模拟单元测试失败的OperationCanceledException场景

Question

我使用Moq4.18.2框架进行测试。

RtspClient可能会从ConnectAsync中抛出一个OperationCanceledException。所以，我试着测试这个场景。下面的测试抛出一个异常System.OperationCanceledException: The operation was canceled.，catch (OperationCanceledException)永远不会被执行。我在这里做错什么了？

RTSP

public interface IRtspClient : IDisposable
{
    event EventHandler<RawFrame> FrameReceived;

    Task ConnectAsync(CancellationToken token);
    Task ReceiveAsync(CancellationToken token);
}

使用的IRtspClient方法

public async Task ConnectAsync(CancellationToken token = default)
{
    try
    {
        await _rtspClient.ConnectAsync(token).ConfigureAwait(false);
        OnConnected();
    }
    catch (OperationCanceledException ex)
    {
        OnConnectAttemptCanceled(ex);
        throw;
    }
    catch(Exception ex)
    {
        OnFailedToConnect(ex);
        throw;
    }
}

测试

[TestMethod]
public async Task ConnectAsync_Canceled()
{
    var expectedCanceledTaskStatus = true;

    var tcs = new CancellationTokenSource();
    tcs.Cancel();
    var rtspClient = new Mock<IRtspClient>();
    rtspClient
        .Setup(_ => _.ConnectAsync(It.IsAny<CancellationToken>()))
        .Returns(Task.FromException<OperationCanceledException>(new OperationCanceledException()))

    var actualCanceledTaskStatus = false;
    var camera = new MyCamera(rtspClient.Object);
    camera.FailedToConnect += () => actualCanceledTaskStatus = true;
    await camera.ConnectAsync(tcs.Token);

    Assert.AreEqual(expectedCanceledTaskStatus, actualCanceledTaskStatus);
}

UPDATE按照@Dai的建议添加了缺失的await，但我的测试仍然失败。有人能看看测试代码吗？

Answer 1

我发现了我的错误(除了@Dai注意到的以外)。我应该将测试中的await camera.ConnectAsync放在try-catch中，或者使用Assert.ThrowsExceptionAsync。我选择了后者。以下是工作测试：

[TestMethod]
public async Task ConnectAsync_Canceled()
{
    var expectedTaskCanceledStatus = true;

    var rtspClient = new Mock<IRtspClient>();
    rtspClient
        .Setup(_ => _.ConnectAsync(default(CancellationToken)))
        .Returns(Task.FromException(new OperationCanceledException()));

    var actualTaskCanceledStatus = false;
    var camera = new MyCamera(rtspClient.Object);
    camera.ConnectAttemptCanceled += () => actualTaskCanceledStatus = true;

    await Assert.ThrowsExceptionAsync<OperationCanceledException>(async () => await camera.ConnectAsync());
    Assert.AreEqual(expectedTaskCanceledStatus, actualTaskCanceledStatus);
}

Answer 2

您需要将返回的block.

• Exceptions保存在try{}块内的
• --否则同步控制将立即将抛入匿名函数(或本地函数或lambda方法，或you delegate() try{})中的try{} Task保留在CancellationTokenSource is IDisposable中，因此您应该更改ConnectAsync_Canceled测试，将其封装在using()块中。H 216H 117也是如此，不要吞下异常--所以下面的代码捕获了两个异常，以便进行可能的调查，然后用throw; (don't use throw ex;: it resets the recorded stack-trace)重新抛出它们；相反，只需自己做throw; )。特别是带有request.

和/或TaskCanceledException的

• ，需要将异常重新抛回原始调用方(即CancellationTokenSource的所有者)；而如果在没有相应的Task“查看”的情况下捕获和处理TaskCanceledException，则调用方将假定操作成功，尽管取消了TaskCanceledException。

将代码更改为：

public async Task ConnectAsync( CancellationToken cancellationToken = default )
{
    try
    {
         await this.rtspClient.ConnectAsync(cancellationToken ).ConfigureAwait(false);

         this.OnConnected();
    }
    catch( OperationCanceledException cEx )
    {
        this.OnConnectAttemptCanceled( cEx );

        throw; // Re-throw so the `Task` representing *this method* (`ConnectAsync`) will report as Cancelled rather than Succeeded.
    }
    catch( Exception ex ) 
    {
        this.OnFailedToConnect( ex );

        throw; // Re-throw so the `Task` representing *this method* (`ConnectAsync`) will report as Failed rather than Succeeded.
    }
}