silverstripe-framework/tests/php/Forms/FormScaffolderTest/ArticleExtension.php

<?php

namespace SilverStripe\Forms\Tests\FormScaffolderTest;

use SilverStripe\Dev\TestOnly;
use SilverStripe\Forms\FieldList;
use SilverStripe\Forms\TextField;
use SilverStripe\ORM\DataExtension;

class ArticleExtension extends DataExtension implements TestOnly
{
	private static $db = array(
		'ExtendedField' => 'Varchar'
	);

	public function updateCMSFields(FieldList $fields)
	{
		$fields->addFieldToTab('Root.Main',
			new TextField('AddedExtensionField')
		);
	}

}