docstr: boilerplate callback to simulate a client's `post()` method.
code: def post(self, msg):
      """boilerplate callback to simulate a client's `post()` method."""
      msg = json.loads(msg)
      assert msg["id"] is not None
  
imports: import json
  import time
  import numpy
  import pyarrow
  from datetime import datetime
  from functools import partial
  from pytest import raises
  from perspective import Table, PerspectiveError, PerspectiveManager
label_desc: Use image node_id 1 for calling the TestPerspectiveManager obj's underlying member method code with example usage: obj.post(msg) without return types