code: def test_prep_skl_df_coercion(copy_df):
      """Test that prep_skl_df behaves correctly on the coercion case."""
      mixed_example = pd.DataFrame({0: [1, 2, 3], "b": [1, 2, 3]})
  
      res = prep_skl_df(mixed_example, copy_df=copy_df)
  
      assert np.all(res.columns == ["0", "b"])
  
      if not copy_df:
          assert res is mixed_example
  
imports: import numpy
  import pandas
  import pytest
  from sktime.utils.sklearn._adapt_df import prep_skl_df
label_desc: Use image node_id 1 for calling a global function with example usage: test_prep_skl_df_coercion(copy_df) without return types