code: def test_combine_first_doc_example(self):
      # doc example
      df1 = DataFrame(
          {
              "A": [1.0, np.nan, 3.0, 5.0, np.nan],
              "B": [np.nan, 2.0, 3.0, np.nan, 6.0],
          }
      )
  
      df2 = DataFrame(
          {
              "A": [5.0, 2.0, 4.0, np.nan, 3.0, 7.0],
              "B": [np.nan, np.nan, 3.0, 4.0, 6.0, 8.0],
          }
      )
  
      result = df1.combine_first(df2)
      expected = DataFrame(
          {"A": [1, 2, 3, 5, 3, 7.0], "B": [np.nan, 2, 3, 4, 6, 8]}
      )
      tm.assert_frame_equal(result, expected)
  
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 5 for calling the TestDataFrameCombineFirst obj's underlying member method code with example usage: obj.test_combine_first_doc_example() without return types