def METHOD_NAME(self):
    class X(Structure):
        _fields_ = [("a", c_char_p),
                    ("b", c_char_p)]
    x = X()
    self.assertEqual(x._objects, None)
    x.a = b"spam"
    x.b = b"foo"
    self.assertEqual(x._objects, {"0": b"spam", "1": b"foo"})