How to Unit Test a ViewModel with async method.

Question

I am not sure where to start but let me give you a brief idea on where I am and what I want to achieve. I am quite new to Unit Testing on MVVM and having difficulty on testing t

Answer 1

Your method GetTasksAsync should return a Task so you can actually wait for it.

I recommend this series on Channel9 an specially this episode explaining your problem.

Just to make is clear: Simply changing the signature of GetTasksAsync to

Task GetTasksAsync();

allows you to do this:

var t = GetAsync();
t.Wait();
Assert(...);

In case you really want to test the command in your unit tests and not the actually method called by the command you can use a field in your ViewModel to store the task to await (not so clean) or replace your DelegateCommand by something like described in this post: Awaitable DelegateCommand

Update: In addition to the blog post and considering you are using PRISM, you should have a look a Project Kona from the same team as PRISM. They actually implemented DelegateCommand to support AsyncHandlers