Insert the part from desc.xml to the module/plugin/template xml and create a folder field and copy the file testing.php inside it

desc.xml

				<field name="testone" class="" type="testone" default="0"
				       label="test one"
				       description="test one" />

testone.php

<?php
defined('JPATH_BASE') or die;

JFormHelper::loadFieldClass('list');

class JFormFieldTestOne extends JFormFieldList
{
	protected $type = 'TestOne';

	public function getOptions()
	{
		$x = array (
			0 => array(
				'value' => '0',
				'text' => 'test',
			),
			1 => array(
				'value' => '1',
				'text' => 'test',
			),
		);
		return array_merge(parent::getOptions(), $x);
	}
}