campus-errand/miniapp/stores/cart.test.js

/**
 * Property 7: 购物车数量与价格不变量
 *
 * 对于任意购物车状态：
 * - 总数量 = 所有菜品数量之和
 * - 总价 = 所有菜品的（数量 × 单价）之和
 * - 添加菜品使数量 +1
 * - 减少菜品使数量 -1，减至 0 时移除
 */
import { describe, it, expect } from 'vitest'
import * as fc from 'fast-check'

// ==================== 纯函数购物车逻辑（与 store 一致） ====================

/**
 * 计算购物车总数量
 * @param {Array} items - [{ dish, quantity }]
 */
function calcTotalCount(items) {
	return items.reduce((sum, item) => sum + item.quantity, 0)
}

/**
 * 计算购物车总价
 * @param {Array} items - [{ dish: { price }, quantity }]
 */
function calcTotalPrice(items) {
	return items.reduce((sum, item) => sum + item.quantity * item.dish.price, 0)
}

/**
 * 添加菜品，数量 +1
 */
function addItem(items, dish) {
	const copy = items.map(i => ({ dish: { ...i.dish }, quantity: i.quantity }))
	const existing = copy.find(i => i.dish.id === dish.id)
	if (existing) {
		existing.quantity += 1
	} else {
		copy.push({ dish: { ...dish }, quantity: 1 })
	}
	return copy
}

/**
 * 减少菜品，数量 -1，减至 0 时移除
 */
function removeItem(items, dishId) {
	const copy = items.map(i => ({ dish: { ...i.dish }, quantity: i.quantity }))
	const index = copy.findIndex(i => i.dish.id === dishId)
	if (index === -1) return copy
	copy[index].quantity -= 1
	if (copy[index].quantity <= 0) {
		copy.splice(index, 1)
	}
	return copy
}

// ==================== 生成器 ====================

/** 生成合法菜品对象 */
const dishArb = fc.record({
	id: fc.integer({ min: 1, max: 1000 }),
	name: fc.string({ minLength: 1, maxLength: 10 }),
	photo: fc.constant('test.png'),
	price: fc.float({ min: Math.fround(0.01), max: Math.fround(999), noNaN: true }).map(v => Math.round(v * 100) / 100)
})

/** 生成购物车操作序列 */
const cartActionArb = fc.oneof(
	dishArb.map(dish => ({ type: 'add', dish })),
	fc.integer({ min: 1, max: 1000 }).map(id => ({ type: 'remove', dishId: id }))
)

// ==================== 属性测试 ====================

describe('Feature: login-and-homepage, Property 7: 购物车数量与价格不变量', () => {
	/**
	 *
	 * 总数量始终等于所有菜品数量之和
	 */
	it('总数量等于所有菜品数量之和', () => {
		fc.assert(
			fc.property(
				fc.array(cartActionArb, { minLength: 1, maxLength: 50 }),
				(actions) => {
					let items = []
					for (const action of actions) {
						if (action.type === 'add') {
							items = addItem(items, action.dish)
						} else {
							items = removeItem(items, action.dishId)
						}
					}
					const expectedCount = items.reduce((s, i) => s + i.quantity, 0)
					expect(calcTotalCount(items)).toBe(expectedCount)
				}
			),
			{ numRuns: 200 }
		)
	})

	/**
	 *
	 * 总价始终等于所有菜品的（数量 × 单价）之和
	 */
	it('总价等于所有菜品的数量乘以单价之和', () => {
		fc.assert(
			fc.property(
				fc.array(cartActionArb, { minLength: 1, maxLength: 50 }),
				(actions) => {
					let items = []
					for (const action of actions) {
						if (action.type === 'add') {
							items = addItem(items, action.dish)
						} else {
							items = removeItem(items, action.dishId)
						}
					}
					const expectedPrice = items.reduce((s, i) => s + i.quantity * i.dish.price, 0)
					// 浮点精度容差
					expect(Math.abs(calcTotalPrice(items) - expectedPrice)).toBeLessThan(0.001)
				}
			),
			{ numRuns: 200 }
		)
	})

	/**
	 *
	 * 添加菜品使该菜品数量 +1
	 */
	it('添加菜品使数量加1', () => {
		fc.assert(
			fc.property(
				fc.array(cartActionArb, { maxLength: 20 }),
				dishArb,
				(setupActions, dish) => {
					let items = []
					for (const action of setupActions) {
						if (action.type === 'add') {
							items = addItem(items, action.dish)
						} else {
							items = removeItem(items, action.dishId)
						}
					}
					const beforeQty = items.find(i => i.dish.id === dish.id)?.quantity || 0
					const afterItems = addItem(items, dish)
					const afterQty = afterItems.find(i => i.dish.id === dish.id)?.quantity || 0
					expect(afterQty).toBe(beforeQty + 1)
				}
			),
			{ numRuns: 200 }
		)
	})

	/**
	 *
	 * 减少菜品使数量 -1，减至 0 时移除
	 */
	it('减少菜品使数量减1且减至0时移除', () => {
		fc.assert(
			fc.property(
				dishArb,
				fc.integer({ min: 1, max: 10 }),
				(dish, addCount) => {
					// 先添加若干次
					let items = []
					for (let i = 0; i < addCount; i++) {
						items = addItem(items, dish)
					}
					expect(items.find(i => i.dish.id === dish.id)?.quantity).toBe(addCount)

					// 减少一次
					const afterItems = removeItem(items, dish.id)
					if (addCount === 1) {
						// 减至 0，应被移除
						expect(afterItems.find(i => i.dish.id === dish.id)).toBeUndefined()
					} else {
						expect(afterItems.find(i => i.dish.id === dish.id)?.quantity).toBe(addCount - 1)
					}
				}
			),
			{ numRuns: 200 }
		)
	})
})