ModulesTest.java creates a directory and files in the system temp directory:

cat -n jdk/test/java/util/ServiceLoader/ModulesTest.java
  [...]
   240 Path jar = Files.createTempDirectory("lib").resolve("pearscript.jar");

These files are not cleaned up later.

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