code: def test_union_duplicate_index_different_dtypes():
      # GH#36289
      a = Index([1, 2, 2, 3])
      b = Index(["1", "0", "0"])
      expected = Index([1, 2, 2, 3, "1", "0", "0"])
      result = a.union(b, sort=False)
      tm.assert_index_equal(result, expected)
  
imports: from datetime import datetime
  import operator
  import numpy
  import pytest
  from pandas._libs import lib
  from pandas.core.dtypes.cast import find_common_type
  from pandas import CategoricalDtype, CategoricalIndex, DatetimeTZDtype, Index, MultiIndex, PeriodDtype, RangeIndex, Series, Timestamp
  import pandas._testing
  from pandas.api.types import is_signed_integer_dtype, pandas_dtype
label_desc: Use image node_id 13 for calling a global function with example usage: test_union_duplicate_index_different_dtypes() without return types