The jtreg directive

@requires !vm.gc.Z

doesn not run the CompressedOops version of the test when ZGC is present in the VM that is running the test, even if -XX:+UseZGC is not passed on the command line.

On the other hand, using

@requires vm.gc != "Z"

Does run the compressed oops versions of the test unless -XX:+UseZGC is passed on the command line.

Maybe this is a bug in test/jtreg-ext/requires/VMProps.java ?