Why does Test::MockObject make thawing my objects throw warnings?

Question

This one needs a bit of explanation to start with. I've got a unit test where I save Class::Std::Fast::Storable objects that come from SOAP::WSDL using Storable. The object I am storing is the result of a webservice call. It ends up being encoded with MIME::Base64 and written somewhere to a file. This is working great.

When I was building up the unit test, I needed to use Test::MockObject to mock the call that webservice, thus returning the restored object. But somehow this is throwing a bunch of warnings about the use of uninitialized value in hash element.

I tried recreating it as a small example. This first bit of code is how I get the base64 output for the example. We will use it in a minute.

use strict;
use warnings;
use MIME::Base64;
use Storable;
use SOAP::WSDL::XSD::Typelib::Builtin::anySimpleType;

my $object = SOAP::WSDL::XSD::Typelib::Builtin::anySimpleType->new;
$object->set_value('foo');
print encode_base64(Storable::freeze($object));

So we got three lines of base64. Let's try to restore them:

use strict;
use warnings;
use MIME::Base64;
use Storable;
use Test::Simple tests => 1;

local $/ = undef;
my $object = Storable::thaw(decode_base64(<DATA>));
ok( $object->get_value, 'foo' );

__DATA__
BAgIMTIzNDU2NzgECAgIE0ADAQAAAAQDAQAAAAoDZm9vBQAAAHZhbHVlMAAAAFNPQVA6OldTREw6
OlhTRDo6VHlwZWxpYjo6QnVpbHRpbjo6YW55U2ltcGxlVHlwZYAwU09BUDo6V1NETDo6WFNEOjpU
eXBlbGliOjpCdWlsdGluOjphbnlTaW1wbGVUeXBlEAQICDEyMzQ1Njc4BAgICAUBAAAAAQ==

Neat. It works!

~> perl foo.t
1..1
ok 1 - foo

Now let's add Test::MockObject.

use strict;
use warnings;
use MIME::Base64;
use Storable;
use Test::Simple tests => 1;
use Test::MockObject; # <------- only line I changed

local $/ = undef;
my $object = Storable::thaw(decode_base64(<DATA>));
ok( $object->get_value, 'foo' );

__DATA__
BAgIMTIzNDU2NzgECAgIE0ADAQAAAAQDAQAAAAoDZm9vBQAAAHZhbHVlMAAAAFNPQVA6OldTREw6
OlhTRDo6VHlwZWxpYjo6QnVpbHRpbjo6YW55U2ltcGxlVHlwZYAwU09BUDo6V1NETDo6WFNEOjpU
eXBlbGliOjpCdWlsdGluOjphbnlTaW1wbGVUeXBlEAQICDEyMzQ1Njc4BAgICAUBAAAAAQ==

Ok, this is weird. It works, but it throws an error.

1..1
Use of uninitialized value in hash element at /usr/lib/perl5/site_perl/5.16.2/SOAP/WSDL/XSD/Typelib/Builtin/anySimpleType.pm line 53, <DATA> chunk 1.
ok 1 - foo

So I looked at line 53 of anySimpleType.pm, and it says:

my $OBJECT_CACHE_REF = Class::Std::Fast::OBJECT_CACHE_REF();

sub new {
    my $self = pop @{ $OBJECT_CACHE_REF->{ $_[0] } }; # <-- here
    $self = bless \(my $o = Class::Std::Fast::ID()), $_[0]
        if not defined $self;

Hmm. $_[0] is undef. Looks like new was called without an argument.

But how the hell can loading Test::MockObject do that? Or maybe that warning is always popping up, but somehow it was not shown before? I debugged it a little, and it turns out the warning is always showing in Komodo IDEs debugger, regardless of what I loaded.

However, it only shows up in the normal program output if I have Test::MockObject loaded as well. Can anyone explain that to me?

Answer 1

I still don't know why this is happening exactly. My debugging led me to believe that the initialization warnings are always thrown by these Storable objects. However, they are silent if Test::MockObject is not there.

So the workaround to get it to shut up is as follows:

local $SIG{__WARN__} = sub { warn $_[0] unless $_[0] =~ /uninitialized/};
local $/ = undef;
my $object = Storable::thaw(decode_base64(<DATA>));
ok( $object->get_value, 'foo' );