my @tests = (
    [[2,7,11,15], 9, [0,1]],
    [[3,2,4], 6, [1,2]],
    [[3,3], 6, [0,1]],
);

for my $test (@tests) {
    is_deeply
        sort_arrayref(two_sum($test->[INPUT], $test->[TARGET])),
        $test->[EXPECTED];
}

sub sort_arrayref {
    my ($aref) = @_;

    return [ sort { $a <=> $b } @$aref ];
}