I have a Windows-only module on CPAN (exact opposite of your case) but I do the "same", test if it's Windows and then the version of Windows. I do it in the Makefile.PL since the module is completely useless on *nix:

# Only supported on Win32
unless ($^O eq "MSWin32" || $^O eq "cygwin") {
    die "OS unsupported\n"
}

# Must be Win32 version greater than 5
#   _WIN32_WINNT must be defined as greater than 5 for 
#   LockWorkStation prototype to be defined in winuser.h.
my $ver = `ver`;
$ver =~ / ([\d\.]+)/;
$ver = $1;

if ($ver < 5) {
    die "OS unsupported\n  Windows version must be greater than 5.\n  
+Found '$ver' with the 'ver' command."
}

WriteMakefile(
[...]
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If you don't want to preemptive test in the Makefile.PL, you can use SKIP in the tests after determining OS is Windows to skip over tests that won't make sense / fail.

OK, skip looks like what I want, but it results in something I don't understand. Here's a bare-bones example that causes the curios behavior:

#!/usr/bin/perl -w
use strict;
use Test;
BEGIN { plan tests => 1 };
skip (0, sub { ok(1) } );

I thought that would produce a single "ok", but here's the actual output:

1..1
# Running under perl version 5.018002 for linux
# Current time local: Tue Dec 30 00:51:18 2014
# Current time GMT:   Tue Dec 30 05:51:18 2014
# Using Test.pm version 1.26
ok 1
ok 2

Why are there two ok's?

If I change that first param to 1, so that it skips the test, it outputs one ok:

1..1
# Running under perl version 5.018002 for linux
# Current time local: Tue Dec 30 00:54:55 2014
# Current time GMT:   Tue Dec 30 05:54:55 2014
# Using Test.pm version 1.26
ok 1 # skip

???

Why are there two ok's?

One from skip the other from the ok? Probably true :)

If I change that first param to 1, so that it skips the test, it outputs one ok: ???

So what does the documentation for skip say?

Try see here https://metacpan.org/pod/Test#skip-skip_if_true-args

What does the cpan testers wiki say?

IIRC Devel::AssertOS

update: http://wiki.cpantesters.org/wiki/CPANAuthorNotes "How can I indicate that my distribution only works on a particular operating system?"

# in a Makefile.PL or Build.PL
use lib 'inc';
use Devel::AssertOS qw(Linux FreeBSD Cygwin);
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I do want to say, I've seen once or twice these types of tests used because of a dependence on /bin/gzip or some typical unix program ... they do exist on windows also :) so test for the program if thats the real dependency