How to await an async private method invoked using reflection in WinRT?

Question

I'm writing unit tests for a WinRT app, and I am able to invoke non-async private methods using this:

TheObjectClass theObject = new TheObjectClass(); Type objType = typeof(TheObjectClass); objType.GetTypeInfo()        .GetDeclaredMethod("ThePrivateMethod")        .Invoke(theObject, null); 

However, if the private method in question is async, the code will continue execution without waiting for it to finish.

How do I add await functionality to this?

Answer 1

Well you need to use the value returned by the method. Do you know the type? For example, if it's always a Task, you could use:

await (Task) objType.GetTypeInfo()                     .GetDeclaredMethod("ThePrivateMethod")                     .Invoke(theObject, null); 

If you don't know the return type but know it will be awaitable, you could use dynamic typing:

await (dynamic) objType.GetTypeInfo()                        .GetDeclaredMethod("ThePrivateMethod")                        .Invoke(theObject, null); 

I would try to avoid having to call a private method by reflection in your unit tests in the first place though. Can you test it indirectly via the public (or internal) API? That's generally preferable.

Answer 2

Invoke should return an object convertible to Task. Just await that.

If your private method returns void, then you'll need a custom SynchronizationContext, which is messy. It's better to have your methods return Task/Task<T>.