Even shorter and faster (and most probably also memory efficient)

use strict;
use warnings;
use Test::More;

sub chunks {
    my $str   = "";
    while (my @cols = splice @_, 0, 3) {
        $str .= "@cols\n";
    }
    return $str;
}

#  ========= Tests

my @list = ("a", "bb", "c", "d", "e", "f", "g", "h");
my @old = @list;

my $text =
  "a bb c\n" .
  "d e f\n"  .
  "g h\n"
  ;


is( chunks(@list) => $text, "Rosetta's Example");

is( chunks() => "", "Empty string" );

is( chunks("") => "\n", "Empty List" );

is_deeply( \@list, \@old, "Non destructive! yeah ... :)");

done_testing;
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NB: @_ is a array of aliases, not an alias itself. Destryoing it doesn't affect the argument given :)