code: def test_ffill_missing_arguments():
      # GH 14955
      df = DataFrame({"a": [1, 2], "b": [1, 1]})
      msg = "DataFrameGroupBy.fillna is deprecated"
      with tm.assert_produces_warning(FutureWarning, match=msg):
          with pytest.raises(ValueError, match="Must specify a fill"):
              df.groupby("b").fillna()
  
file_path: pandas/pandas/tests/groupby/test_missing.py
imports: import numpy
  import pytest
  import pandas
  from pandas import DataFrame, Index, date_range
  import pandas._testing
label_desc: Use image node_id 3 for calling a global function with example usage: test_ffill_missing_arguments() without return types