Running jtreg with option "-show" gives me error messages (tried with multiple test directories):

thomas@mainframe:/shared/projects/openjdk/jtreg$ jtreg -show:System.out -jdk:<my-jdk> /shared/projects/openjdk/jdk-sandbox/source/test/hotspot/jtreg/runtime/Metaspace/
Directory "JTwork" not found: creating
More than one test specified
No test specified

If I omit the -show option, the tests run as expected.