Nunit async test exception assertion

Question

[Edit (May 2020)] - This issue has been reportedly addressed in newer releases of NUnit. Please see Nunit.ThrowsAsync. (Ref this answer, thanks @James-Ross)

Answer 1

If you await a Task then Exceptions that are thrown are aggregated into AggregateException. You can inspect the inner exceptions of AggregateException. This could be the reason why you case 2 does not work.

Unhandled exceptions that are thrown by user code that is running inside a task are propagated back to the joining thread, except in certain scenarios that are described later in this topic. Exceptions are propagated when you use one of the static or instance Task.Wait or Task.Wait methods, and you handle them by enclosing the call in a try-catch statement. If a task is the parent of attached child tasks, or if you are waiting on multiple tasks, then multiple exceptions could be thrown. To propagate all the exceptions back to the calling thread, the Task infrastructure wraps them in an AggregateException instance. The AggregateException has an InnerExceptions property that can be enumerated to examine all the original exceptions that were thrown, and handle (or not handle) each one individually. Even if only one exception is thrown, it is still wrapped in an AggregateException.

Link to MSDN