code: def test_join_with_categorical_index(self):
      # GH47812
      ix = ["a", "b"]
      id1 = pd.CategoricalIndex(ix, categories=ix)
      id2 = pd.CategoricalIndex(reversed(ix), categories=reversed(ix))
  
      df1 = DataFrame({"c1": ix}, index=id1)
      df2 = DataFrame({"c2": reversed(ix)}, index=id2)
      result = df1.join(df2)
      expected = DataFrame(
          {"c1": ["a", "b"], "c2": ["a", "b"]},
          index=pd.CategoricalIndex(["a", "b"], categories=["a", "b"]),
      )
      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 40 for calling the TestJoin obj's underlying member method code with example usage: obj.test_join_with_categorical_index() without return types