go语言设计模式之factory

factory.go

package factory

import (
	"errors"
	"fmt"
)

const (
	Cash      = 1
	DebitCard = 2
)

type PaymentMethod interface {
	Pay(amount float32) string
}

type CashPM struct{}
type DebitCardPM struct{}

func GetPaymentMethod(m int) (PaymentMethod, error) {
	switch m {
	case Cash:
		return new(CashPM), nil
	case DebitCard:
		return new(DebitCardPM), nil
	default:
		return nil, errors.New(fmt.Sprintf("Payment method %d not recognized\n", m))
	}

}

func (c *CashPM) Pay(amount float32) string {
	return fmt.Sprintf("%0.2f paid using cash\n", amount)
}

func (c *DebitCardPM) Pay(amount float32) string {
	return fmt.Sprintf("%#0.2f paid using debit card\n", amount)
}

　　

factory_test.go

package factory

import (
	"strings"
	"testing"
)

func TestCreatePaymentMethodCash(t *testing.T) {
	payment, err := GetPaymentMethod(Cash)
	if err != nil {
		t.Fatal("A payment method of type 'Cash' must exist.")
	}

	msg := payment.Pay(10.30)

	if !strings.Contains(msg, "paid using cash") {
		t.Error("The cash payment method message was't correct")
	}
	t.Log("LOG: ", msg)
}

func TestGetPaymentMethodDebitCard(t *testing.T) {
	payment, err := GetPaymentMethod(DebitCard)
	if err != nil {
		t.Fatal("A payment method of type 'DebitCard' must exist.")
	}

	msg := payment.Pay(22.30)

	if !strings.Contains(msg, "paid using debit card") {
		t.Error("The debit card payment method message was't correct")
	}
	t.Log("LOG: ", msg)
}

func TestGetPaymentMethodNonExistent(t *testing.T) {
	_, err := GetPaymentMethod(20)

	if err == nil {
		t.Error("A payment mothod with ID 20 must return an error")
	}
	t.Log("LOG:", err)
}