def METHOD_NAME(self):
    for iedge, (etrans, eref) in enumerate(self.ref.edges):
        for ichild, (ctrans, cref) in enumerate(eref.children):
            swapped_up = etrans.swapup(ctrans)
            self.assertNotEqual(swapped_up, None)
            ctrans_, etrans_ = swapped_up
            self.assertEqual(etrans * ctrans, ctrans_ * etrans_)
            swapped_down = etrans_.swapdown(ctrans_)
            self.assertEqual(swapped_down, (etrans, ctrans))