code: def test_fillna_downcast(self):
      # GH#15277
      # infer int64 from float64
      ser = Series([1.0, np.nan])
      msg = "The 'downcast' keyword in fillna is deprecated"
      with tm.assert_produces_warning(FutureWarning, match=msg):
          result = ser.fillna(0, downcast="infer")
      expected = Series([1, 0])
      tm.assert_series_equal(result, expected)
  
      # infer int64 from float64 when fillna value is a dict
      ser = Series([1.0, np.nan])
      with tm.assert_produces_warning(FutureWarning, match=msg):
          result = ser.fillna({1: 0}, downcast="infer")
      expected = Series([1, 0])
      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 9 for calling the TestSeriesFillNA obj's underlying member method code with example usage: obj.test_fillna_downcast() without return types