If you’ve read my recent diatribes, you will be relived to know that this will be a very short post! It wasn’t going to be, but thankfully all the problems I was going to describe have been solved very simply.

Whilst tinkering around with my first Lightswitch application, I wanted to move some code into a separate class library, so it could be reused around the application. Naively, I added a C'# class library to the solution, moved the code over and then couldn’t add a reference to it from my Lightswitch project.

Whilst wondering what was going on, it dawned on me that Lightswitch is really just Silverlight underneath, so needs a Silverlight class library, not a normal .NET class library. I deleted the one I had just created, and added a new Silverlight C# class library. This time, I was able to add a reference and use the code from my Lightswitch application. Phew, one problem solved.

I then decided to write some unit tests for the class. That’s where I ran into the next problem. Normally, I just right-click a method, and choose “Create unit tests” from the context menu. Trouble was, there wasn’t a “Create unit tests” option there.

I spent rather longer than I should trying to work out how to do this, and failed. I even tried adding my own project and making into a test project, but that failed as I couldn’t add references to the appropriate test libraries. This is one of those occasions when you really wonder why Microsoft split Silverlight off from the rest of the .NET framework.

Anyway, the good news is that I just discovered that if you install the Silverlight Toolkit April 2010, you get new Visual Studio templates for unit testing Silverlight applications. They don’t work in quite the same way as normal unit tests, in that the tests themselves run in a Silverlight web application, but the basic principles are the same. You can even use the same code, and the same test attributes as you do in your normal tests.

Apparently, you can even test the UI with this framework, but I haven’t tried that. Needless to say, the fact that I could test my class library was enough to make me happy, and keep this blog post a lot shorter than it would have been - although it’s still a lot longer than it should have been, given the actual amount of useful information it contained! I must learn to be more concise.