/**
* @test
* @expectedException \InvalidArgumentException
*/
public function throws_an_exception_when_adding_a_child_whose_name_already_exists_in_its_children()
{
$category = new Category();
$child = (new Category())->setTitle('foo');
$duplicate = (new Category())->setTitle('foo');
$category->addChild($child);
$category->addChild($duplicate);
}