让代码可测试化
本篇介绍如何把我们目前最常见的代码转换为可以单元测试的代码，针对业务逻辑层来实现可测试性，我们以银行转账为例，通常代码如下：
|
public class TransferController { private TransferDAL dal = new TransferDAL(); public bool TransferMoney(string fromAccount, string toAccount, decimal money) { //验证：比如账号是否存在、账号中是否有足够的钱用来转账 if (fromAccount == null || fromAccount.Trim().Length == 0) return false; if (toAccount == null || toAccount.Trim().Length == 0) return false; if (IsExistAccount(fromAccount))//检查from账号是否存在 return false; if (IsAccountHasEnoughMoney(fromAccount))//检查from账号中是否有足够的钱用来转账 return false; //更新数据库 dal.TransferMoney(fromAccount, toAccount, money); //发送邮件 EmailSender.SendEmail("aaa@aa.com", "xxxxxxxx", "yyyyyyyyyy"); return true; } private bool IsAccountHasEnoughMoney(string fromAccount) { throw new System.NotImplementedException(); } private bool IsExistAccount(string fromAccount) { throw new System.NotImplementedException(); } } |
|
相应sql语句如下： public void TransferMoney(string fromAccount, string toAccount, decimal money) { string sql = @" UPDATE Accounts SET Money=Money-@Money WHERE Account=@FromAccount UPDATE Accounts SET Money=Money+@Money WHERE Account=@FromAccount "; } |
扎眼一看，这转账操作的逻辑写在了sql语句中（没有弱化外部操作），这样就会导致对业务逻辑代码的不可测试性，因此需要重构转账的计算部分，改成如下：
|
public class TransferController { private TransferDAL dal = new TransferDAL(); public bool TransferMoney(string fromAccount, string toAccount, decimal money) { //验证：比如账号是否存在、账号中是否有足够的钱用来转账 if (fromAccount == null || fromAccount.Trim().Length == 0) return false; if (toAccount == null || toAccount.Trim().Length == 0) return false; if (IsExistAccount(fromAccount))//检查from账号是否存在 return false; if (IsAccountHasEnoughMoney(fromAccount))//检查from账号中是否有足够的钱用来转账 return false; //更新数据库 using(TransactionScope ts=new TransactionScope()) { dal.MinuseMoney(fromAccount, money); dal.PlusMoney(toAccount, money); ts.Complete(); } //发送邮件 EmailSender.SendEmail("aaa@aa.com", "xxxxxxxx", "yyyyyyyyyy"); return true; } private bool IsAccountHasEnoughMoney(string fromAccount) { throw new System.NotImplementedException(); } private bool IsExistAccount(string fromAccount) { throw new System.NotImplementedException(); } } |
相对于业务逻辑层来说，分析出外部接口有：邮件发送、数据访问对象，因此增加这2个接口到代码中，变成如下：
|
public class TransferController { private ITransferDAO dao = new TransferDAL(); private IEmailSender emailSender=new XXXXXXXXXXXXXXX();//由于一般的email发送类都是static的，不能new，这部分先留着，等下一步解决 public bool TransferMoney(string fromAccount, string toAccount, decimal money) { //验证：比如账号是否存在、账号中是否有足够的钱用来转账 if (fromAccount == null || fromAccount.Trim().Length == 0) return false; if (toAccount == null || toAccount.Trim().Length == 0) return false; if (IsExistAccount(fromAccount))//检查from账号是否存在 return false; if (IsAccountHasEnoughMoney(fromAccount))//检查from账号中是否有足够的钱用来转账 return false; //更新数据库 using(TransactionScope ts=new TransactionScope()) { this.dao.MinuseMoney(fromAccount, money); this.dao.PlusMoney(toAccount, money); ts.Complete(); } //发送邮件 this.emailSender.SendEmail("aaa@aa.com", "xxxxxxxx", "yyyyyyyyyy"); return true; } private bool IsAccountHasEnoughMoney(string fromAccount) { throw new System.NotImplementedException(); } private bool IsExistAccount(string fromAccount) { throw new System.NotImplementedException(); } } |
但是此时的2个接口，实际系统运行过程中还是会强耦合2个具体类，还是不可测试，怎么办呢？利用构造函数注入：
|
public class TransferController { private ITransferDAO dao; private IEmailSender emailSender; public TransferController()//实际运行时可以用这个构造 { dao = new TransferDAL(); emailSender = new EmailSenderAgent(); } public TransferController(ITransferDAO dao, IEmailSender emailSender)//测试时用这个构造注入Fake对象 { this.dao = dao; this.emailSender = emailSender; } public bool TransferMoney(string fromAccount, string toAccount, decimal money) { //验证：比如账号是否存在、账号中是否有足够的钱用来转账 if (fromAccount == null || fromAccount.Trim().Length == 0) return false; if (toAccount == null || toAccount.Trim().Length == 0) return false; if (IsExistAccount(fromAccount))//检查from账号是否存在 return false; if (IsAccountHasEnoughMoney(fromAccount))//检查from账号中是否有足够的钱用来转账 return false; //更新数据库 using(TransactionScope ts=new TransactionScope()) { this.dao.MinuseMoney(fromAccount, money); this.dao.PlusMoney(toAccount, money); ts.Complete(); } //发送邮件 this.emailSender.SendEmail("aaa@aa.com", "xxxxxxxx", "yyyyyyyyyy"); return true; } private bool IsAccountHasEnoughMoney(string fromAccount) { throw new System.NotImplementedException(); } private bool IsExistAccount(string fromAccount) { throw new System.NotImplementedException(); } } |
终于，可以编写单元测试了，看下面：
|
class TransferMoneyTest { public void TransferMoney_Validate_FromAccount_Null_Test() { string fromAccount=null; string toAccount="bbbbbbbbbbbb"; decimal money=100; TransferController ctl = new TransferController(null, null);//因为这个测试用不到这2个接口，所以用了null bool real= ctl.TransferMoney(fromAccount, toAccount, money); Assert.IsFalse(real); } public void TransferMoney_Validate_FromAccount_Empty_Test() { string fromAccount = ""; string toAccount = "bbbbbbbbbbbb"; decimal money = 100; TransferController ctl = new TransferController(null, null);//因为这个测试用不到这2个接口，所以用了null bool real = ctl.TransferMoney(fromAccount, toAccount, money); Assert.IsFalse(real); } public void TransferMoney_Validate_FromAccount_AllSpace_Test() { string fromAccount = " "; string toAccount = "bbbbbbbbbbbb"; decimal money = 100; TransferController ctl = new TransferController(null, null);//因为这个测试用不到这2个接口，所以用了null bool real = ctl.TransferMoney(fromAccount, toAccount, money); Assert.IsFalse(real); } public void TransferMoney_Validate_FromAccount_NotExist_Test() { string fromAccount = "11111111111111"; string toAccount = "bbbbbbbbbbbb"; decimal money = 100; ITransferDAO dao = new FakeTransferDAO_NullAccount(); TransferController ctl = new TransferController(dao, null);//因为这个测试用不到IEmailSender接口，所以用了null bool real = ctl.TransferMoney(fromAccount, toAccount, money); Assert.IsFalse(real); } public void TransferMoney_Validate_FromAccount_NotEnoughMoney_Test() { string fromAccount = "11111111111111"; string toAccount = "bbbbbbbbbbbb"; decimal money = 100; ITransferDAO dao = new FakeTransferDAO_NotEnoughMoney(); TransferController ctl = new TransferController(dao, null);//因为这个测试用不到IEmailSender接口，所以用了null bool real = ctl.TransferMoney(fromAccount, toAccount, money); Assert.IsFalse(real); } } |
|
用到了如下2个Fake类 class FakeTransferDAO_NullAccount : ITransferDAO { public void MinuseMoney(string fromAccount, decimal money) { throw new NotImplementedException(); } public void PlusMoney(string toAccount, decimal money) { throw new NotImplementedException(); } public Account GetAccount(string accountId) { return null; } } class FakeTransferDAO_NotEnoughMoney: ITransferDAO { public void MinuseMoney(string fromAccount, decimal money) { throw new NotImplementedException(); } public void PlusMoney(string toAccount, decimal money) { throw new NotImplementedException(); } public Account GetAccount(string accountId) { Account account = new Account(); account.Money = 20; return account; } } |
暂时先写到这里，呵呵...