testing to see if the method returns an interface

gistfile1.txt

func (order Order) StoreTransactions() interface{} {  
		config, _ := config.LoadConfig(".")
	    var payment Payment
	    query := `INSERT INTO payments(amount, reference,payment_method,created_at) 
				  VALUES(@paymentAmount, @paymentReference, @paymentMethod, @paymentCreatedAt) return(id)`
		trans := pgx.NamedArgs{
				"paymentAmount": order.Total,
				"paymentReference": Random(20),
				"paymentMethod":    "Cash",
				"paymentCreatedAt" : time.Now(),
		}   
	    err := database.DB.QueryRow(context.Background(),query, trans).Scan(&payment.Id);
		if err != nil {
			panic("Could Execute this Query")
		}

        data := map[string]string{
            "req" : "card_payment",
			"currency" : "USD",
			"fname" : order.Customer.FirstName,
			"lname" : order.Customer.LastName,
            "encryption_key":config.DBENCRYPTION,
			"amount": strconv.FormatFloat(order.Total,'E',-1,64),
			"emailAddress" : order.Customer.Email,
			"call_back" : config.CALLBACKURL,
			"success_url": config.SUCCESSURL,
			"failure_url" : config.FAILUREURL,
			// "phone" : order.Customer.Phone,
			"description" : "payments",
			"txRef" : payment.Reference,
		}
		
        payload, _:= json.Marshal(data)        
		req, err := http.NewRequest("POST",config.PAYMENTURL,strings.NewReader(string(payload))) 
		if err !=nil{
           return err
		}
		req.Header.Add("Accept", "application/json")
		req.Header.Add("Content-Type", "application/json")
		resp, err := http.DefaultClient.Do(req)
		if err != nil {
			return err
		}

		var res map[string]interface{}
		if err := json.NewDecoder(resp.Body).Decode(&res); err!=nil {
            return err
		}
		return res
}