code: def test_get_dummies_duplicate_columns(self, df):
      # GH20839
      df.columns = ["A", "A", "A"]
      result = get_dummies(df).sort_index(axis=1)
  
      expected = DataFrame(
          [
              [1, True, False, True, False],
              [2, False, True, True, False],
              [3, True, False, False, True],
          ],
          columns=["A", "A_a", "A_b", "A_b", "A_c"],
      ).sort_index(axis=1)
  
      expected = expected.astype({"A": np.int64})
  
      tm.assert_frame_equal(result, expected)
  
imports: import re
  import unicodedata
  import numpy
  import pytest
  import pandas.util._test_decorators
  from pandas.core.dtypes.common import is_integer_dtype
  import pandas
  from pandas import ArrowDtype, Categorical, CategoricalDtype, CategoricalIndex, DataFrame, Index, RangeIndex, Series, SparseDtype, get_dummies
  import pandas._testing
  from pandas.core.arrays.sparse import SparseArray
label_desc: Use image node_id 34 for calling the TestGetDummies obj's underlying member method code with example usage: obj.test_get_dummies_duplicate_columns(df) without return types