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
一个接口:ICurrencyService,实现获取汇率的功能

    public interface IAccountService

    {
         void TransferFunds(Account from, Account to, double amount);
    }

    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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