Others have answered your question, but I'd just like to point out that if you put a \b next to a non-word character, you're likely to get the exact opposite of what you want. That is, it will only match if the character next to it is a word character. So another way to fix it would be to use \B to assert that the character before you is also a non-word character.

#!/usr/bin/perl -l

use strict;
use warnings;

while(<DATA>){
  chomp;
  print;
  print /\b\@testing\b/ ? "Matched \\b" : "Did not match \\b";
  print /\B\@testing\b/ ? "Matched \\B" : "Did not match \\B";
  print "";
}

__DATA__
@testing
foo@testing
foo @testing
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