xUnit Async Test Not Working Properly

Question

We have been using xUnit Framework in our project as test framework since the begining. Currently there are 2200+ unit tests in project and everything seems fine.

Bu

Answer 1

The problem is that async void method does not return a Task object which xUnit could possibly examine for exceptions. xUnit cannot even track the completion of a particular async void method, as opposed to an async Task method.

Moreover, async void methods do not throw exceptions on the same stack frame, even for exceptions thrown from the synchronous part of the method. Rather, exceptions are propagated to the current synchronization context via SynchronizationContext.Post (in case SynchronizationContext.Current != null), or otherwise via ThreadPool.QueueUserWorkItem. This behavior is different from async Task methods, more details. It's possible to track the total number of the pending async void methods (via SynchronizationContext.OperationStarted/OperationCompleted), but not individual methods.

So, changing the XunitTestMethod_Async method's signature from async void to async Task should solve the problem.

Updated, it's 2019 and as @maracuja-juice points out, both asynv void tests now fail, as they original should have behaved. xUnit team has implemented AsyncTestSyncContext, their special flavor of synchronization context, an instance of which they install to individually track each async void call and capture any exceptions.