编辑“︁JavaScript BDD行为驱动开发”︁（章节）

== 实际应用案例 ==
=== 案例：电子商务购物车 ===
需求描述：
* 用户添加商品到购物车后，总价应自动更新。
* 如果商品数量为0，应从购物车移除。

'''BDD测试描述'''：
<syntaxhighlight lang="gherkin">
Feature: Shopping Cart
  Scenario: Add item to cart
    Given an empty shopping cart
    When user adds 2 units of "Product A" priced at $10 each
    Then the cart total should be $20

  Scenario: Remove item when quantity is zero
    Given a cart containing 1 unit of "Product B"
    When user updates quantity to 0
    Then "Product B" should be removed from cart
</syntaxhighlight>

'''JavaScript实现'''（使用Mocha + Chai）：
<syntaxhighlight lang="javascript">
const { expect } = require('chai');

class ShoppingCart {
  constructor() {
    this.items = [];
  }
  addItem(product, quantity, price) {
    this.items.push({ product, quantity, price });
  }
  updateQuantity(product, newQuantity) {
    const item = this.items.find(i => i.product === product);
    if (newQuantity <= 0) {
      this.items = this.items.filter(i => i.product !== product);
    } else {
      item.quantity = newQuantity;
    }
  }
  getTotal() {
    return this.items.reduce((sum, item) => sum + (item.quantity * item.price), 0);
  }
}

describe('ShoppingCart', () => {
  let cart;
  beforeEach(() => { cart = new ShoppingCart(); });

  it('should calculate total when adding items', () => {
    cart.addItem('Product A', 2, 10);
    expect(cart.getTotal()).to.equal(20);
  });

  it('should remove item when quantity is zero', () => {
    cart.addItem('Product B', 1, 15);
    cart.updateQuantity('Product B', 0);
    expect(cart.items).to.have.lengthOf(0);
  });
});
</syntaxhighlight>