code: def test_fillna_datetime64_with_timezone_tzinfo(self):
      # https://github.com/pandas-dev/pandas/issues/38851
      # different tzinfos representing UTC treated as equal
      ser = Series(date_range("2020", periods=3, tz="UTC"))
      expected = ser.copy()
      ser[1] = NaT
      result = ser.fillna(datetime(2020, 1, 2, tzinfo=timezone.utc))
      tm.assert_series_equal(result, expected)
  
      # pre-2.0 we cast to object with mixed tzs, in 2.0 we retain dtype
      ts = Timestamp("2000-01-01", tz="US/Pacific")
      ser2 = Series(ser._values.tz_convert("dateutil/US/Pacific"))
      assert ser2.dtype.kind == "M"
      result = ser2.fillna(ts)
      expected = Series(
          [ser2[0], ts.tz_convert(ser2.dtype.tz), ser2[2]],
          dtype=ser2.dtype,
      )
      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 31 for calling the TestSeriesFillNA obj's underlying member method code with example usage: obj.test_fillna_datetime64_with_timezone_tzinfo() without return types