On Feb 22, 2023, at 00:02, quiekaizam via 9fans <9fans@9fans.net> wrote:

Indeed, my test(1) doesn't seem to support such syntax. Is this a version problem?

I believe so, yes. It looks like 9front has made some significant changes to (or removed? I didn’t dig in) test’s handling of “implied” -a and -o operands. 

For comparison, see:
https://9p.io/sources/plan9/sys/src/cmd/test.c
http://git.9front.org/plan9front/plan9front/e6c6217b35c319127f0200fdb28ec86e1b774a4f/sys/src/cmd/test.c/f.html

I would suggest compiling the plan9 version locally and seeing if that fixes the issue.