Pex在探索时会引发NullReferenceException

我正在用C#编写一个服务器组件，并使用Pex进行单元测试。

我有一个针对特定方法的复杂参数化单元测试。现在事实证明，一旦我添加了某个断言块，一些 pex 探索运行就会失败，在我的方法的结束行（就在括号处）出现 NullReferenceException。当我调试失败的运行时，它运行绝对正常。

我犯了一个错误还是这是 pex 中的错误？

谢谢！

[PexMethod]
public Task Start(CancellationToken cancellationToken,
    int workingEndpoints, // endpoints that run succesfully
    int failingEndpoints, // endpoints that fail immidiatly
    int brokenEndpoints) // endpoints that return null for their task
{
    PexAssume.IsTrue(workingEndpoints >= 0);
    PexAssume.IsTrue(failingEndpoints >= 0);
    PexAssume.IsTrue(brokenEndpoints >= 0);
    PexAssume.IsTrue(workingEndpoints + failingEndpoints + brokenEndpoints >= 1);
    // create fake endpoints based on the count
    List<IHostEndpoint> fakeEndpoints = new List<IHostEndpoint>();
    Exception failedTaskException = new Exception();
    // Create a few endpoint stubs for testing purposes and add them to the  list (commented away for relevance)
    // create and start the host
    Host host = new Host(fakeEndpoints.ToArray());
    Task result = host.Start(cancellationToken);
    PexAssert.IsNotNull(result);
    if (failingEndpoints > 0 || brokenEndpoints > 0)
    {
        PexAssert.IsNotNull(result.Exception);
        int failedEndpointExceptionCount = 0;
        int brokenEndpointExceptionCount = 0;
        result.Exception.Flatten().Handle(innerException =>
        {
            if (innerException == failedTaskException)
                failedEndpointExceptionCount++;
            else
                brokenEndpointExceptionCount++;
            return true;
        });
        // after one broken endpoint, the run method should stop starting more endpoints
        int brokenEndpointExpectedCount = Math.Min(1, brokenEndpoints);
        PexAssert.AreEqual(failedEndpointExceptionCount, failingEndpoints);
        PexAssert.AreEqual(brokenEndpointExceptionCount, brokenEndpointExpectedCount); 
    }
    return result;            
}

编辑

一个假设可能是由于异步代码，Pex遇到了一些问题。我已经检查了每一次运行，甚至伪造了主机的启动方法。没有异步方法。在某些情况下，我确实创建了 1 个任务，但我同步运行它（下面的证明）

Task endpointTask = endpoint.Start(innerCancellationToken);                
if (endpointTask == null)
{
    // This endpoint is broken, for simplicity we raise an exception in the normal pipe
    Task faultedTask = new Task(() =>
    {
        throw new InvalidOperationException("Endpoint returned a null valued task which is not allowed");
    });
    faultedTask.RunSynchronously();
    innerTasks.Add(faultedTask);
    break;
}
else
{
    innerTasks.Add(endpointTask);
}

IHostEndpoint 存根是使用 TaskCompletionSource 创建的，并直接设置了值/状态。