Class ItBlocked

Lib/test/test_collections.py:995–996

        class It:
            def __iter__(self): return iter([])
        class ItBlocked(It):
            __iter__ = None
        self.assertIsSubclass(It, Iterable)
        self.assertIsInstance(It(), Iterable)
        self.assertNotIsSubclass(ItBlocked, Iterable)