my $negated = qr{^(?!.*?$regex)}s;

##</code><code>##

#!/usr/bin/perl
use warnings;
use strict;
use Test::More qw(no_plan);

# first item:  regex
# second item: list of strings that regex should match
# third item:  list of strings that negated regex should match
my @r = (
    [qr{a},  ['a'],      ['', 'b']],
    [qr{^a}, [qw(a ab)], ['', 'b', 'ba']],
    [qr{a$}, [qw(a ba aba)], ['', 'b', 'ab']],
);

for (@r){
    my ($re, $pass, $fail) = @$_;
    my $negated = qr{^(?!.*?$re)};
    for (@$pass){
        like   $_, $re;
        unlike $_, $negated;
    }
    for (@$fail){
        like   $_, $negated;
        unlike $_, $re;
    }
}