#!/usr/bin/env perl

use strict;
use warnings;

my @data = (
    [[qw{a b}], [qw{a b}]],
    [[qw{a b}], [qw{a}]],
    [[qw{a b}], [qw{a b c}]],
    [[qw{a b}], [qw{b 99 xyz}]],
);

for (@data) {
    my @ref = @{$_->[0]};
    my @test = @{$_->[1]};
    print "REF: '@ref' TEST: '@test'\n";
    my ($only_in_ref, $not_in_ref) = compare(\@ref, \@test);
    print "Only in REF: @{[sort keys %$only_in_ref]}\n";
    print "Not in REF:  @{[sort keys %$not_in_ref]}\n";
    print '-' x 40, "\n";
}

sub compare {
    my ($ref, $test) = @_;

    my %only_in_ref = map +($_ => 1), @$ref;
    my %not_in_ref;

    for (@$test) {
        if (exists $only_in_ref{$_}) {
            delete $only_in_ref{$_};
        }
        else {
            ++$not_in_ref{$_};
        }
    }

    return (\%only_in_ref, \%not_in_ref);
}

##</code><code>##

REF: 'a b' TEST: 'a b'
Only in REF:
Not in REF:
----------------------------------------
REF: 'a b' TEST: 'a'
Only in REF: b
Not in REF:
----------------------------------------
REF: 'a b' TEST: 'a b c'
Only in REF:
Not in REF:  c
----------------------------------------
REF: 'a b' TEST: 'b 99 xyz'
Only in REF: a
Not in REF:  99 xyz
----------------------------------------