code: def test_timedelta_fillna(self, frame_or_series, unit):
      # GH#3371
      ser = Series(
          [
              Timestamp("20130101"),
              Timestamp("20130101"),
              Timestamp("20130102"),
              Timestamp("20130103 9:01:01"),
          ],
          dtype=f"M8[{unit}]",
      )
      td = ser.diff()
      obj = frame_or_series(td).copy()
  
      # reg fillna
      result = obj.fillna(Timedelta(seconds=0))
      expected = Series(
          [
              timedelta(0),
              timedelta(0),
              timedelta(1),
              timedelta(days=1, seconds=9 * 3600 + 60 + 1),
          ],
          dtype=f"m8[{unit}]",
      )
      expected = frame_or_series(expected)
      tm.assert_equal(result, expected)
  
      # GH#45746 pre-1.? ints were interpreted as seconds.  then that was
      #  deprecated and changed to raise. In 2.0 it casts to common dtype,
      #  consistent with every other dtype's behavior
      res = obj.fillna(1)
      expected = obj.astype(object).fillna(1)
      tm.assert_equal(res, expected)
  
      result = obj.fillna(Timedelta(seconds=1))
      expected = Series(
          [
              timedelta(seconds=1),
              timedelta(0),
              timedelta(1),
              timedelta(days=1, seconds=9 * 3600 + 60 + 1),
          ],
          dtype=f"m8[{unit}]",
      )
      expected = frame_or_series(expected)
      tm.assert_equal(result, expected)
  
      result = obj.fillna(timedelta(days=1, seconds=1))
      expected = Series(
          [
              timedelta(days=1, seconds=1),
              timedelta(0),
              timedelta(1),
              timedelta(days=1, seconds=9 * 3600 + 60 + 1),
          ],
          dtype=f"m8[{unit}]",
      )
      expected = frame_or_series(expected)
      tm.assert_equal(result, expected)
  
      result = obj.fillna(np.timedelta64(10**9))
      expected = Series(
          [
              timedelta(seconds=1),
              timedelta(0),
              timedelta(1),
              timedelta(days=1, seconds=9 * 3600 + 60 + 1),
          ],
          dtype=f"m8[{unit}]",
      )
      expected = frame_or_series(expected)
      tm.assert_equal(result, expected)
  
      result = obj.fillna(NaT)
      expected = Series(
          [
              NaT,
              timedelta(0),
              timedelta(1),
              timedelta(days=1, seconds=9 * 3600 + 60 + 1),
          ],
          dtype=f"m8[{unit}]",
      )
      expected = frame_or_series(expected)
      tm.assert_equal(result, expected)
  
      # ffill
      td[2] = np.nan
      obj = frame_or_series(td).copy()
      result = obj.ffill()
      expected = td.fillna(Timedelta(seconds=0))
      expected[0] = np.nan
      expected = frame_or_series(expected)
  
      tm.assert_equal(result, expected)
  
      # bfill
      td[2] = np.nan
      obj = frame_or_series(td)
      result = obj.bfill()
      expected = td.fillna(Timedelta(seconds=0))
      expected[2] = timedelta(days=1, seconds=9 * 3600 + 60 + 1)
      expected = frame_or_series(expected)
      tm.assert_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 11 for calling the TestSeriesFillNA obj's underlying member method code with example usage: obj.test_timedelta_fillna(frame_or_series, unit) without return types