DefineClassTest.java creates temporary directories for the test but does not clean them up later:

cat -n jdk/test/java/lang/invoke/DefineClassTest.java
   [...]
   168 Path dir1 = Files.createTempDirectory("classes");
   [...]
   174 Path dir2 = Files.createTempDirectory("classes");

The preferred approach would be to create temporary test files or directories under the jtreg property user.dir instead, if it is defined.

During a jtreg run, user.dir has the value $PWD/JTwork/scratch