Google\Spreadsheet\CellFeed::getId PHP Method

    public function getId()
    {
        return $this->xml->id->__toString();
    }

 public function testGetId()
 {
     $feed = new CellFeed($this->getSimpleXMLElement("cell-feed"));
     $this->assertEquals("https://spreadsheets.google.com/feeds/cells/15L06yklgflGRDjnN-VvhGYOoVLCH40DJoW5fFiqSTc5U/od6/private/full", $feed->getId());
 }