《重构》C#版实现（一）构建参考结果的测试用例

首先，列出的是第一个“电影租赁”案例的C#版初始代码：

using System;
using System.Collections.Generic;

namespace CH01_MovieRentalHouse
{
    public class Movie
    {
        public const int CHILDRENS = 2;
        public const int REGULAR = 0;
        public const int NEW_RELEASE = 1;

        public string Title { get; private set; }
        public int PriceCode { get; private set; }
        
        public Movie(string title, int priceCode)
        {
            Title = title;
            PriceCode = priceCode;
        }
    }

    public class Rental
    {
        public Movie Movie { get; private set; }
        public int DaysRented { get; private set; }

        public Rental(Movie rented, int days)
        {
            Movie = rented;
            DaysRented = days;
        }
    }

    public class Customer
    {
        public string Name { get; private set; }

        private List<Rental> Rentals = new List<Rental>();

        public Customer(string name)
        {
            Name = name;
        }

        public void Add(Rental rental)
        {
            Rentals.Add(rental);
        }

        public string Statement()
        {
            double totalAmount = 0;
            int frequentRenterPoints = 0;
            string result = "Rental Record for " + Name + "\n";
            foreach (Rental rental in Rentals)
            {
                double thisAmount = 0;
                
                // determine amounts for each line
                switch (rental.Movie.PriceCode)
                {
                    case Movie.REGULAR:
                        thisAmount += 2;
                        if (rental.DaysRented > 2)
                            thisAmount += (rental.DaysRented - 2) * 1.5;
                        break;
                    case Movie.NEW_RELEASE:
                        thisAmount += rental.DaysRented * 3;
                        break;
                    case Movie.CHILDRENS:
                        thisAmount += 1.5;
                        if (rental.DaysRented > 3)
                            thisAmount += (rental.DaysRented - 3) * 1.5;
                        break;
                }

                // add frequent renter points
                frequentRenterPoints++;
                // add bonus for a two day new release rental
                if (rental.Movie.PriceCode == Movie.NEW_RELEASE &&
                    rental.DaysRented > 1) frequentRenterPoints++;
                
                // show figures for this rental
                result += "\t" + rental.Movie.Title + "\t" + thisAmount.ToString() + "\n";
                totalAmount += thisAmount;
            }
            // add footer lines
            result += "Amount owed is " + totalAmount.ToString() + "\n";
            result += "You earned " + frequentRenterPoints.ToString() + " frequent renter points";
            return result;
        }
    }
}

　　在工作中，经常见到动辄数百，甚至上千行的方法。对于那些程序员们，我实在不知道他们拥有怎样的技巧，才能工作在复杂如斯的代码谜团中，同时还能（真的能么？）保证代码不出错。以个人经验及数据来说，结构良好的代码中，类方法的长度约有40%为1-5行，50%为5到15行左右，还有10%为15-50行。虽然不能严格地说方法的代码行数越少越好，但简短且职责更单一的方法确实成为了我衡量代码的重要标准之一。

　　《重构》一书中提到了一个重要概念：“每当我要进行重构的时候，第一个步骤永远相同：我得为即将修改的代码建立一组可靠的测试环境”。诚然，没有测试也能进行重构，但没有它的保障，大多数重构行为都会以失败告终。所以，后面所有的重构，都会在C#的单元测试框架基础上完成，而这也是《重构》中没有给出的部分（相当重要的部分）。
　　首先，必须确定的是初始代码的正确性，这是重构的基础之一，如果原始代码不正确，我们也就无法用它来得到可供参考的结果。那么，第一步工作不是立刻大刀阔斧地对现有代码进行重构，而是先使用正确的初始代码运行几分测试数据，得到相应的结果。为此，添加如下代码：

    class Program
    {
        static void Main(string[] args)
        {
            Movie braveHeart = new Movie("BraveHeart", Movie.NEW_RELEASE);
            Movie godFather = new Movie("GodFather", Movie.REGULAR);
            Movie wallE = new Movie("Wall-E", Movie.CHILDRENS);

            Rental bh4DayRental = new Rental(braveHeart, 4);
            Rental bh2DRental = new Rental(braveHeart, 2);
            Rental we7DRental = new Rental(wallE, 7);
            Rental gfRental = new Rental(godFather, 5);
            Rental we3DRental = new Rental(wallE, 3);

            Customer Charles = new Customer("Charles");
            Charles.Add(bh4DayRental);
            Charles.Add(gfRental);

            Customer Jess = new Customer("Jess");
            Jess.Add(bh4DayRental);
            Jess.Add(we7DRental);
            Jess.Add(bh2DRental);

            Customer Rebecca = new Customer("Rebecca");
            Rebecca.Add(we7DRental);
            Rebecca.Add(we3DRental);

            Customer Lucas = new Customer("Lucas");
            Lucas.Add(bh2DRental);
            Lucas.Add(we7DRental);
            Lucas.Add(we3DRental);

            Console.WriteLine(Charles.Statement());
            Console.WriteLine(Jess.Statement());
            Console.WriteLine(Rebecca.Statement());
            Console.WriteLine(Lucas.Statement());
        }
    }

　　 运行后，控制台输出如下：

　　接着，我们要做的就是在这个数据的基础上编写测试用例。鉴于有些同学可能还不知道怎么使用C#的单元测试框架，所以演示一次，后面若无特殊情况，一概略过。关于C#单元测试的更多使用方法，参见微软的教程，或在google上搜索。

http://msdn.microsoft.com/zh-cn/library/ms379625(v=vs.80).aspx

　　1.在Statement方法上点击鼠标右键，会出现如下菜单（因为我装了VA插件，所以菜单可能不完全一致）

　　2.选中其中的创建单元测试，会出现下述对话框

　　3.选中待测试的Statement()方法后，点击确定

　　4.在项目名称一栏，输入一个你喜欢的名字作为测试项目的名称，在这里我将测试项目命名为：Tests，然后创建该项目。解决方案中多出了下图中的文件和工程

　　5.打开CustomerTest.cs文件，发现系统自动为我们添加了一个测试：

        /// <summary>
        ///Statement 的测试
        ///</summary>
        [TestMethod()]
        public void StatementTest()
        {
            string name = string.Empty; // TODO: 初始化为适当的值
            Customer target = new Customer(name); // TODO: 初始化为适当的值
            string expected = string.Empty; // TODO: 初始化为适当的值
            string actual;
            actual = target.Statement();
            Assert.AreEqual(expected, actual);
            Assert.Inconclusive("验证此测试方法的正确性。");
        }

该测试没什么用处，我们要做的是清空它，并使用前面产生的标准数据来编写第一个测试，结果参照如下：

        [TestMethod()]
        public void StatementForCharles()
        {
            Movie braveHeart = new Movie("BraveHeart", Movie.NEW_RELEASE);
            Movie godFather = new Movie("GodFather", Movie.REGULAR);
            Movie wallE = new Movie("Wall-E", Movie.CHILDRENS);

            Rental bh4DayRental = new Rental(braveHeart, 4);
            Rental bh2DRental = new Rental(braveHeart, 2);
            Rental we7DRental = new Rental(wallE, 7);
            Rental gfRental = new Rental(godFather, 5);
            Rental we3DRental = new Rental(wallE, 3);

            Customer charles = new Customer("Charles");
            charles.Add(bh4DayRental);
            charles.Add(gfRental);

            string expected = "Rental Record for Charles\n"
                            + "\tBraveHeart\t12\n"
                            + "\tGodFather\t6.5\n"
                            + "Amount owed is 18.5\n"
                            + "You earned 3 frequent renter points";

            Assert.AreEqual(expected, charles.Statement());
        }

　　需要注意的是，该测试的部分代码是直接copy自上面Main函数，虽然这（拷贝、粘贴）不是被推荐的行为，但我们最终的目的实际上是将原来Main中的人工测试搬移到自动测试中，所以是可以被接受的，毕竟搬移后没有功能重复的代码。

　　6.构造完该测试后，从下图所示菜单中 运行 单元测试

　　短暂的编译、运行后，IDE中出现了类似下面的结果窗口：

　　结果列中，绿色的小勾勾说明，我们的测试通过了，如果输入有误，则结果画面如下：

　　7.初步了解怎样添加自动测试后，我们接着为另外三个参考数据编写相应的测试用例，代码如下：

        [TestMethod()]
        public void StatementForJess()
        {
            Movie braveHeart = new Movie("BraveHeart", Movie.NEW_RELEASE);
            Movie godFather = new Movie("GodFather", Movie.REGULAR);
            Movie wallE = new Movie("Wall-E", Movie.CHILDRENS);

            Rental bh4DayRental = new Rental(braveHeart, 4);
            Rental bh2DRental = new Rental(braveHeart, 2);
            Rental we7DRental = new Rental(wallE, 7);
            Rental gfRental = new Rental(godFather, 5);
            Rental we3DRental = new Rental(wallE, 3);

            Customer jess = new Customer("Jess");
            jess.Add(bh4DayRental);
            jess.Add(we7DRental);
            jess.Add(bh2DRental);

            string expected = "Rental Record for Jess\n"
                            + "\tBraveHeart\t12\n"
                            + "\tWall-E\t7.5\n"
                            + "\tBraveHeart\t6\n"
                            + "Amount owed is 25.5\n"
                            + "You earned 5 frequent renter points";

            Assert.AreEqual(expected, jess.Statement());
        }

        [TestMethod()]
        public void StatementForRebecca()
        {
            Movie braveHeart = new Movie("BraveHeart", Movie.NEW_RELEASE);
            Movie godFather = new Movie("GodFather", Movie.REGULAR);
            Movie wallE = new Movie("Wall-E", Movie.CHILDRENS);

            Rental bh4DayRental = new Rental(braveHeart, 4);
            Rental bh2DRental = new Rental(braveHeart, 2);
            Rental we7DRental = new Rental(wallE, 7);
            Rental gfRental = new Rental(godFather, 5);
            Rental we3DRental = new Rental(wallE, 3);

            Customer rebecca = new Customer("Rebecca");
            rebecca.Add(we7DRental);
            rebecca.Add(we3DRental);

            string expected = "Rental Record for Rebecca\n"
                            + "\tWall-E\t7.5\n"
                            + "\tWall-E\t1.5\n"
                            + "Amount owed is 9\n"
                            + "You earned 2 frequent renter points";

            Assert.AreEqual(expected, rebecca.Statement());
        }

        [TestMethod()]
        public void StatementForLucas()
        {
            Movie braveHeart = new Movie("BraveHeart", Movie.NEW_RELEASE);
            Movie godFather = new Movie("GodFather", Movie.REGULAR);
            Movie wallE = new Movie("Wall-E", Movie.CHILDRENS);

            Rental bh4DayRental = new Rental(braveHeart, 4);
            Rental bh2DRental = new Rental(braveHeart, 2);
            Rental we7DRental = new Rental(wallE, 7);
            Rental gfRental = new Rental(godFather, 5);
            Rental we3DRental = new Rental(wallE, 3);

            Customer lucas = new Customer("Lucas");
            lucas.Add(bh2DRental);
            lucas.Add(we7DRental);
            lucas.Add(we3DRental);

            string expected = "Rental Record for Lucas\n"
                            + "\tBraveHeart\t6\n"
                            + "\tWall-E\t7.5\n"
                            + "\tWall-E\t1.5\n"
                            + "Amount owed is 15\n"
                            + "You earned 4 frequent renter points";

            Assert.AreEqual(expected, lucas.Statement());
        }

　　8.虽然测试都完成了，但是每一个测试中，有相当多的关于创建Movie和Rental对象的重复代码。本着“测试代码也要保持整洁”的原则，在这一篇的最后，我们把这些重复的可共享代码全部抽取为测试类的字段，得到完整的测试代码如下：

using CH01_MovieRentalHouse;
using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace Tests
{
    [TestClass]
    public class CustomerTest
    {
        private Movie braveHeart;
        private Movie godFather;
        private Movie wallE;
        private Rental bh4DayRental;
        private Rental bh2DRental;
        private Rental we7DRental;
        private Rental gfRental;
        private Rental we3DRental;

        public CustomerTest()
        {
            braveHeart = new Movie("BraveHeart", Movie.NEW_RELEASE);
            godFather = new Movie("GodFather", Movie.REGULAR);
            wallE = new Movie("Wall-E", Movie.CHILDRENS);

            bh4DayRental = new Rental(braveHeart, 4);
            bh2DRental = new Rental(braveHeart, 2);
            we7DRental = new Rental(wallE, 7);
            gfRental = new Rental(godFather, 5);
            we3DRental = new Rental(wallE, 3);
        }

        [TestMethod]
        public void StatementForCharles()
        {
            Customer charles = new Customer("Charles");
            charles.Add(bh4DayRental);
            charles.Add(gfRental);

            string expected = "Rental Record for Charles\n"
                            + "\tBraveHeart\t12\n"
                            + "\tGodFather\t6.5\n"
                            + "Amount owed is 18.5\n"
                            + "You earned 3 frequent renter points";

            Assert.AreEqual(expected, charles.Statement());
        }

        [TestMethod]
        public void StatementForJess()
        {
            Customer jess = new Customer("Jess");
            jess.Add(bh4DayRental);
            jess.Add(we7DRental);
            jess.Add(bh2DRental);

            string expected = "Rental Record for Jess\n"
                            + "\tBraveHeart\t12\n"
                            + "\tWall-E\t7.5\n"
                            + "\tBraveHeart\t6\n"
                            + "Amount owed is 25.5\n"
                            + "You earned 5 frequent renter points";

            Assert.AreEqual(expected, jess.Statement());
        }

        [TestMethod]
        public void StatementForRebecca()
        {
            Customer rebecca = new Customer("Rebecca");
            rebecca.Add(we7DRental);
            rebecca.Add(we3DRental);

            string expected = "Rental Record for Rebecca\n"
                            + "\tWall-E\t7.5\n"
                            + "\tWall-E\t1.5\n"
                            + "Amount owed is 9\n"
                            + "You earned 2 frequent renter points";

            Assert.AreEqual(expected, rebecca.Statement());
        }

        [TestMethod]
        public void StatementForLucas()
        {
            Customer lucas = new Customer("Lucas");
            lucas.Add(bh2DRental);
            lucas.Add(we7DRental);
            lucas.Add(we3DRental);

            string expected = "Rental Record for Lucas\n"
                            + "\tBraveHeart\t6\n"
                            + "\tWall-E\t7.5\n"
                            + "\tWall-E\t1.5\n"
                            + "Amount owed is 15\n"
                            + "You earned 4 frequent renter points";

            Assert.AreEqual(expected, lucas.Statement());
        }
    }
}

　　小结：这一篇并没有涉及具体的重构内容，而是一些重构前的准备：

　　　1.使用原始代码构造参考数据

　　　2.使用C#的单元测试框架为这些参考数据创建自动单元测试

　　至于这么做的最重要的原因是：为后面的重构提供可自动完成的、可重复执行的检验标准

　　相关代码打包下载：

　　http://download.youkuaiyun.com/detail/virtualxmars/4423635