def METHOD_NAME(self):
    import operator
    d = FixedKeysDict({'a':1, 'b':[3]})
    self.assertEqual(d['a'],1)
    self.assertEqual(d['b'],[3])
    self.assertRaises(AttributeError,operator.setitem,*(d,'a',2))
    d['b'].append(2)
    self.assertEqual(d['b'],[3,2])