  Message message = MessageBuilder.withBody(new byte[0]).build();
  message.getMessageProperties().setHeader("b3", B3SingleFormat.writeB3SingleFormat(parent));
  Message postProcessMessage = tracingMessagePostProcessor.postProcessMessage(message);
  assertThat(spans.get(0).parentId()).isEqualTo(parent.spanIdString());
  Map<String, Object> headers = postProcessMessage.getMessageProperties().getHeaders();
  assertThat(headers.get("b3").toString()).endsWith("-" + spans.get(0).id() + "-1");
}