I have just released a new version of TestDriven.NET (2.7 Beta) with support for Silverlight/CoreCLR. Simply right click on the method you would like to execute with the CoreCLR and select 'Test With... Silverlight'. You can use this to execute any public methods (ad-hoc tests). I recommend you use 'Console.WriteLine' for any output messages. 'Trace.WriteLine' is supported by Silverlight's version of 'System.dll' but you would need to use something like DebugView to see the output.
Here is an example method being executed with Silverlight:
As shown above you do have access to the 'System.Windows.Browser.HtmlPage' static methods and properties (from the 'System.Silverlight' assembly). Hopefully people will find this feature useful for spelunking the Silverlight functionality.
I am working on proper unit testing support for Silverlight projects. At the moment none of the unit testing frameworks supported by TestDriven.NET (NUnit, MbUnit, MSTest or Zanebug) are compatible with the CoreCLR. I have had some success getting unit tests running using NUnitLite. You are welcome to contact me if you would like to try an early version of this.