simple overrides for quick mocking in perl

A more concrete example (and one I use too frequently) of overriding for testing similar to what is described by Sawyer X at blogs.perl.org: Simple symbol overriding for tests. Of course, my example uses inheritance and re-blessing rather than symbol overriding, but the result is basically the same. I like to use the snippet below to test mail sending functionality by simply printing the resulting mail to stdout.

my $smtp = Net::SMTP->new($mailhost);
...
if ($i_dont_want_to_send_mail) {
  package Mock::SMTP;
  our @ISA = qw(Net::SMTP);

  no strict qw(refs);
  for (qw(mail to data dataend quit)) {
    *$_ = sub { };
  }

  for (qw(datasend)) {
    *$_ = sub { shift; print @_, "\n" }
  }

  # re-bless my Net::SMTP reference to a Mock reference
  $smtp = bless $smtp || {};
}