These two shared test classes do almost essentially the same thing:

test//lib/jdk/test/lib/classloader/ClassUnloadCommon.java

and

test/hotspot/jtreg/vmTestbase/nsk/share/ClassUnloader.java

The last one was recently fixed, where the first already had a similar fix, but they do mostly the same things. It would be good if the vmTestbase tests used the common class, which is used by several other runtime tests.