Maybe try to use Test::YAML::Meta to verify it locally.

Thanks. I have tested with Test::YAML::Meta and Test::YAML::Valid and it confirms that there is a problem with my META.yml. However it does not pinpoint what the problem is, nor how it got generated incorrectly. Thus I am still stuck. Also curiously the problem seems to be identified by YAML::Syck but not straight YAML.

Edit: Just to make this clear. If I run this code:

use strict;
use warnings;
use Test::More;

use Test::YAML::Valid qw(-Syck);
yaml_file_ok('META.yml', 'META.yml is YAML');
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it indicates that the YAML is invalid. If I remove the "-Syck" it's okay. If I run it on other META.yml it's okay. I find this very puzzling as it suggests not just that there is something mysteriously wrong with my YAML, but that Syck is not that transparent.

$ perl -MDDS  -mYAML::Syck -le 'Dump( YAML::Syck::LoadFile( shift))' M
+ETA.yml

Syck parser (line 4, column 62): syntax error ...
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line 4, column 62 is the abstract

abstract:           Test library that can be run in two modes: once to
+ generate outputs and secondly to compare against them
----------------------------------------------------------62-^
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Looks like a bug in ExtUtils::MakeMaker, it doesn't quote abstract properly.

Do you mind a mini-review of your code?

To get your SYNOPSIS POD to render as code, you should indent as follows:

=head1 SYNOPSIS

    use Test::Regression;
    ok_regression(sub {return "hello world"}, "t/out/hello_world.txt")
+;
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You should explicitly mention that TEST_REGRESSION_GEN is an environment variable:

If the TEST_REGRESSION_GEN environment variable is set to a true value
[download]

Additionally, I recommend adding a DESCRIPTION section to briefly discuss why someone would use your module. How would I distinguish it from the other CPAN Test modules? Does it complement other Test modules?

Thanks. I have updated the code in github as you can see http://github.com/periapt/test-regression/blob/master/lib/Test/Regression.pm.

$ wget http://cpansearch.perl.org/src/SILASMONK/Test-Regression-0.03/M
+ETA.yml

$ perl -MDDS  -mYAML -le'Dump( YAML::LoadFile( shift))' META.yml
$HASH1 = {
           abstract   => 'Test library that can be run in two modes: o
+nce to generate outputs and secondly to compare against them',
           author     => [ 'Nicholas Bamber <nicholas@periapt.co.uk>' 
+],
           build_requires
                      => { "ExtUtils::MakeMaker" => 0 },
           configure_requires
                      => { "ExtUtils::MakeMaker" => 0 },
           distribution_type
                      => 'module',
           generated_by
                      => 'ExtUtils::MakeMaker version 6.54',
           license    => 'perl',
           "meta-spec"
                      => {
                           url     => 'http://module-build.sourceforge
+.net/META-spec-v1.4.html',
                           version => 1.4
                         },
           name       => 'Test-Regression',
           no_index   => { directory => [
                           't',
                           'inc'
                         ] },
           requires   => {
                           "Algorithm::Diff"   => 0,
                           "Test::Differences" => 0,
                           "Test::More"        => 0,
                           "Text::Diff"        => 0
                         },
           version    => 0.03
         };

$ pmvers YAML
0.70
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1. An Example

   Maybe the following is of use..

   Here's an example of a Makefile.PL that helps generate a proper META.yml..

   use ExtUtils::MakeMaker;
   WriteMakefile(
      NAME => 'WordPress::XMLRPC',
      VERSION_FROM => 'lib/WordPress/XMLRPC.pm',
      PREREQ_PM => {
         'YAML' => 0,
         'SOAP::Lite' => 0,
         'XMLRPC::Lite' => 0,
         'Smart::Comments' => 0,
         'LEOCHARRE::Debug' => 0,
         'LEOCHARRE::CLI2' => 0,
      },
      LICENSE => 'perl',
      AUTHOR => 'Leo Charre leocharre at cpan dot org',
      ABSTRACT_FROM => 'lib/WordPress/XMLRPC.pod',
   
   );
   [download]

   The META.yml I get is..

   --- #YAML:1.0
   name:               WordPress-XMLRPC
   version:            1.21
   abstract:           api to wordpress xml rpc calls
   author:
       - Leo Charre leocharre at cpan dot org
   license:            perl
   distribution_type:  module
   configure_requires:
       ExtUtils::MakeMaker:  0
   requires:
       LEOCHARRE::CLI2:   0
       LEOCHARRE::Debug:  0
       Smart::Comments:   0
       SOAP::Lite:        0
       XMLRPC::Lite:      0
       YAML:              0
   no_index:
       directory:
           - t
           - inc
   generated_by:       ExtUtils::MakeMaker version 6.48
   meta-spec:
       url:      http://module-build.sourceforge.net/META-spec-v1.4.html
       version:  1.4
   [download]

   You can browse this in the distro WordPress::XMLRPC, also note the pod.

2. Checking What You're Getting..

   You can check what it's doing via the following.

   Once you have your distro,

   perl Makefile.PL
   make disttest
   

   # now look at the dir created mydistroname-vernum/META.yml and see if it's what you want.