code: def test_arrow_timestamp_conversion():
      """Test that arrow timestamp values are converted to ISO-8601 strings"""
      data = {
          "date": [datetime(2004, 8, 1), datetime(2004, 9, 1), None],
          "value": [102, 129, 139],
      }
      pa_table = pa.table(data)
  
      values = to_values(pa_table)
      expected_values = {
          "values": [
              {"date": "2004-08-01T00:00:00.000000", "value": 102},
              {"date": "2004-09-01T00:00:00.000000", "value": 129},
              {"date": None, "value": 139},
          ]
      }
      assert values == expected_values
  
file_path: altair/tests/utils/test_dataframe_interchange.py
imports: from datetime import datetime
  import pandas
  import pytest
  import sys
  import os
  from altair.utils.data import to_values
label_desc: Use image node_id 2 for calling a global function with example usage: test_arrow_timestamp_conversion() without return types