--- /dev/null
+#!/usr/bin/perl
+
+use strict;
+use warnings;
+
+use Test::More tests => 34;
+use Test::Exception;
+
+use Scalar::Util 'isweak';
+
+BEGIN {
+ use_ok('Moose');
+}
+
+{
+ package BinaryTree;
+ use Moose;
+
+ has 'node' => (is => 'rw', isa => 'Any');
+
+ has 'parent' => (
+ is => 'rw',
+ isa => 'BinaryTree',
+ predicate => 'has_parent',
+ weak_ref => 1,
+ );
+
+ has 'left' => (
+ is => 'rw',
+ isa => 'BinaryTree',
+ predicate => 'has_left',
+ lazy => 1,
+ default => sub { BinaryTree->new(parent => $_[0]) },
+ );
+
+ has 'right' => (
+ is => 'rw',
+ isa => 'BinaryTree',
+ predicate => 'has_right',
+ lazy => 1,
+ default => sub { BinaryTree->new(parent => $_[0]) },
+ );
+
+ before 'right', 'left' => sub {
+ my ($self, $tree) = @_;
+ $tree->parent($self) if defined $tree;
+ };
+
+ __PACKAGE__->meta->make_immutable(debug => 0);
+}
+
+my $root = BinaryTree->new(node => 'root');
+isa_ok($root, 'BinaryTree');
+
+is($root->node, 'root', '... got the right node value');
+
+ok(!$root->has_left, '... no left node yet');
+ok(!$root->has_right, '... no right node yet');
+
+ok(!$root->has_parent, '... no parent for root node');
+
+# make a left node
+
+my $left = $root->left;
+isa_ok($left, 'BinaryTree');
+
+is($root->left, $left, '... got the same node (and it is $left)');
+ok($root->has_left, '... we have a left node now');
+
+ok($left->has_parent, '... lefts has a parent');
+is($left->parent, $root, '... lefts parent is the root');
+
+ok(isweak($left->{parent}), '... parent is a weakened ref');
+
+ok(!$left->has_left, '... $left no left node yet');
+ok(!$left->has_right, '... $left no right node yet');
+
+is($left->node, undef, '... left has got no node value');
+
+lives_ok {
+ $left->node('left')
+} '... assign to lefts node';
+
+is($left->node, 'left', '... left now has a node value');
+
+# make a right node
+
+ok(!$root->has_right, '... still no right node yet');
+
+is($root->right->node, undef, '... right has got no node value');
+
+ok($root->has_right, '... now we have a right node');
+
+my $right = $root->right;
+isa_ok($right, 'BinaryTree');
+
+lives_ok {
+ $right->node('right')
+} '... assign to rights node';
+
+is($right->node, 'right', '... left now has a node value');
+
+is($root->right, $right, '... got the same node (and it is $right)');
+ok($root->has_right, '... we have a right node now');
+
+ok($right->has_parent, '... rights has a parent');
+is($right->parent, $root, '... rights parent is the root');
+
+ok(isweak($right->{parent}), '... parent is a weakened ref');
+
+my $left_left = $left->left;
+isa_ok($left_left, 'BinaryTree');
+
+ok($left_left->has_parent, '... left does have a parent');
+
+is($left_left->parent, $left, '... got a parent node (and it is $left)');
+ok($left->has_left, '... we have a left node now');
+is($left->left, $left_left, '... got a left node (and it is $left_left)');
+
+ok(isweak($left_left->{parent}), '... parent is a weakened ref');
+