code: public function preview($msgType, $message, $to, $by = self::PREVIEW_BY_OPENID)
      {
          $message = (new MessageBuilder())->msgType($msgType)->message($message)->to($to)->buildPreview($by);
  
          return $this->post(self::API_PREVIEW, $message);
      }
docs: Preview a message.
  
  @param string $msgType message type
  @param mixed  $message message
  @param string $to
  @param string $by
  
  @return mixed