code: def test_combine_first_mixed(self):
      a = Series(["a", "b"], index=range(2))
      b = Series(range(2), index=range(2))
      f = DataFrame({"A": a, "B": b})
  
      a = Series(["a", "b"], index=range(5, 7))
      b = Series(range(2), index=range(5, 7))
      g = DataFrame({"A": a, "B": b})
  
      exp = DataFrame(
          {"A": list("abab"), "B": [0, 1, 0, 1]}, index=[0, 1, 5, 6]
      )
      combined = f.combine_first(g)
      tm.assert_frame_equal(combined, exp)
  
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 1 for calling the TestDataFrameCombineFirst obj's underlying member method code with example usage: obj.test_combine_first_mixed() without return types