    def test_scroll(self):
        """
        Check that Scroll works.
        """
        # Check that it will attempt to scroll the screen at the required rate.
        screen = MagicMock(spec=Screen, colours=8, unicode_aware=False)
        effect = Scroll(screen, 2)
        effect.reset()
        effect.update(1)
        screen.scroll.assert_not_called()
        effect.update(2)
        screen.scroll.assert_called_once()

        # Check there is no stop frame
        self.assertEqual(effect.stop_frame, 0)

        # This effect should ignore events.
        event = object()
        self.assertEqual(event, effect.process_event(event))
Check that Scroll works.
tests/test_effects.py