docstr: The conversion from `datetime` to a Unix timestamp should not
  alter the timestamp in any way if both are in local time.
code: def test_manager_to_dict_unix_timestamps_from_datetime(
      self, sentinel
  ):
      """The conversion from `datetime` to a Unix timestamp should not
      alter the timestamp in any way if both are in local time."""
      s = sentinel(False)
  
      timestamp_data = {"a": [1580515140000]}
  
      schema = {"a": datetime}
  
      def handle_to_dict(msg):
          s.set(True)
          message = json.loads(msg)
  
          assert message["data"] == timestamp_data
  
          # convert back
          ts = datetime.fromtimestamp(message["data"]["a"][0] / 1000)
  
          assert ts == datetime(2020, 1, 31, 23, 59)
  
      message = {
          "id": 1,
          "table_name": "table1",
          "view_name": "view1",
          "cmd": "view",
      }
      manager = PerspectiveManager()
  
      table = Table(schema)
      table.update(timestamp_data)
  
      manager.host_table("table1", table)
      manager._process(message, self.post)
      to_dict_message = {
          "id": 2,
          "name": "view1",
          "cmd": "view_method",
          "method": "to_dict",
      }
      manager._process(to_dict_message, handle_to_dict)
      assert s.get() is True
  
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 36 for calling the TestPerspectiveManager obj's underlying member method code with example usage: obj.test_manager_to_dict_unix_timestamps_from_datetime(sentinel) without return types