Does the set-up activity that ensures $(G.testfile) is a good choice also ensure that "$(G.testfile)*" don't exist ?

(Aside.) We fairly routinely have tests that need a "cannot possibly exist" file, such as this.  Ideally, this would be one that cannot exist even if weird stuff is happening on the host, e.g. our tests being run and going wrong.  It may thus make sense to have a $(G.nosuch) "directory" that we can use for this, e.g. /dev/tty/bork (because, if /dev/tty is a directory, everything is broken already).