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