unit testing asynchronous operation

Question

I want to unit test a method that I have that performs and async operation:

 Task.Factory.StartNew(() =>
        {
            // method to test and return v         


        

Answer 1

You'd have to have some way of faking out the task creation.

If you moved the Task.Factory.StartNew call to some dependency (ILongRunningOperationStarter) then you could create an alternative implementation which used TaskCompletionSource to create tasks which complete exactly where you want them to.

It can get a bit hairy, but it can be done. I blogged about this a while ago - unit testing a method which received tasks to start with, which of course made things easier. It's in the context of async/await in C# 5, but the same principles apply.

If you don't want to fake out the whole of the task creation, you could replace the task factory, and control the timing that way - but I suspect that would be even hairier, to be honest.