factory.go

// factory
package factory

import (
    "errors"
    "fmt"
)

const (
    Cash      = 1
    DebitCard = 2
)

type PaymentMethod interface {
    Pay(amount float32) string
}

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!", m))
    }
}

type CashPM struct{}
type DebitCardPM struct{}

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

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

factory_test.go

// factorymethod
package factory

import (
    "strings"
    "testing"
)

func TestGetPaymentMethodCash(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 doesn'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 doesn't correct")
    }
    t.Log("Log:", msg)
}

程序輸出如下，

image.png