def add_stock(self, product_id, sku_info, quantity):
        """
        增加库存

        :param product_id: 商品ID
        :param sku_info: sku信息,格式"id1:vid1;id2:vid2",如商品为统一规格，则此处赋值为空字符串即可
        :param quantity: 增加的库存数量
        :return: 返回的 JSON 数据包
        """
        return self._post(
            'merchant/stock/add',
            data={
                "product_id": product_id,
                "sku_info": sku_info,
                "quantity": quantity
            }
        )