- PDM provides now the reason of violation and also gives reason and URL...

... such as http://pmd.sourceforge.net/pmd-5.2.1/pmd-java/rules/java/unusedcode.html#UnusedLocalVariable

- checkstyle and findbugs do not offer such feature out of the box
Now I see. You don't need to unit-test severity conversion since you test whole rule conversion below.