Magento 2.2.6 | Uncaught Error: Undefined class constant ‘CACHE_TAG’

I am very new to Magento, i created a CRUD custom module, when I input some data in form, and hit save button, I got an error like this:

Fatal error: Uncaught Error: Undefined class constant 'CACHE_TAG' in C:\xampp\htdocs\test-local\app\code\Testing\SimpleNews\Model\News.php:9 Stack trace: #0 C:\xampp\htdocs\test-local\vendor\magento\framework\App\Cache\Tag\Strategy\Identifier.php(25):Testing\SimpleNew\Mode\News->getIdentities()  #1 C:\xampp\htdocs\test-local\vendor\magento\framework\App\Cache\Tag\Resolver.php(43): Magento\Framework\App\Cache\Tag\Strategy\Identifier->getTags(Object(Testing\SimpleNews\Model\News))  #2 C:\xampp\htdocs\test-local\vendor\magento\module-page-cache\Observer\FlushCacheByTags.php(64): Magento\Framework\App\Cache\Tag\Resolver->getTags(Object(Testing\SimpleNews\Model\News))  #3 C:\xampp\htdocs\test-local\vendor\magento\framework\Event\Invoker\InvokerDefault.php(72): Magento\PageCache\Observer\FlushCacheByTags->execute(Object(Magento\Framework\Event\Observer))  #4 C:\xampp\htdocs\test-local\vendor\magento\framework\Event\Invoker\InvokerDefault.php(60): Magento\Framework\Event\Invoker\InvokerDefault->_callObserverMethod(Object(Magento\ in C:\xampp\htdocs\test-local\app\code\Testing\SimpleNews\Model\News.php on line 9 

This is my htdocs\test-local\app\code\Testing\SimpleNews\Model\News.php code:

<?php  namespace Testing\SimpleNews\Model;  class News extends \Magento\Framework\Model\AbstractModel implements \Magento\Framework\DataObject\IdentityInterface {     public function getIdentities()     {         return [self::CACHE_TAG . '_' . $  this->getId()];     }      public function getDefaultValues()     {         $  values = [];          return $  values;     }      /**      * Define resource model      */     protected function _construct()     {         $  this->_init('Testing\SimpleNews\Model\Resource\News');     } }