code: def test_string_datetime_to_timestamp_convertion():
      df = pd.DataFrame(
          [
              {"date": "2020-01-01T00:00:00Z"},
          ]
      )
      df["date"] = pd.to_datetime(df.date)
      converter = DateTimeSearchKeyConverter("date")
      df = converter.convert(df)
      assert df.shape == (1, 1)
      assert df["date"].dtype == "Int64"
      assert df.loc[0, "date"] == 1577836800000
  
imports: import ipaddress
  import random
  from datetime import date, datetime
  import numpy
  import pandas
  import pytest
  from pandas.testing import assert_frame_equal
  from upgini import Dataset, FileColumnMeaningType
  from upgini.errors import ValidationError
  from upgini.metadata import ModelTaskType, SearchKey
  from upgini.resource_bundle import bundle
  from upgini.utils.datetime_utils import DateTimeSearchKeyConverter
  from upgini.utils.email_utils import EmailSearchKeyConverter
  from upgini.utils.features_validator import FeaturesValidator
  from upgini.utils.warning_counter import WarningCounter
label_desc: Use image node_id 8 for calling a global function with example usage: test_string_datetime_to_timestamp_convertion() without return types