code: public function find($out_trade_no = '')
      {
          $this->config['out_trade_no'] = $out_trade_no;
          $this->unsetTradeTypeAndNotifyUrl();
          return $this->getResult($this->gateway_query);
      }
docs: 查询订单状态
  @param string $out_trade_no
  @return array
  @throws GatewayException