code: def test_join_mixed_non_unique_index(self):
      # GH 12814, unorderable types in py3 with a non-unique index
      df1 = DataFrame({"a": [1, 2, 3, 4]}, index=[1, 2, 3, "a"])
      df2 = DataFrame({"b": [5, 6, 7, 8]}, index=[1, 3, 3, 4])
      result = df1.join(df2)
      expected = DataFrame(
          {"a": [1, 2, 3, 3, 4], "b": [5, np.nan, 6, 7, np.nan]},
          index=[1, 2, 3, 3, "a"],
      )
      tm.assert_frame_equal(result, expected)
  
      df3 = DataFrame({"a": [1, 2, 3, 4]}, index=[1, 2, 2, "a"])
      df4 = DataFrame({"b": [5, 6, 7, 8]}, index=[1, 2, 3, 4])
      result = df3.join(df4)
      expected = DataFrame(
          {"a": [1, 2, 3, 4], "b": [5, 6, 6, np.nan]},
          index=[1, 2, 2, "a"],
      )
      tm.assert_frame_equal(result, expected)
  
imports: import re
  import numpy
  import pytest
  import pandas.util._test_decorators
  import pandas
  from pandas import Categorical, DataFrame, Index, MultiIndex, Series, Timestamp, bdate_range, concat, merge, option_context
  import pandas._testing
label_desc: Use image node_id 31 for calling the TestJoin obj's underlying member method code with example usage: obj.test_join_mixed_non_unique_index() without return types