def test_set(self):
        """
        L{set} should behave like the expected set interface.
        """
        a = set()
        a.add('b')
        a.add('c')
        a.add('a')
        b = list(a)
        b.sort()
        self.assertEqual(b, ['a', 'b', 'c'])
        a.remove('b')
        b = list(a)
        b.sort()
        self.assertEqual(b, ['a', 'c'])

        a.discard('d')

        b = set(['r', 's'])
        d = a.union(b)
        b = list(d)
        b.sort()
        self.assertEqual(b, ['a', 'c', 'r', 's'])

        L{set} should behave like the expected set interface.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_compat.py