code: def test_union(self):
      u = self.s.union(self.items2)
      for c in self.letters:
          self.assertEqual(c in u, c in self.d or c in self.items2)
      self.assertEqual(self.s, WeakSet(self.items))
      self.assertEqual(type(u), WeakSet)
      self.assertRaises(TypeError, self.s.union, [[]])
      for C in set, frozenset, dict.fromkeys, list, tuple:
          x = WeakSet(self.items + self.items2)
          c = C(self.items2)
          self.assertEqual(self.s.union(c), x)
          del c
      self.assertEqual(len(u), len(self.items) + len(self.items2))
      self.items2.pop()
      gc.collect()
      self.assertEqual(len(u), len(self.items) + len(self.items2))
  
imports: import unittest
  from weakref import WeakSet
  import copy
  import string
  from collections import UserString
  from collections.abc import Set, MutableSet
  import gc
  import contextlib
  from test import support
label_desc: Use image node_id 6 for calling the TestWeakSet obj's underlying member method code with example usage: obj.test_union() without return types