def METHOD_NAME(self):
    self.order.action_confirm()
    self.assertEqual(self.order.picking_ids.delivery_zone_id, self.delivery_zone_a)
    self.order.picking_ids.delivery_zone_id = self.delivery_zone_b
    self.assertEqual(self.order.delivery_zone_id, self.delivery_zone_b)
    self.order.delivery_zone_id = self.delivery_zone_a
    self.assertEqual(self.order.picking_ids.delivery_zone_id, self.delivery_zone_a)