This all assumes that your Grails app has tests which exercise the code in these plugins. The proper way to package your tests of course is to have them sitting in each plugin. I am about to refactor and do this soon.
Feel free to resolve this issue immediately, or delete it if you find it bothersome. :)
This is actually not an issue at all but I thought worthwhile to document here in case others land on this page in a web search.
If you improperly designed you Grails app initially like me and want to get a coverage report for not only the Grails app you're working but also its plugins (and also its transitive Grails plugins) then check out: http://stackoverflow.com/questions/28357244/cobertura-coverage-for-grails-plugins-and-dependencies/28378265#28378265
This all assumes that your Grails app has tests which exercise the code in these plugins. The proper way to package your tests of course is to have them sitting in each plugin. I am about to refactor and do this soon.
Feel free to resolve this issue immediately, or delete it if you find it bothersome. :)