使用事务自动回滚来实现单元测试

我们没有使用TDD，所以单元测试最麻烦的就是准备测试的基础数据。我们现在是使用内存仓储来做单元测试，要为每个仓储都构造基础数据，非常麻烦。

前几天看xunit的源码，看到AutoRollbackAttribute这个特性，异常的兴奋 ^_^。怎么就忘了用事务的自动回滚呢？

我们看AutorollbackAttribute的具体实现：

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public class AutoRollbackAttribute : BeforeAfterTestAttribute {     IsolationLevel isolationLevel = IsolationLevel.Unspecified;     TransactionScope scope;     TransactionScopeOption scopeOption = TransactionScopeOption.Required;     long timeoutInMS = -1;       /// <summary>     /// Gets or sets the isolation level of the transaction.     /// Default value is <see cref="IsolationLevel"/>.Unspecified.     /// </summary>     public IsolationLevel IsolationLevel     {         get { return isolationLevel; }         set { isolationLevel = value; }     }       /// <summary>     /// Gets or sets the scope option for the transaction.     /// Default value is <see cref="TransactionScopeOption"/>.Required.     /// </summary>     public TransactionScopeOption ScopeOption     {         get { return scopeOption; }         set { scopeOption = value; }     }       /// <summary>     /// Gets or sets the timeout of the transaction, in milliseconds.     /// By default, the transaction will not timeout.     /// </summary>     public long TimeoutInMS     {         get { return timeoutInMS; }         set { timeoutInMS = value; }     }       /// <summary>     /// Rolls back the transaction.     /// </summary>     public override void After(MethodInfo methodUnderTest)     {         scope.Dispose();     }       /// <summary>     /// Creates the transaction.     /// </summary>     public override void Before(MethodInfo methodUnderTest)     {         TransactionOptions options = new TransactionOptions();         options.IsolationLevel = isolationLevel;         if (timeoutInMS > 0)             options.Timeout = new TimeSpan(timeoutInMS * 10);         scope = new TransactionScope(scopeOption, options);     } }

这里使用了.Net Framework自带的TransactionScope。TransactionScope在.NET 2.0中就已经有了，可用于分布式事务。用这种方法来做数据的自动回滚也有一些不足：

1. 数据库要支持事务。
2. 内部数据库操作的逻辑里没有事务的实现。

很庆幸的是我们的项目正好都满足上面的2点，唯一不足的就是mongodb不支持事务。所以就需要混合仓储实现了，事务数据库使用真实的仓储，mongodb使用内存仓储。

项目中是用VS自带的单元测试框架，也不想因为这一个特性而改用xunit，那就只能动手把这个迁移到VS的单元测试框架里了。

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/// <summary> /// 单元测试基类 /// </summary> [TestClass] public class BaseUnitTest {     IsolationLevel _isolationLevel = IsolationLevel.Unspecified;     TransactionScopeOption _scopeOption = TransactionScopeOption.Required;     TransactionScope _transactionScope;     bool _openAutoRollback = true;       /// <summary>     /// 构造函数     /// </summary>     /// <param name="autoRollback">是否开启自动回滚，默认开启</param>     public BaseUnitTest(bool autoRollback = true)     {         _openAutoRollback = autoRollback;     }       /// <summary>     /// 自动回滚事务初始化     /// </summary>     [TestInitialize]     public void AutoRollbackBefore()     {         if (_openAutoRollback)         {             var options = new TransactionOptions();             options.IsolationLevel = _isolationLevel;             options.Timeout = new TimeSpan(0, 1, 0);             _transactionScope = new TransactionScope(_scopeOption, options);         }     }       /// <summary>     /// 自动回滚事务回滚并释放对象     /// </summary>     [TestCleanup]     public void AutoRollbackAfter()     {         if (_openAutoRollback)         {             if (_transactionScope == null)                 throw new InvalidOperationException("未初始化TransactionScope");             //回滚事务             _transactionScope.Dispose();             //释放事务对象             _transactionScope = null;             //移除所有的缓存             RemoveHttpRuntimeCache();         }     }       /// <summary>     /// 移除所有的HttpRuntime缓存     /// </summary>     [DebuggerStepThrough]     private void RemoveHttpRuntimeCache()     {         var cache = HttpRuntime.Cache.GetEnumerator();         var keys = new List<string>();         while (cache.MoveNext())         {             keys.Add(cache.Key.ToString());         }         foreach (var key in keys)         {             HttpRuntime.Cache.Remove(key);         }     }       /// <summary>     /// 设置不自动回滚事务     /// </summary>     protected void SetAutoRollbackIsUnavailabled()     {         _openAutoRollback = false;     } }

上面的RemoveHttpRuntimeCache是因为我们在项目中有使用HttpRuntime缓存，关系数据库中的数据回滚后会导致缓存和数据库不一致，所以一但有开启事务的自动回滚，也要相应的清空内存缓存。

方法很简单，跟大家分享一下，和TransactionScope相关的知识，不清楚的同学可以看下MSDN关于“TransactionScope”的文档。

原文地址：http://blog.moozi.net/archives/use-the-transaction-rollback-to-unit-test.html