Adding test for the tree printer

src/Collection/Iterator/TreePrinter.php

@@ -0,0 +1,68 @@
+<?php
+/**
+ * CakePHP(tm) : Rapid Development Framework (http://cakephp.org)
+ * Copyright (c) Cake Software Foundation, Inc. (http://cakefoundation.org)
+ *
+ * Licensed under The MIT License
+ * For full copyright and license information, please see the LICENSE.txt
+ * Redistributions of files must retain the above copyright notice.
+ *
+ * @copyright     Copyright (c) Cake Software Foundation, Inc. (http://cakefoundation.org)
+ * @link          http://cakephp.org CakePHP(tm) Project
+ * @since         3.0.0
+ * @license       MIT License (http://www.opensource.org/licenses/mit-license.php)
+ */
+namespace Cake\Collection\Iterator;
+
+use Cake\Collection\Collection;
+use Cake\Collection\CollectionTrait;
+use Cake\Collection\Iterator\TreePrinter;
+use RecursiveIteratorIterator;
+
+/**
+ * Iterator for flattening elements in a tree structure while adding some
+ * visual markers for their relative position in the tree
+ *
+ */
+class TreePrinter extends RecursiveIteratorIterator {
+
+	use CollectionTrait;
+
+	protected $_key;
+
+	protected $_value;
+
+	protected $_current;
+
+	public function __construct($items, $valuePath, $keyPath, $spacer, $mode = RecursiveIteratorIterator::SELF_FIRST) {
+		parent::__construct($items, $mode);
+		$this->_value = $this->_propertyExtractor($valuePath);
+		$this->_key = $this->_propertyExtractor($keyPath);
+		$this->_spacer = $spacer;
+	}
+
+	public function key() {
+		$extractor = $this->_key;
+		return $extractor($this->_fetchCurrent(), parent::key(), $this);
+	}
+
+	public function current() {
+		$extractor = $this->_value;
+		$current = $this->_fetchCurrent();
+		$spacer = str_repeat($this->_spacer, $this->getDepth());
+		return $spacer . $extractor($current, parent::key(), $this);
+	}
+
+	public function next() {
+		parent::next();
+		$this->_current = null;
+	}
+
+	protected function _fetchCurrent() {
+		if ($this->_current !== null) {
+			return $this->_current;
+		}
+		return $this->_current = parent::current();
+	}
+
+}