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标题: NMock2入门经验 [打印本页]

作者: maguschen 时间: 2008-4-24 13:35
标题: NMock2入门经验
每个做单元测试的人都应该一种技术--MOCK~什么是MOCK？其实没什么神秘的，就是打桩~网上流行的一些.NET的mock框架有：NMock2，Rhino.Mocks等……
NMock2是ThoughtWorks维护的一个开源项目，不知道是不是ThoughtWorks的风格就是敏捷开发基本没有文档，网络上很难找到关于NMock2的文档。而且网上给的例子也很简单，简单到需要自己补充一些东西上去才能跑通。还是用官网上的那个例子：现在有一个银行系统，它实现了一个功能，就是允许两个同名帐户之间实现转账功能。但是很不巧的是，在两个帐户之间转账涉及到汇率的问题，而这个汇率又是天天变的，需要从一个外部的服务来实现的。简单来说就是：
一个接口：IAccountService，实现转账的功能
public interface IAccountService
{
      void TransferFunds(Account from, Account to, double amount);
}
一个接口：ICurrencyService，实现获取汇率的功能
public interface ICurrencyService
{
      double GetConversionRate(string fromCurrency, string toCurrency);
}
一个类：Account，就是一个一个的帐户
public class Account
{
      private double _balance;
      private string _name;
      private string _currency;
      public double balance
      {
         get
         {
            return _balance;
         }
         private set
         {
            _balance = value;
         }
      }
      public string name
      {
         get
         {
            return _name;
         }
         set
         {
            _name = value;
         }
      }
      public string Currency
      {
         get
         {
            return _currency;
         }
         set
         {
            _currency = value;
         }
      }
      public Account()
      {
         this.name = null;
         this.Currency = null;
      }
      public Account(string name, string currency)
      {
         this.name = name;
         this.Currency = currency;
      }
      public void Withdraw(double amount)
      {
         this.balance -= amount;
      }
      public void Deposit(double amount)
      {
         this.balance += amount;
      }
}
还有一个实现了IAccountService接口的AccountService类
public class AccountService : IAccountService
{
      private readonly ICurrencyService currencyService;
      public AccountService(ICurrencyService currencyService)
      {
         this.currencyService = currencyService;
      }
      public void TransferFunds(Account from, Account to, double amount)
      {
         from.Withdraw(amount);
         double conversionRate = currencyService.GetConversionRate(from.Currency, to.Currency);
         double convertedAmount = amount * conversionRate;
         to.Deposit(convertedAmount);
      }
}
这里我们就对ICurrencyService接口实现一个Mock，给测试程序传递一个假的对象
首先在NUnit的代码里面定义需要用到的对象
      Mockery mocks;
      ICurrencyService mockCurrencyService;
      IAccountService accountService;
然后在单元测试的TestInitialize方法里面初始化mock
      mocks = new Mockery();  //初始化mocks
      mockCurrencyService = mocks.NewMock<ICurrencyService>(); //产生一个mock对象
      accountService = new AccountService(mockCurrencyService); //用mock对象初始化accountService
最后就是测试的代码：
      public void ShouldUseCurrencyServiceToDetermineConversionRateBetweenAccounts()
      {
         //生成2个帐号
         Account canadianAccount = new Account("John Doe", "CAD");
         Account britishAccount = new Account("Jane Doe", "GBP");
         /给英国人存100块
         britishAccount.Deposit(100);

         Expect.Once.On(mockCurrencyService).
            Method("GetConversionRate").
            With("GBP", "CAD").
            Will(Return.Value(2.20));//对于mockCurrencyService对象，如果他的GetConversionRate方法被调用，而且参数分别是("GBP", "CAD")，那么就返回一个值2.20

         accountService.TransferFunds(britishAccount, canadianAccount, 100);
         Assert.AreEqual((double)0, britishAccount.balance,0.00001);
         Assert.AreEqual((double)220, canadianAccount.balance,0.00001);
         mocks.VerifyAllExpectationsHaveBeenMet();
      }

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