def METHOD_NAME(self):
    # Verify that modifications made by leaf functions percolate up the
    # callstack.
    with swap_attr(builtins, "len", len):
        def bar():
            builtins.len = lambda x: 4
        def foo(modifier):
            l = []
            l.append(len(range(7)))
            modifier()
            l.append(len(range(7)))
            return l
        self.configure_func(foo, lambda: None)
        self.assertEqual(foo(bar), [7, 4])