code: def test_corrwith_index_union(self):
      df1 = DataFrame(
          np.random.default_rng(2).random(size=(10, 2)),
          columns=["a", "b"],
      )
      df2 = DataFrame(
          np.random.default_rng(2).random(size=(10, 3)),
          columns=["a", "b", "c"],
      )
  
      result = df1.corrwith(df2, drop=False).index.sort_values()
      expected = df1.columns.union(df2.columns).sort_values()
      tm.assert_index_equal(result, expected)
  
imports: import numpy
  import pytest
  import pandas.util._test_decorators
  import pandas
  from pandas import DataFrame, Index, Series, date_range, isna
  import pandas._testing
label_desc: Use image node_id 7 for calling the TestDataFrameCorrWith obj's underlying member method code with example usage: obj.test_corrwith_index_union() without return types