code: def test_datetime64_fillna(self):
      ser = Series(
          [
              Timestamp("20130101"),
              Timestamp("20130101"),
              Timestamp("20130102"),
              Timestamp("20130103 9:01:01"),
          ]
      )
      ser[2] = np.nan
  
      # ffill
      result = ser.ffill()
      expected = Series(
          [
              Timestamp("20130101"),
              Timestamp("20130101"),
              Timestamp("20130101"),
              Timestamp("20130103 9:01:01"),
          ]
      )
      tm.assert_series_equal(result, expected)
  
      # bfill
      result = ser.bfill()
      expected = Series(
          [
              Timestamp("20130101"),
              Timestamp("20130101"),
              Timestamp("20130103 9:01:01"),
              Timestamp("20130103 9:01:01"),
          ]
      )
      tm.assert_series_equal(result, expected)
  
imports: from datetime import datetime, timedelta, timezone
  import numpy
  import pytest
  import pytz
  from pandas import Categorical, DataFrame, DatetimeIndex, NaT, Period, Series, Timedelta, Timestamp, date_range, isna, timedelta_range
  import pandas._testing
  from pandas.core.arrays import period_array
label_desc: Use image node_id 12 for calling the TestSeriesFillNA obj's underlying member method code with example usage: obj.test_datetime64_fillna() without return types