code: def test_number_postal_code_normalization():
      df = pd.DataFrame({"postal_code": [103305, 111222]})
      dataset = Dataset("test321", df=df)  # type: ignore
      dataset.meaning_types = {
          "postal_code": FileColumnMeaningType.POSTAL_CODE
      }
      dataset._Dataset__normalize_postal_code()
      assert dataset.data.loc[0, "postal_code"] == "103305"
      assert dataset.data.loc[1, "postal_code"] == "111222"
  
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 18 for calling a global function with example usage: test_number_postal_code_normalization() without return types