How to Debug or Test your Windows Service Without Installing it...

Along similar lines to KeithAMS, when writing a windows service I only use the Windows Service Project as a container to run code that is in one or more referenced assemblies. As far as I'm concerned, if I've got any logic that goes beyond starting and stopping the service in my service project then I've made an error in separating the concerns of the application.

Testing the referenced assemblies by themselves is easy enough with the multitude of unit testing frameworks and automated build tools that are available for free these days.