Mock in JUnit
<<Junit In Action>>是一本比较著名的关于JUnit的书。
当谈到JUnit单元测试技术的时候，举出了两种测试方法，Stub和Mock。Stub的大概概念如下：Stub是代码的一部分。其目的就是用简单的行为替换复杂的行为，从而允许独立地测试代码的一部分；Mock Object是使用来代替与你的代码协作的对象的对象，这样代码可以调用Mock Object的方法，这些方法的调用的结果是由你的测试设置好的。Stub适合替代代码中粗粒度的测试，通常用来替代成熟的外部系统，Mock技术能够提供更精细的控制，能够更完备地测试对象的行为。
下面是示例代码是关于Mock的一个例子。
测试目标代码：
public
class
Account
...
{
@SuppressWarnings("unused")privateStringaccountId;privatelongbalance;
publicAccount(StringaccountId,longinitialBalance)...{this.accountId=accountId;this.balance=initialBalance;
}publicvoiddebit(longamount)...{this.balance-=amount;}publicvoidcredit(longamount)...{this.balance+=amount;}publiclonggetBalance()...{returnthis.balance;}
}
public
interface
AccountManager
...
{publicAccountfindAccountForUser(StringuserId);publicvoidupdateAccount(Accountaccount);}
public
class
AccountService
...
{privateAccountManageraccountManager;publicvoidsetAccountManager(AccountManagermanager)...{this.accountManager=manager;}publicvoidtransfer(StringsenderId,StringbeneficiaryId,longamount)...{Accountsender=this.accountManager.findAccountForUser(senderId);Accountbeneficiary=this.accountManager.findAccountForUser(beneficiaryId);sender.debit(amount);beneficiary.credit(amount);this.accountManager.updateAccount(sender);this.accountManager.updateAccount(beneficiary);}}
测试代码：
public
class
MockAccountManager
implements
AccountManager
...
{privateHashtableaccounts=newHashtable();@SuppressWarnings("unchecked")publicvoidaddAccount(StringuserId,Accountaccount)...{this.accounts.put(userId,account);}publicAccountfindAccountForUser(StringuserId)...{return(Account)this.accounts.get(userId);}publicvoidupdateAccount(Accountaccount)...{//donothing}}
public
class
AccountServiceTest
extends
TestCase
...
{publicvoidtestTransfer()...{MockAccountManagermockAccountManager=newMockAccountManager();AccountsenderAccount=newAccount("1",200);AccountbeneficiaryAccount=newAccount("2",100);mockAccountManager.addAccount("1",senderAccount);mockAccountManager.addAccount("2",beneficiaryAccount);AccountServiceaccountService=newAccountService();accountService.setAccountManager(mockAccountManager);accountService.transfer("1","2",50);assertEquals(150,senderAccount.getBalance());assertEquals(150,beneficiaryAccount.getBalance());}}