Class RevRevBlocked

Lib/test/test_collections.py:1051–1052

        class RevItBlocked(Rev):
            __iter__ = None
        class RevRevBlocked(Rev):
            __reversed__ = None
        self.assertIsSubclass(Rev, Reversible)
        self.assertIsInstance(Rev(), Reversible)
        self.assertNotIsSubclass(RevItBlocked, Reversible)