NUnit 异步测试导致 AppDomainUnloadedException

我有一个带有异步操作的 .NET 4.5 WCF 服务。我进行了集成测试，它使用 NetNamedPipeBinding 构建服务主机并通过客户端进行操作。

然而，每次这样的测试总是会导致 NUnit 报告以下内容：

System.AppDomainUnloadedException: Attempted to access an unloaded AppDomain. 
This can happen if the test(s) started a thread but did not stop it. 
Make sure that all the threads started by the test(s) are stopped before completion.

在我看来一切都很好。谁能看出可能是什么原因造成的？我在 GitHub 上有完整的代码示例：https://github.com/devlife/codesamples https://github.com/devlife/codesamples

我也有同样的问题。看起来问题似乎出在 WCF 用来处理异步 IO 的“宽松”完成端口线程（在线程池中）。

When ServiceHost.Close()使用时，它将向所有那些线程发出工作已完成的信号，但它们不会立即消失，也就是说，它们可能比线程结束还存活。ServiceHost.Close()手术。因此，由于测试运行结束，“关闭”过程与 NUnit 引起的实际 AppDomain 卸载发生竞争。

基本上，一个简单的Thread.Sleep(<a couple of seconds>)之后ServiceHost.Close()“修复”这个:-)

在互联网上进行了大量搜索之后，我找不到针对此问题的可靠解决方案（对于一系列类似的问题，但并非全部都是由于相同的原因，谷歌“单元测试appdomainunloadedexception”），缺乏某种方法来抑制这个警告本身。

我尝试了不同的绑定和传输（包括空传输 http://www.codeproject.com/Articles/20709/NullTransport-for-WCF），但没有效果。

最后我选择了这个“解决方案”：

static void PreventPrematureAppDomainUnloadHack()
{
    //
    // When NUnit unloads the test AppDomain, the WCF started IO completion port threads might
    // not have exited yet.
    // That leads to AppDomainUnloadedExceptions being raised after all is said and done.
    // While native NUnit, ReSharper oder TestDriven.NET runners don't show these, VSTest (and
    // TFS-Build) does. Resulting in very annoying noise in the form of build/test warnings.
    //
    // The following code _attempts_ to wait for all completion port threads to end. This is not
    // an exact thing one can do, however we mitigate the risk of going wrong by several factors:
    // (1) This code is only used during Unit-Tests and not for production code.
    // (2) It is only called when the AppDomain in question is about to go away anway.
    //     So the risk of someone starting new IO threads while we're waiting is very
    //     low.
    // (3) Finally, we have a timeout in place so that we don't wait forever if something
    //     goes wrong.
    //
    if (AppDomain.CurrentDomain.FriendlyName.StartsWith("test-domain-", StringComparison.Ordinal))
    {
        Console.WriteLine("AppDomainUnloadHack: enabled (use DbgView.exe for details).");
        Trace.WriteLine(string.Format("AppDomainUnloadHack: enabled for domain '{0}'.", AppDomain.CurrentDomain.FriendlyName));

        AppDomain.CurrentDomain.DomainUnload += (sender, args) =>
        {
            int activeIo;
            var sw = Stopwatch.StartNew();
            var timeout = TimeSpan.FromSeconds(3);

            do
            {
                if (sw.Elapsed > timeout)
                {
                    Trace.WriteLine("AppDomainUnloadHack: timeout waiting for threads to complete.");
                    sw.Stop();
                    break;
                }

                Thread.Sleep(5);

                int maxWorkers;
                int availWorkers;
                int maxIo;
                int availIo;
                ThreadPool.GetMaxThreads(out maxWorkers, out maxIo);
                ThreadPool.GetAvailableThreads(out availWorkers, out availIo);
                activeIo = maxIo - availIo;

                Trace.WriteLine(string.Format("AppDomainUnloadHack: active completion port threads: {0}", activeIo));

            } while (activeIo > 0);

            Trace.WriteLine(string.Format("AppDomainUnloadHack: complete after {0}", sw.Elapsed));
        };
    }
}

3 秒的超时是完全任意的，每次重试之间的 5 毫秒的等待也是任意的。有时我确实会遇到“超时”，但大多数时候它都有效。

我确保每个测试程序集都调用此代码一次（即通过引用类型的静态构造函数）。

像往常一样，在这种情况下YMMV。