The test checks the basic opt:tree features.

>>>>templates/test.tpl
<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
<opt:root>
<opt:tree name="tree">
<opt:list>
LIST START:
<opt:content />
LIST END:
</opt:list>
<opt:node>
NODE {$tree.title} START:
<opt:content />
NODE {$tree.title} END
</opt:node>
</opt:tree>
</opt:root>

>>>>expected.txt
OUTPUT

>>>>result.txt
LIST START:
NODE Main category 1 START:
NODE Main category 1 END
NODE Main category 2 START:
LIST START:
NODE Subcategory 2.1 START:
NODE Subcategory 2.1 END
LIST END:
NODE Main category 2 END
NODE Main category 3 START:
LIST START:
NODE Subcategory 3.1 START:
LIST START:
NODE Item 3.1.1 START:
NODE Item 3.1.1 END
NODE Item 3.1.2 START:
NODE Item 3.1.2 END
NODE Item 3.1.3 START:
NODE Item 3.1.3 END
LIST END:
NODE Subcategory 3.1 END
NODE Subcategory 3.2 START:
NODE Subcategory 3.2 END
NODE Subcategory 3.3 START:
LIST START:
NODE Item 3.3.1 START:
NODE Item 3.3.1 END
LIST END:
NODE Subcategory 3.3 END
LIST END:
NODE Main category 3 END
NODE Main category 4 START:
LIST START:
NODE Subcategory 4.1 START:
LIST START:
NODE Item 4.1.1 START:
NODE Item 4.1.1 END
LIST END:
NODE Subcategory 4.1 END
LIST END:
NODE Main category 4 END
LIST END:

>>>>data.php
$view->tree = array(0 =>
	array('title' => 'Main category 1', 'depth' => 0),
	array('title' => 'Main category 2', 'depth' => 0),
	array('title' => 'Subcategory 2.1', 'depth' => 1),
	array('title' => 'Main category 3', 'depth' => 0),
	array('title' => 'Subcategory 3.1', 'depth' => 1),
	array('title' => 'Item 3.1.1', 'depth' => 2),
	array('title' => 'Item 3.1.2', 'depth' => 2),
	array('title' => 'Item 3.1.3', 'depth' => 2),
	array('title' => 'Subcategory 3.2', 'depth' => 1),
	array('title' => 'Subcategory 3.3', 'depth' => 1),
	array('title' => 'Item 3.3.1', 'depth' => 2),
	array('title' => 'Main category 4', 'depth' => 0),
	array('title' => 'Subcategory 4.1', 'depth' => 1),
	array('title' => 'Item 4.1.1', 'depth' => 2)
);