code: def test_union(self, index, sort):
      first = index[5:20]
      second = index[:10]
      everything = index[:20]
  
      union = first.union(second, sort=sort)
      if sort in (None, False):
          tm.assert_index_equal(
              union.sort_values(), everything.sort_values()
          )
      else:
          tm.assert_index_equal(union, everything)
  
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 6 for calling the TestSetOpsUnsorted obj's underlying member method code with example usage: obj.test_union(index, sort) without return types