In my day job I and my teams write unit tests for all of our code and we write our projects to be testable, this gives great benefits and actaully makes your projects go faster. My current porject has a code coverage of 80%+ and we have nearly 800 tests written already. The really cool thing about having Unit tests for all of your code is that when you or someone else needs to cahnge some part of the solution you simply run the tests afterwards to make sure you didnt break anything elsewhere.
The other thing we do is when a bug is reported by the Test Team, who write our automation tests with Watin, we firstly write a test to prove there is a bug and then mod the code to fix the bug. This gives us an extra set of tests that test the edge case we missed before and thus makes the code even stronger.
And yet another benefit of unti testing is that you can include the tests in your load tests to measure performance.
So with all these great reasons to write unit tests I have started building a template DNN module that can be fully unit tested. I have created a new Forge project here http://www.codeplex.com/TestDrivenDNNModule . You can download the template and see how Im doing it. One of the things you will find is that to write unit tests for ASP.Net apps you need to be able to separate out the functional code from the normal code behind file to conduct a proper uint test. To do this I have used the Passive View Pattern from Martin Fowler. I was put onto this by Dan Bartholomew who discovered it is very similar to the pattern in the WCSF.
If you look in the code behind file you'll see that the only code is to set properties and to call the methods in the Presenter class which ahs all the functioanl code. The code in teh code behind does not need to be unit tested as it only sets and gets properties or triggers an event. The code in the presenter class is what gets tested.
My next task is to add in the mocking of each layer using RhinoMocks so that i can unit test each part of the Presenter code without worrying about hitting code further down the stack such as the Controller class and data providers. Dan is helping me out on that so we should have some more of the template done next week.