[solved] Test question: how to exercise conditional module load?

[radiantmatrix]

I like to use Devel::Cover to make sure that my test suite adequately covers my code. I've run into a bit of a conundrum on how to test something.

BEGIN {
    eval { require YAML::Syck; YAML::Syck->import };  #1
    if ($@) {
        require YAML; YAML->import;                   #2
    }
}

Yes, I know I could use Best (use Best qw/YAML::Syck YAML/;), but for this project, it's not an option due to bureaucratic considerations.

My problem is that my tests only exercise the statements in #1, and not in #2 -- or vice-versa. I'm looking for a way that my test script can, e.g. temporarily make require YAML::Syck or YAML::Syck->import die so that I can automatically prove the fallback works.

I have tried to search for answers, but can't seem to find a set of search terms that provides any enlightenment. So, I turn to the Monestary: any ideas?

Updates:

• 20080617 : solved, thanks to a nice lead from Corion. See the solution post

[Corion]

You can always fake things in Perl:

$INC{YAML::Syck} = 1; # fake that YAML::Syck is loaded
sub YAML::Syck::import { die }; # but make the ->import call fail

require Your::Module;
# Now it will try to use YAML

You can also use my module, Test::Without::Module, but there are other modules as well for testing in the absence of modules.

[radiantmatrix]

Thanks! It didn't work quite perfectly as provided, but it was enough info to get me a working solution:

{
   local %INC;
   delete $INC{YAML.pm};      # make sure YAML isn't loaded
   $INC{'YAML/Syck.pm'} = 1;  # fake loading of YAML::Syck
   sub YAML::Syck::import { die }
   
   require My::Module;
   ok( $INC{'YAML.pm'}, 'YAML loaded when YAML::Syck not present' );
}

Thanks again!