public HttpRequest inject(HttpRequest request) {
    Map<String, List<String>> map = new HashMap<>();
    if (manager.activeSpan() == null) {
      return request;
    }
    map.put(ApolloAuditConstants.TRACE_ID,
        Collections.singletonList(manager.activeSpan().traceId()));
    map.put(ApolloAuditConstants.SPAN_ID,
        Collections.singletonList(manager.activeSpan().spanId()));
    map.put(ApolloAuditConstants.OPERATOR,
        Collections.singletonList(manager.activeSpan().operator()));
    map.put(ApolloAuditConstants.PARENT_ID,
        Collections.singletonList(manager.activeSpan().parentId()));
    map.put(ApolloAuditConstants.FOLLOWS_FROM_ID,
        Collections.singletonList(manager.activeSpan().followsFromId()));

    HttpHeaders headers = request.getHeaders();
    headers.putAll(map);

    return request;
  }
@Test
  public void testInject() {

    HttpRequest mockRequest = Mockito.mock(HttpRequest.class);
    {
      ApolloAuditSpan activeSpan = Mockito.mock(ApolloAuditSpan.class);
      Mockito.when(manager.activeSpan()).thenReturn(activeSpan);
      Mockito.when(mockRequest.getHeaders()).thenReturn(new HttpHeaders());
    }
    HttpRequest injected = tracer.inject(mockRequest);

    HttpHeaders headers = injected.getHeaders();
    assertNotNull(headers.get(ApolloAuditConstants.TRACE_ID));
    assertNotNull(headers.get(ApolloAuditConstants.SPAN_ID));
    assertNotNull(headers.get(ApolloAuditConstants.OPERATOR));
    assertNotNull(headers.get(ApolloAuditConstants.PARENT_ID));
    assertNotNull(headers.get(ApolloAuditConstants.FOLLOWS_FROM_ID));
  }