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tech/20210204 How to implement business requirements in software development.md
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[#]: collector: (lujun9972)
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[#]: translator: (toknow-gh)
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[#]: reviewer: ( )
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[#]: publisher: ( )
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[#]: url: ( )
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[#]: subject: (How to implement business requirements in software development)
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[#]: via: (https://opensource.com/article/21/2/exceptional-behavior)
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[#]: author: (Alex Bunardzic https://opensource.com/users/alex-bunardzic)
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How to implement business requirements in software development
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======
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Increment your e-commerce app to ensure it implements required business
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process rules correctly.
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![Working on a team, busy worklife][1]
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In my previous articles in this series, I explained why tackling coding problems all at once, as if they were hordes of zombies, is a mistake. I'm using a helpful acronym to explain why it's better to approach problems incrementally. **ZOMBIES** stands for:
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**Z** – Zero
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**O** – One
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**M** – Many (or more complex)
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**B** – Boundary behaviors
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**I** – Interface definition
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**E** – Exercise exceptional behavior
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**S** – Simple scenarios, simple solutions
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In the first three articles in this series, I demonstrated the first five **ZOMBIES** principles. The first article [implemented **Z**ero][2], which provides the simplest possible path through your code. The second article performed [tests with **O**ne and **M**any][3] samples, and the third article looked at [**B**oundaries and **I**nterfaces][4]. In this article, I'll take a look at the penultimate letter in our acronym: **E**, which stands for "exercise exceptional behavior."
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### Exceptional behavior in action
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When you write an app like the e-commerce tool in this example, you need to contact product owners or business sponsors to learn if there are any specific business policy rules that need to be implemented.
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Sure enough, as with any e-commerce operation, you want to put business policy rules in place to entice customers to keep buying. Suppose a business policy rule has been communicated that any order with a grand total greater than $500 gets a percentage discount.
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OK, time to roll up your sleeves and craft the executable expectation for this business policy rule:
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```
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[Fact]
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public void Add2ItemsTotal600GrandTotal540() {
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var expectedGrandTotal = 540.00;
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var actualGrandTotal = 0.00;
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Assert.Equal(expectedGrandTotal, actualGrandTotal);
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}
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```
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The confirmation example that encodes the business policy rule states that if the order total is $600.00, the `shoppingAPI` will calculate the grand total to discount it to $540.00. The script above fakes the expectation just to see it fail. Now, make it pass:
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```
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[Fact]
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public void Add2ItemsTotal600GrandTotal540() {
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var expectedGrandTotal = 540.00;
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Hashtable item = [new][5] Hashtable();
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item.Add("00000001", 200.00);
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shoppingAPI.AddItem(item);
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Hashtable item2 = [new][5] Hashtable();
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item2.Add("00000002", 400.00);
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shoppingAPI.AddItem(item2);
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var actualGrandTotal = shoppingAPI.CalculateGrandTotal();
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Assert.Equal(expectedGrandTotal, actualGrandTotal);
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}
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```
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In the confirmation example, you are adding one item priced at $200 and another item priced at $400 for a total of $600 for the order. When you call the `CalculateGrandTotal()` method, you expect to get a total of $540.
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Will this microtest pass?
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```
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[xUnit.net 00:00:00.57] tests.UnitTest1.Add2ItemsTotal600GrandTotal540 [FAIL]
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X tests.UnitTest1.Add2ItemsTotal600GrandTotal540 [2ms]
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Error Message:
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Assert.Equal() Failure
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Expected: 540
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Actual: 600
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[...]
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```
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Well, it fails miserably. You were expecting $540, but the system calculates $600. Why the error? It's because you haven't taught the system how to calculate the discount on order totals larger than $500 and then subtract that discount from the grand total.
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Implement that processing logic. Judging from the confirmation example above, when the order total is $600.00 (which is greater than the business rule threshold of an order totaling $500), the expected grand total is $540. This means the system needs to subtract $60 from the grand total. And $60 is precisely 10% of $600. So the business policy rule that deals with discounts expects a 10% discount on all order totals greater than $500.
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Implement this processing logic in the `ShippingAPI` class:
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```
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private double Calculate10PercentDiscount(double total) {
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double discount = 0.00;
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if(total > 500.00) {
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discount = (total/100) * 10;
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}
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return discount;
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}
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```
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First, check to see if the order total is greater than $500. If it is, then calculate 10% of the order total.
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You also need to teach the system how to subtract the calculated 10% from the order grand total. That's a very straightforward change:
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```
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`return grandTotal - Calculate10PercentDiscount(grandTotal);`
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```
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Now all tests pass, and you're again enjoying steady success. Your script **Exercises exceptional behavior** to implement the required business policy rules.
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### One more to go
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I've taken us to **ZOMBIE** now, so there's just **S** remaining. I'll cover that in the exciting series finale.
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--------------------------------------------------------------------------------
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via: https://opensource.com/article/21/2/exceptional-behavior
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作者：[Alex Bunardzic][a]
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选题：[lujun9972][b]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://opensource.com/users/alex-bunardzic
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[b]: https://github.com/lujun9972
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[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/team_dev_email_chat_video_work_wfm_desk_520.png?itok=6YtME4Hj (Working on a team, busy worklife)
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[2]: https://opensource.com/article/21/1/zombies-zero
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[3]: https://opensource.com/article/21/1/zombies-2-one-many
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[4]: https://opensource.com/article/21/1/zombies-3-boundaries-interface
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[5]: http://www.google.com/search?q=new+msdn.microsoft.com
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@ -0,0 +1,128 @@
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[#]: collector: (lujun9972)
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[#]: translator: (toknow-gh)
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[#]: reviewer: ( )
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[#]: publisher: ( )
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[#]: url: ( )
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[#]: subject: (How to implement business requirements in software development)
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[#]: via: (https://opensource.com/article/21/2/exceptional-behavior)
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[#]: author: (Alex Bunardzic https://opensource.com/users/alex-bunardzic)
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ZOMBIES：如何在软件开发中实现业务需求（四）
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======
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完善你的电商 app，使它能够正确处理业务规则。
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![Working on a team, busy worklife][1]
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在前面的文章中，我已经解释了为什么将编程问题看作一整群丧尸来处理是错误的。我用 ZOMBIES 方法来解释为什么循序渐进地处理问题更好。
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ZOMBIES 表示以下首字母缩写：
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**Z** – 最简场景（Zero）
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**O** – 单元素场景（One）
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**M** – 多元素场景（Many or more complex）
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**B** – 边界行为（Boundary behaviors）
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**I** – 接口定义（Interface definition）
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**E** – 处理特殊行为（Exercise exceptional behavior）
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**S** – 简单场景用简单的解决方案（Simple scenarios, simple solutions）
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在系列的前三篇文章中，我展示了 ZOMBIES 方法的前五项。第一篇中 [实现了最简场景][2]，它为代码提供了最简可行路径。第二篇文章中执行了 [单元素场景和多元素场景上的测试][3]。第三篇中介绍了[边界和接口][4]。在本文中，我将带你了解倒数第二个方法：处理特殊行为。
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### 处理特殊行为
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在开发一个电子购物应用时，你需要从产品负责人或赞助商那里了解需要采用什么销售策略。
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毫无疑问，与任何电子商业活动一样，你需要通过制定销售策略来诱导顾客进行消费。假设有如下的销售策略：订单金额超过 ￥500 时可以享受一定的折扣优惠。
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现在将这个销售策略转换为可运行期望：
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```
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[Fact]
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public void Add2ItemsTotal600GrandTotal540() {
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var expectedGrandTotal = 540.00;
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var actualGrandTotal = 0.00;
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Assert.Equal(expectedGrandTotal, actualGrandTotal);
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}
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```
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这个正面样例表示的销售策略是，如果订单总额为 ￥600.00，那么 `shoppingAPI` 会将其减价为 ￥540.00。上面的代码伪造了一个失败验证用例。现在修改它，让它能够通过测试：
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```
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[Fact]
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public void Add2ItemsTotal600GrandTotal540() {
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var expectedGrandTotal = 540.00;
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Hashtable item = [new][5] Hashtable();
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item.Add("00000001", 200.00);
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shoppingAPI.AddItem(item);
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Hashtable item2 = [new][5] Hashtable();
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item2.Add("00000002", 400.00);
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shoppingAPI.AddItem(item2);
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var actualGrandTotal = shoppingAPI.CalculateGrandTotal();
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Assert.Equal(expectedGrandTotal, actualGrandTotal);
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}
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```
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在这个正样例中，你向购物框加入一件价值 ￥200 的商品和一件价值 ￥400 的商品，使总价达到 ￥600 。当调用 `CalculateGrandTotal()` 方法时，你期望总价是 ￥540。
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这个微测试能够通过吗？
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```
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[xUnit.net 00:00:00.57] tests.UnitTest1.Add2ItemsTotal600GrandTotal540 [FAIL]
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X tests.UnitTest1.Add2ItemsTotal600GrandTotal540 [2ms]
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Error Message:
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Assert.Equal() Failure
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Expected: 540
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Actual: 600
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[...]
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```
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很可惜，它失败了。你期望的结果是 ￥540，但计算结果为 ￥600。为什么会这样呢？那是因为你还没有告诉系统在订单总价大于 ￥500 时怎么进行折扣计算。
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现在来实现折扣计算逻辑。根据上面的正样例可知，当订单总价为 ￥600（超过了营销策略的阈值 ￥500）时，期望的最终总价为 ￥540。也就是说系统需要从订单总额中减去 ￥60。刚好是是原订单总价的 10%。因此该销售规则就是当订单总额超过 ￥500 时享受九折优惠。
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在 `ShippingAPI` 类中实现该处理逻辑：
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```
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private double Calculate10PercentDiscount(double total) {
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double discount = 0.00;
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if(total > 500.00) {
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discount = (total/100) * 10;
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}
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return discount;
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}
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```
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首先，检查订单总额是否大于 ￥500 。如果是，则计算出总额的 10%。
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你还需要告诉系统怎么从订单总额中减去 10%。改动非常直接：
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```
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`return grandTotal - Calculate10PercentDiscount(grandTotal);`
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```
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到此，所有测试都能够通过。你又一次享受到系统处于稳态的欢愉。你的代码通过处理特殊行为实现了需要的销售策略。
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### 最后一步
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现在我已经介绍完 ZOMBIE 了，只剩下 S 了。我将会在最后一篇中介绍它。
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--------------------------------------------------------------------------------
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via: https://opensource.com/article/21/2/exceptional-behavior
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作者：[Alex Bunardzic][a]
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选题：[lujun9972][b]
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译者：[toknow-gh](https://github.com/toknow-gh)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://opensource.com/users/alex-bunardzic
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[b]: https://github.com/lujun9972
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[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/team_dev_email_chat_video_work_wfm_desk_520.png?itok=6YtME4Hj (Working on a team, busy worklife)
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[2]: https://opensource.com/article/21/1/zombies-zero
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[3]: https://opensource.com/article/21/1/zombies-2-one-many
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[4]: https://opensource.com/article/21/1/zombies-3-boundaries-interface
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[5]: http://www.google.com/search?q=new+msdn.microsoft.com
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