code: def test_fillna_inplace(using_copy_on_write, downcast):
      df = DataFrame({"a": [1.5, np.nan], "b": 1})
      arr_a = get_array(df, "a")
      arr_b = get_array(df, "b")
  
      msg = "The 'downcast' keyword in fillna is deprecated"
      with tm.assert_produces_warning(FutureWarning, match=msg):
          df.fillna(5.5, inplace=True, downcast=downcast)
      assert np.shares_memory(get_array(df, "a"), arr_a)
      assert np.shares_memory(get_array(df, "b"), arr_b)
      if using_copy_on_write:
          assert df._mgr._has_no_reference(0)
          assert df._mgr._has_no_reference(1)
  
imports: import numpy
  import pytest
  from pandas import NA, ArrowDtype, DataFrame, Interval, NaT, Series, Timestamp, interval_range, option_context
  import pandas._testing
  from pandas.tests.copy_view.util import get_array
label_desc: Use image node_id 14 for calling a global function with example usage: test_fillna_inplace(using_copy_on_write, downcast) without return types