silverstripe-frameworktest/code/tagfield/TestTag.php

<?php
if(class_exists('TagField')) {
	class TestTag extends DataObject {
		
		private static $db = array(
			'Title' => 'Text'
		);
		
		private static $belongs_many_many = array(
			'Pages' => 'TestTagFieldPage'
		);
		
		function requireDefaultRecords(){
			$class = $this->class;
			if(!DataObject::get_one($class)) {
				foreach(array('one', 'two', 'three', 'four') as $title) {
					$tag = new $class();
					$tag->Title = $title;
					$tag->write();
				}
				
			}
		}
	}
}