Test::Prereq - check if Makefile.PL has the right pre-requisites


        # if you use Makefile.PL
        use Test::More;
        eval "use Test::Prereq";
        plan skip_all => "Test::Prereq required to test dependencies" if $@;

        # specify a perl version, test name, or module names to skip
        prereq_ok( $version, $name, \@skip );

        # if you use Module::Build
        use Test::More;
        eval "use Test::Prereq::Build";
        plan skip_all => "Test::Prereq::Build required to test dependencies" if $@;

        # or from the command line for a one-off check
        perl -MTest::Prereq -eprereq_ok

    #The prerequisites test take quite some time so the following construct is 
    #recommended for non-author testers
        use Test::More;
        eval "use Test::Prereq::Build";

        my $msg;
        if ($@) {
            $msg = 'Test::Prereq::Build required to test dependencies';
        } elsif (not $ENV{TEST_AUTHOR}) {
            $msg = 'Author test.  Set $ENV{TEST_AUTHOR} to a true value to run.';
        plan skip_all => $msg if $msg;


The prereq_ok() function examines the modules it finds in blib/lib/, blib/script, and the test files it finds in t/ (and It figures out which modules they use, skips the modules that are in the Perl core, and compares the remaining list of modules to those in the PREREQ_PM section of Makefile.PL.

If you use Module::Build instead, see Test::Prereq::Build instead.

Modules Test::Prereq can't find

Module::Info only tells Test::Prereq which modules you used, not which distribution they came in. This can be a problem for things in packages like libnet, libwww, Tk, and so on. At the moment Test::Prereq asks to expand anything in PREREQ_PM to see if one of the distributions you explicity list contains the module you actually used. This might fail in some cases. Please send me anything that does not do what you think it should.

Test::Prereq only asks for help if it needs it, since can be slow if it has to fetch things from the network. Once it fetches the right things, it should be much faster.

Problem with Module::Info

Module::Info appears to do something weird if a file it analyzes does not use (or require) any modules. You may get a message like

Can't locate object method "name" via package "B::NULL" at /usr/perl5.8.0/lib/site_perl/5.8.0/B/Module/ line 176.

Also, if a file cannot compile, Module::Info dumps a lot of text to the terminal. You probably want to bail out of testing if the files do not compile, though.

Problem with CPANPLUS

CPANPLUS apparently does some weird things, and since it is still young and not part of the Standard Library, Test::Prereq's tests do not do the right thing under it (for some reason). Test::Prereq cheats by ignoring CPANPLUS completely in the tests---at least until someone has a better solution. If you do not like that, you can set $EXCLUDE_CPANPLUS to a false value.

You should be able to do a 'make test' manually to make everything work, though.

Warning about redefining ExtUtils::MakeMaker::WriteMakefile

Test::Prereq has its own version of ExtUtils::MakeMaker::WriteMakefile so it can run the Makefile.PL and get the argument list of that function. You may see warnings about this.


prereq_ok( [ VERSION, [ NAME [, SKIP_ARRAY] ] ] )

Tests Makefile.PL to ensure all non-core module dependencies are in PREREQ_PM. If you haven't set a testing plan already, prereq_ok() creates a plan of one test.

If you don't specify a version, prereq_ok assumes you want to compare the list of prerequisite modules to the version of perl running the test.

Valid versions come from Module::CoreList (which uses $]).

        use Module::CoreList;
        print map "$_\n", sort keys %Module::CoreList::version;

prereq_ok attempts to remove modules found in lib/ and libraries found in t/ from the reported prerequisites.

The optional third argument is an array reference to a list of names that prereq_ok should ignore. You might want to use this if your tests do funny things with require.

Versions prior to 1.038 would use to virtually include prerequisites in distributions that you declared explicitly. This isn't really a good idea. Some modules have moved to different distributions, so you should just specify all the modules that you use instead of relying on a particular distribution to provide them. Not only that, expanding distributions with takes forever.

If you want the old behavior, set the TEST_PREREQ_EXPAND_WITH_CPAN environment variable to a true value.


* set up a couple fake module distributions to test

* warn about things that show up in PREREQ_PM unnecessarily


This source is in Github:


Many thanks to:

Andy Lester, Slavin Rezić, Randal Schwartz, Iain Truskett, Dylan Martin


brian d foy, <>


Copyright 2002-2014, brian d foy, All rights reserved

This software is available under the same terms as perl.