def test_parent(self):
        """
        The parent of the widget passed to L{ScrolledArea} is set to a new
        L{Viewport} created by the L{ScrolledArea} which itself has the
        L{ScrolledArea} instance as its parent.
        """
        widget = TextOutput()
        scrolled = ScrolledArea(widget)
        self.assertIs(widget.parent, scrolled._viewport)
        self.assertIs(scrolled._viewport.parent, scrolled)

        The parent of the widget passed to L{ScrolledArea} is set to a new
        L{Viewport} created by the L{ScrolledArea} which itself has the
        L{ScrolledArea} instance as its parent.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/conch/test/test_window.py