code: def test_union_base(self, index):
      index = index.unique()
      first = index[3:]
      second = index[:5]
      everything = index
  
      union = first.union(second)
      tm.assert_index_equal(
          union.sort_values(), everything.sort_values()
      )
  
      if isinstance(index.dtype, DatetimeTZDtype):
          # The second.values below will drop tz, so the rest of this test
          #  is not applicable.
          return
  
      # GH#10149
      cases = [second.to_numpy(), second.to_series(), second.to_list()]
      for case in cases:
          result = first.union(case)
          assert equal_contents(result, everything)
  
      if isinstance(index, MultiIndex):
          msg = "other must be a MultiIndex or a list of tuples"
          with pytest.raises(TypeError, match=msg):
              first.union([1, 2, 3])
  
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 3 for calling the TestSetOps obj's underlying member method code with example usage: obj.test_union_base(index) without return types