code: def test_join_self(idx, join_type):
      result = idx.join(idx, how=join_type)
      expected = idx
      if join_type == "outer":
          expected = expected.sort_values()
      tm.assert_index_equal(result, expected)
  
file_path: pandas/pandas/tests/indexes/multi/test_join.py
imports: import numpy
  import pytest
  from pandas import DataFrame, Index, Interval, MultiIndex, Series, StringDtype
  import pandas._testing
label_desc: Use image node_id 3 for calling a global function with example usage: test_join_self(idx, join_type) without return types