Question

I’m receiving event notifications from web services that trigger event handlers with data regarding what triggered the event. I’m trying to test that once an event handler is called that a, b and c are all called with the proper values. This isn’t possible without relying on the web service

My solution is to create converters that convert the EventArgs that are returned to my via the services library (Exchange Web Services) to something my dumb objects can understand without relying on third part services. My issue is that the EventArgs class given to my by the EWS library has an internal constructor so there’s no easy way to generate an instance of it with random property values without much work with reflection.

For example, I have a simply interface:

public interface IConverter<TFrom, TTo>
{
    TTo Convert(TFrom from);
}

and a simple implementation:

public class NotificationEventArgsConverter : IConverter<NotificationEventArgs, NewNotification>
{
    public NewNotification Convert(NotificationEventArgs from)
    {
        return new NewNotification
                   {
                       ItemIds = from.Events.Cast<ItemEvent>().Select(x => x.ItemId.ToString())
                   };
    }
}

Question is how can I generate an instance of NotificationEventArgs with random values. Is there a library for this that I missed in my searches?

The entire goal of this is to emulate if I receive an instance of NotificationEventArgs with the following values then NewNotification should resemble x.

Edit

In the meantime I will simply use typeof(T).GetConstructor().

Answer 1

You might want to take a look at AutoFixture:

AutoFixture makes it easier for developers to do Test-Driven Development by automating non-relevant Test Fixture Setup, allowing the Test Developer to focus on the essentials of each test case.

After doing some decompilation of Microsoft.Exchange.WebServices and playing bit with reflection, you can do it for example like this:

var fixture = new Fixture();

// retrieve internal FolderEvent(EventType, DateTime) ctor
// using FolderEvent class as NotificationEvent is abstract
var notificationEventCtor = typeof(FolderEvent).GetConstructor(
    BindingFlags.NonPublic | BindingFlags.Instance,
    null,
    new Type[] { typeof(EventType), typeof(DateTime) },
    null
);

// generate 10 random events with some help of LINQ and AutoFixture
var trashData = Enumerable
    .Range(1, 10)
    .Select(i => new object[]
        {
            fixture.CreateAnonymous<EventType>(),
            fixture.CreateAnonymous<DateTime>() 
        })
    .Select(p => notificationEventCtor.Invoke(p))
    .Cast<NotificationEvent>()
    .ToList();

Code above will generate 10 FolderEvents in a list, ready to pass to NotificationEventArgs constructor (which is internal again, so same code applies):

var notificationEventArgsCtor = typeof(NotificationEventArgs).GetConstructor(
    BindingFlags.NonPublic | BindingFlags.Instance,
    null,
    new Type[] 
    { 
        typeof(StreamingSubscription),
        typeof(IEnumerable<NotificationEvent>) 
    },
    null
);

var instance = notificationEventArgsCtor
    .Invoke(new object[] { null, trashData });