public function testIsLeaf()
{
$this->assertTrue($this->clusters('Child 1')->isLeaf());
$this->assertTrue($this->clusters('Child 2.1')->isLeaf());
$this->assertTrue($this->clusters('Child 3')->isLeaf());
$this->assertTrue($this->clusters('Root 2')->isLeaf());
$this->assertFalse($this->clusters('Root 1')->isLeaf());
$this->assertFalse($this->clusters('Child 2')->isLeaf());
$new = new Cluster();
$this->assertFalse($new->isLeaf());
}