code: def test_one_digit_postal_code(postal_code_dataframe):
      primitive = OneDigitPostalCode().get_function()
      for x in postal_code_dataframe:
          series = postal_code_dataframe[x]
          actual = to_pandas(primitive(series))
          expected = to_pandas(
              series.apply(
                  lambda t: str(t)[0] if pd.notna(t) else pd.NA
              ),
          )
          pd.testing.assert_series_equal(actual, expected)
  
imports: import pandas
  from featuretools.primitives.standard.transform.postal import OneDigitPostalCode, TwoDigitPostalCode
  from featuretools.tests.testing_utils.es_utils import to_pandas
label_desc: Use image node_id 1 for calling a global function with example usage: test_one_digit_postal_code(postal_code_dataframe) without return types