Update:  'Seems I'm not the only one who's excited about the TDD potential that ASP.NET MVC opens up.  Phil Haack is already all over this one with his post Writing Testable Code Is About Managing Complexity.

I’m trying to curb my enthusiasm here, but I’m excited after reading this first part of ScottGu’s in-depth coverage on his team’s upcoming ASP.NET MVC Framework that we can expect to see in VS2008.

What’s got me really keyed-up is the potential that the MVC model will give us for unit testing web applications.  I could care two figs about the latest syntactic sugar that the product teams think we all want – they’re useless if I can’t do TDD (test-driven-development) and CI (continuous integration) against them.  And ASP.NET web apps have been public enemy #1 for most attempts to unit test – witness: SharePoint.

Here’s how Scott sees TDD happening under MVC (emphasis mine):

…part of what makes an MVC approach attractive is that we can unit test the Controller and Model logic of applications completely independently of the View/Html generation logic.  As you'll see below we can even unit test these before we create our Views.

The ASP.NET MVC framework has been designed specifically to enable easy unit testing.  All core APIs and contracts within the framework are interfaces, and extensibility points are provided to enable easy injection and customization of objects (including the ability to use IOC containers like Windsor, StructureMap, Spring.NET, and ObjectBuilder).  Developers will be able to use built-in mock classes, or use any .NET type-mocking framework to simulate their own test versions of MVC related objects.

The striking thing I see out of all of this is that Scott is envisioning an entirely new way of advancing the development paradigm:

1. ASP.NET MVC incorporates a best practice design pattern that’s long been known outside of our camp and one we’ve really wanted;
2. It’s taking some positive cues from our Ruby on Rails bretheren (eg. Models, Views and Controllers folders, ease of testing);
3. It is an alternative to, not a replacement for standard ASP.NET webforms – you can quite happily live in a coding cave if you wish;
4. You may use integrated MSFT technologies for testing and dependency injection, or use what you like, eg. NUnit, xUnit, Windsor, etc.

I like this.  I like this a lot.  I’m also hoping to hell that the higher-ups don’t foul this up for the rest of us – ScottGu’s on the right wavelength here and I’m really impressed he’s advancing so far with this.