Question

我无法弄清楚为什么在我的单元测试调试期间没有断点时抛出异常。但是，当我使用在以下行设置的断点进行调试时，它运行正常。

这是我的代码。

MainPageViewModel.cs

public class MainPageViewModel
{
    public async Task<IEnumerable<Event>> GetAllEvents()
    {
        WebClient client = new WebClient();
        string xmlDoc = await FXNewsAlert.Misc.Extensions.DownloadStringTask(client, new Uri("http://www.forexfactory.com/ffcal_week_this.xml")); //breakpoint here

        var events = XDocument.Parse(xmlDoc)
            .Descendants("event")
            .Select(n => new Event
            {
                Title = n.Element("title").Value,
                Country = n.Element("country").Value,
                DateTime = this.ToLocalTime(String.Format("{0} {1}", n.Element("date").Value, n.Element("time").Value)),
                Impact = n.Element("forecast").Value,
                Forecast = n.Element("forecast").Value,
                Previous = n.Element("previous").Value
            }).ToList();

        return events;
    }
}

EventsTest.cs

[TestClass]
public class EventsTest : WorkItemTest
{
    [TestMethod]
    [Asynchronous]
    public async void GetAllEventsTest()
    {
        MainPageViewModel vm = new MainPageViewModel();
        IEnumerable<Event> events = await vm.GetAllEvents(); //WebException is thrown here.

        Assert.IsTrue(events.Count() > 0);
        EnqueueTestComplete();
    }
}

我的猜测是，以某种方式加载网址需要时间，因此通过设置断点，它会给予额外的时间，以便我可以按时完成下载的xml。

但它实际上是一种异步方法，所以没关系吧？我现在几乎迷路了。任何帮助将不胜感激。

编辑： DownloadStringTask的实现

    public static Task<string> DownloadStringTask(this WebClient webClient, Uri uri)
    {
        var tcs = new TaskCompletionSource<string>();

        webClient.DownloadStringCompleted += (s, e) =>
        {
            if (e.Error != null)
            {
                tcs.SetException(e.Error);
            }
            else
            {
                tcs.SetResult(e.Result);
            }
        };

        webClient.DownloadStringAsync(uri);

        return tcs.Task;
    }

System.Net.WebException的StackTrace

在System.Net.Browser.AsyncHelper.BeginOnUI（SendOrPostCallback beginMethod，Object state）在System.Net.Browser.ClientHttpWebRequest.EndGetResponse（IAsyncResult asyncResult）在System.Net.WebClient.GetWebResponse（WebRequest请求，IAsyncResult结果）在System.Net.WebClient.DownloadBitsResponseCallback（IAsyncResult结果） ---从抛出异常的先前位置开始的堆栈跟踪结束--- 在System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess（任务任务）在System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification（任务任务）在System.Runtime.CompilerServices.TaskAwaiter 1.GetResult() at FXNewsAlert.Resources.MainPageViewModel.<GetAllEvents>d__2.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Runtime.CompilerServices.TaskAwaiter 1.GetResult（）在FXNewsAlertTest.UnitTests.EventsTest.d__0.MoveNext（）

Answer 1

我觉得FXNewsAlert出了问题，上面没有介绍它的实现。我建议深入研究（或替换）FXNewsAlert.Misc.Extensions.DownloadStringTask()。我的猜测是它在完成下载之前就已经屈服了。

为了测试这段代码，我首先创建了一个Event类来包含数据，并尽量减少对代码的更改：

public class Event
{
    public string Title { get; set; }
    public string Country { get; set; }
    public DateTime DateTime { get; set; }
    public string Impact { get; set; }
    public string Forecast { get; set; }
    public string Previous { get; set; }
}

然后我稍微修改了你的代码以使用WebClient的DownloadStringTaskAsync()方法：

public class MainPageViewModel
{
    public async Task<IEnumerable<Event>> GetAllEvents()
    {
        WebClient client = new WebClient();

        // HACK: Don't have access to the implementation to FXNewsAlert...
        //string xmlDoc = await FXNewsAlert.Misc.Extensions.DownloadStringTask(
        //    client, new Uri("http://www.forexfactory.com/ffcal_week_this.xml")); //breakpoint here

        string xmlDoc = await client.DownloadStringTaskAsync(
            new Uri("http://www.forexfactory.com/ffcal_week_this.xml")); //breakpoint here

        var events = XDocument.Parse(xmlDoc)
            .Descendants("event")
            .Select(n => new Event
            {
                Title = n.Element("title").Value,
                Country = n.Element("country").Value,
                DateTime = DateTime.Parse(String.Format("{0} {1}", n.Element("date").Value, n.Element("time").Value)),
                Impact = n.Element("forecast").Value,
                Forecast = n.Element("forecast").Value,
                Previous = n.Element("previous").Value
            }).ToList();

        return events;
    }
}

我没有创建测试项目，而是掀起了以下控制台应用程序：

class Program
{
    static void Main(string[] args)
    {
        var vm = new MainPageViewModel();
        var task = vm.GetAllEvents();
        task.Wait();
        foreach (Event e in task.Result)
        {
            Console.WriteLine("{0} [{1}]", e.Title, e.DateTime);
            Console.WriteLine("Forecast: {0} (Previous: {1})", e.Forecast, e.Previous);
            Console.WriteLine();
        }
    }
}

此代码在有和没有断点的情况下都可以正常执行。

Answer 2

将您的测试方法从async void更改为async Task。

这不会清除WebException，但它应该保持一致，以便您可以调试它。

未设置断点时，在单元测试期间抛出异常

2 个答案: