NSubstitute – mock throwing an exception in method returning Task

Actually, the accepted answer mocks a synchronous exception being thrown, that is not the real async behavior. The correct way to mock is:

var myService = Substitute.For<IMyService>();
myService.GetAllAsync()
         .Returns(Task.FromException<List<object>>(new Exception("some error")));

Let’s say you had this code and GetAllAsync()

try
{
    var result = myService.GetAllAsync().Result;
    return result;
}
catch (AggregateException ex)
{
    // whatever, do something here
}

The catch would only be executed with Returns(Task.FromException>(), not with the accepted answer since it synchronously throws the exception.