Check for root under Cygwin

[vsespb]

I have unit tests, which check that my code properly handle "permission denied" errors and other IO errors.
My application works only under POSIX systems (i.e. not Win32), and I am thinking now about porting it to CygWin.
Tests look like this (simplified version):

use strict;
use warnings;
use Test::More tests => 2;

my $file = 'somefile.tmp';
unlink $file;
open my $f, '>', $file; close $f;
chmod 0000, $file;

SKIP: {
 skip "cannot run under root", 2 unless $<;
 ok ! eval { somefunc($file); 1; };
 ok $@ =~ /cannot open file/;
}

unlink $file;

and somefunc() looks like this:

sub somefunc { open my $f, "<", shift or die 'cannot open file' };

(that is a simplified version too - just for proof of concept)
In the test you can see

skip "cannot run under root", 2 unless $<;

That's because otherwise test will fail under root.
That check, however, is not working under Cygwin as expected.
And I am wondering how that code could be fixed under cygwin?
(note that I am aware of several file-system emulator modules, but I decided to stick with real filesystem, for now)