If you execute the tests in jdk/test or hotspot/test and want to access the top-level testlibrary you use:

@library /../../test/lib

which resolves relative to where TEST.ROOT is and so finds the top-level test/lib directory.

However this also causes directory test/lib to be create in the current directory - which is part of the source tree - so we get jdk/test/test/lib. The created directory is empty and has no affect on the success or otherwise of the tests, but it should not be created.