I have a method (some code removed):
try
{
var task = Task.Factory.StartNew(ValidateAccounts, _token);
}
catch (AggregateException)
{
_tokenSource = new CancellationTokenSource();
_token = _tokenSource.Token;
}
ValidateAccounts is a private method withing the same class. I would like to test that it was called and would like to be able to mock the task and try with the exception thrown and without it.
As others have mentioned, you have to be careful when treading the fine line of what-to-test vs. what-not-to-test. It can lead to brittle tests that are too coupled with the implementation.
That being said, I absolutely see the utility in doing what you're trying to do. Testing the exception handling alone is worth asking this question.
The problem is rooted in your use of a static object (Task.Factory). Static objects/methods are notorious for impeding testability. The solution to this problem is the same used for decoupling any type of static object - introducing a seam.
You are using the static object to kick off, and return a reference to, a Task. This is something that you can define a role interface for. It might look something like:
public interface ITaskFactory
{
Task StartNew(Action action);
}
With a production implementation that looks like:
public class TplTaskFactory : ITaskFactory
{
public Task StartNew(Action action)
{
return Task.Factory.StartNew(action);
}
}
You could then use dependency injection to supply your SUT with a mock implementation of this interface, which gives you the capability you're looking for.
