Response getServices(String version) throws IOException {
    Response response = client.newCall(new Request.Builder()
      .url(url(server, "/api/" + version + "/services"))
      .build())
      .execute();
    assertSuccessful(response);
    return response;
  }
This POSTs a single span. Afterwards, we expect this trace in storage, and also the self-trace
of POSTing it.
zipkin-server/src/test/java/zipkin2/server/internal/brave/ITZipkinSelfTracing.java