source: trunk/essentials/dev-lang/perl/ext/Storable/t/attach_singleton.t

#!./perl -w
#
#  Copyright 2005, Adam Kennedy.
#
#  You may redistribute only under the same terms as Perl 5, as specified
#  in the README file that comes with the distribution.
#

# Tests freezing/thawing structures containing Singleton objects,
# which should see both structs pointing to the same object.

sub BEGIN {
    if ($ENV{PERL_CORE}){
        chdir('t') if -d 't';
        @INC = ('.', '../lib');
    } else {
        unshift @INC, 't';
    }
    require Config; import Config;
    if ($ENV{PERL_CORE} and $Config{'extensions'} !~ /\bStorable\b/) {
        print "1..0 # Skip: Storable was not built\n";
        exit 0;
    }
}

use Test::More tests => 11;
use Storable ();

# Get the singleton
my $object = My::Singleton->new;
isa_ok( $object, 'My::Singleton' );

# Confirm (for the record) that the class is actually a Singleton
my $object2 = My::Singleton->new;
isa_ok( $object2, 'My::Singleton' );
is( "$object", "$object2", 'Class is a singleton' );

############
# Main Tests

my $struct = [ 1, $object, 3 ];

# Freeze the struct
my $frozen = Storable::freeze( $struct );
ok( (defined($frozen) and ! ref($frozen) and length($frozen)), 'freeze returns a string' );

# Thaw the struct
my $thawed = Storable::thaw( $frozen );

# Now it should look exactly like the original
is_deeply( $struct, $thawed, 'Struct superficially looks like the original' );

# ... EXCEPT that the Singleton should be the same instance of the object
is( "$struct->[1]", "$thawed->[1]", 'Singleton thaws correctly' );

# We can also test this empirically
$struct->[1]->{value} = 'Goodbye cruel world!';
is_deeply( $struct, $thawed, 'Empiric testing corfirms correct behaviour' );

# End Tests
###########

package My::Singleton;

my $SINGLETON = undef;

sub new {
        $SINGLETON or
        $SINGLETON = bless { value => 'Hello World!' }, $_[0];
}

sub STORABLE_freeze {
        my $self = shift;

        # We don't actually need to return anything, but provide a null string
        # to avoid the null-list-return behaviour.
        return ('foo');
}

sub STORABLE_attach {
        my ($class, $clone, $string) = @_;
        Test::More::ok( ! ref $class, 'STORABLE_attach passed class, and not an object' );
        Test::More::is( $class, 'My::Singleton', 'STORABLE_attach is passed the correct class name' );
        Test::More::is( $clone, 0, 'We are not in a dclone' );
        Test::More::is( $string, 'foo', 'STORABLE_attach gets the string back' );

        # Get the Singleton object and return it
        return $class->new;
}