'L{frozenset} should behave like the expected frozenset interface.'

def test_frozenset(self):

    a = frozenset(['a', 'b'])
    self.assertRaises(AttributeError, getattr, a, 'add')
    self.assertEqual(sorted(a), ['a', 'b'])
    b = frozenset(['r', 's'])
    d = a.union(b)
    b = list(d)
    b.sort()
    self.assertEqual(b, ['a', 'b', 'r', 's'])
