code: def test_fillna_downcast_dict(self):
      # GH#40809
      df = DataFrame({"col1": [1, np.nan]})
  
      msg = "The 'downcast' keyword in fillna"
      with tm.assert_produces_warning(FutureWarning, match=msg):
          result = df.fillna({"col1": 2}, downcast={"col1": "int64"})
      expected = DataFrame({"col1": [1, 2]})
      tm.assert_frame_equal(result, expected)
  
imports: import numpy
  import pytest
  from pandas._config import using_pyarrow_string_dtype
  from pandas import Categorical, DataFrame, DatetimeIndex, NaT, PeriodIndex, Series, TimedeltaIndex, Timestamp, date_range, to_datetime
  import pandas._testing
  from pandas.tests.frame.common import _check_mixed_float
label_desc: Use image node_id 36 for calling the TestFillNA obj's underlying member method code with example usage: obj.test_fillna_downcast_dict() without return types