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; /// /// Gets or sets the isolation level of the transaction. /// Default value is .Unspecified. /// public IsolationLevel IsolationLevel { get { return isolationLevel; } set { isolationLevel = value; } } /// /// Gets or sets the scope option for the transaction. /// Default value is .Required. /// public TransactionScopeOption ScopeOption { get { return scopeOption; } set { scopeOption = value; } } /// /// Gets or sets the timeout of the transaction, in milliseconds. /// By default, the transaction will not timeout. /// public long TimeoutInMS { get { return timeoutInMS; } set { timeoutInMS = value; } } /// /// Rolls back the transaction. /// public override void After(MethodInfo methodUnderTest) { scope.Dispose(); } /// /// Creates the transaction. /// 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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/// /// 单元测试基类 /// [TestClass] public class BaseUnitTest { IsolationLevel _isolationLevel = IsolationLevel.Unspecified; TransactionScopeOption _scopeOption = TransactionScopeOption.Required; TransactionScope _transactionScope; bool _openAutoRollback = true; /// /// 构造函数 /// /// 是否开启自动回滚，默认开启 public BaseUnitTest(bool autoRollback = true) { _openAutoRollback = autoRollback; } /// /// 自动回滚事务初始化 /// [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); } } /// /// 自动回滚事务回滚并释放对象 /// [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(); } } /// /// 移除所有的HttpRuntime缓存 /// [DebuggerStepThrough] private void RemoveHttpRuntimeCache() { var cache = HttpRuntime.Cache.GetEnumerator(); var keys = new List(); while (cache.MoveNext()) { keys.Add(cache.Key.ToString()); } foreach (var key in keys) { HttpRuntime.Cache.Remove(key); } } /// /// 设置不自动回滚事务 /// 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。