I posted a batch file
here that I use.
I make this part of my project folder in Eclipse so in the package explorer I can directly just double click on it. This rebuilds the zip, re-installs it into Calibre and starts calibre in debug mode. You just need to remember to close Calibre before you next run it again.
You can directly test preferences configuration screens etc using __main__ test stubs in the class files but I've never really found that particularly useful for user interface plugins, mainly because I am wanting to test the result of changing a setting rather than just the configuration screen itself.