I typically use typeglobs to override the sub and capture the arguments. Then, you can test whether or not carp was called and if it received the correct arguments. Below is a test script.

#!/usr/bin/perl -w
use strict;
package Foo;
use Carp;

sub bar {
    carp "This is a test";
}

package main;
use Test::More 'no_plan';
use constant MODULE => 'Foo';

{
  my $carp;
  local *Foo::carp = sub { $carp = join '', @_ };
  can_ok( MODULE, 'bar' );
  Foo::bar();
  ok( $carp, 'Calling Foo::bar() should call carp()' );
  is( $carp, 'This is a test', '... with the correct error message' );
}
[download]

Just make sure that you localize the typeglob. This ensures that subsequent calls to carp that you forgot to trap will still spit out error messages.

Cheers,
Ovid

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