bug#33195: 27.0.50; user-login-name has no group-login-name

[Eli Zaretskii <eliz@gnu.org>]

> From: Glenn Morris <rgm@gnu.org>
> Cc: Eli Zaretskii <eliz@gnu.org>,  33195@debbugs.gnu.org
> Date: Sat, 10 Nov 2018 13:36:47 -0500
> 
> Jules Tamagnan wrote:
> 
> > I've tried my hand at writing a test for this but am dubious it will
> > pass on all machines, I believe it should work on gnu/linux
> [...]
> > +(ert-deftest group-name ()
> > +  (let ((list `((0 . "root")
> > +                (1000 . ,(user-login-name 1000))
> > +                (1212345 . nil))))
> > +    (dolist (test list)
> > +      (should (equal (group-name (car test)) (cdr test))))))
> 
> This assumes that user 1000's primary group is the same as their login name.
> This is not at all guaranteed, so I will remove it.
> Eg it fails for me on rhel 7.5, and also on hydra.nixos.org, ref
> https://hydra.nixos.org/eval/1488740
> 
> I guess that UID 0 is always the root group, but I wouldn't swear to it.
> The 1212345 thing relies on UID 1212345 not existing.
> It seems to me that this is fragile too.
> So all in all, I'm not sure this test is very useful.

Maybe all platforms should use the same code as MS-Windows for this
test, then.