code: def test_combine_first_mixed_bug(self):
      idx = Index(["a", "b", "c", "e"])
      ser1 = Series([5.0, -9.0, 4.0, 100.0], index=idx)
      ser2 = Series(["a", "b", "c", "e"], index=idx)
      ser3 = Series([12, 4, 5, 97], index=idx)
  
      frame1 = DataFrame({"col0": ser1, "col2": ser2, "col3": ser3})
  
      idx = Index(["a", "b", "c", "f"])
      ser1 = Series([5.0, -9.0, 4.0, 100.0], index=idx)
      ser2 = Series(["a", "b", "c", "f"], index=idx)
      ser3 = Series([12, 4, 5, 97], index=idx)
  
      frame2 = DataFrame({"col1": ser1, "col2": ser2, "col5": ser3})
  
      combined = frame1.combine_first(frame2)
      assert len(combined.columns) == 5
  
imports: from datetime import datetime
  import numpy
  import pytest
  from pandas.core.dtypes.cast import find_common_type
  from pandas.core.dtypes.common import is_dtype_equal
  import pandas
  from pandas import DataFrame, Index, MultiIndex, Series
  import pandas._testing
label_desc: Use image node_id 3 for calling the TestDataFrameCombineFirst obj's underlying member method code with example usage: obj.test_combine_first_mixed_bug() without return types