basketCalculation.test.ts

describe('Unit | Basket price calculation', () => {
    let getBasketInformation: GetBasketInformation
    let addToBasket: AddToBasket

    beforeEach(() => {
        const basketRepository = new InMemoryBasketRepository()

        getBasketInformation = new GetBasketInformation(basketRepository)
        addToBasket          = new AddToBasket(basketRepository)
    })

    it('For an empty basket', async () => {
        const basket = await getBasketInformation.handle()

        expect(basket.price).to.equal(0)
        expect(basket.items).to.deep.equal([])
    })

    describe('Borrowing n different books', () => {
        it('Apply no discount', () => {
            await addToBasket.execute(new Book('1'))
            await addToBasket.execute(new Book('2'))
            await addToBasket.execute(new Book('3'))
            await addToBasket.execute(new Book('5'))

            const basket = await getBasketInformation.handle()

            expect(basket.price).to.equal(32)
            expect(basket.items).to.deep.equal([
                new Book('1'),
                new Book('2'),
                new Book('3'),
                new Book('5')
            ])
        })
    })

    describe('Borrowing n times the same book', () => {
        const book = new Book('1')

        it('Apply no discount for only one book', async () => {
            await addNTimesTheSameBook(1)

            const basket = await getBasketInformation.handle()

            expect(basket.price).to.equal(8)
            expect(basket.items).to.deep.equal([book])
        })

        it('Apply 5% discount for two same books', async () => {
            await addNTimesTheSameBook(2)

            const basket = await getBasketInformation.handle()

            expect(basket.price).to.equal(15.2)
            expect(basket.items).to.deep.equal([book, book])
        })

        it('Apply 25% discount for three same books', async () => {
            await addNTimesTheSameBook(3)

            const basket = await getBasketInformation.handle()

            expect(basket.price).to.equal(18)
            expect(basket.items).to.deep.equal([book, book, book])
        })

        it('Apply 25% discount for more than three times', async () => {
            await addNTimesTheSameBook(4)

            const basket = await getBasketInformation.handle()

            expect(basket.price).to.equal(24)
            expect(basket.items).to.deep.equal([book, book, book, book])
        })

        async function addNTimesTheSameBook(nTimes: number) {
            for (let i = 1; i <= nTimes; i++)
                await addToBasket.execute(book)
        }
    })
})