public function testRootsStatic()
{
$query = Cluster::whereNull('parent_id')->get();
$roots = Cluster::roots()->get();
$this->assertEquals($query->count(), $roots->count());
$this->assertCount(2, $roots);
foreach ($query->lists('id') as $node) {
$this->assertContains($node, $roots->lists('id'));
}
}
