Fatal error: Class 'Demo_Test_Helper_Data' not found in F:\wamp\www\magentodemo\app\Mage.php on line 546

Question

Please Help me what is my fault in set up of custom helper class in magento

Fatal error: Class 'Demo_Test_Helper_Data' not found in F:\wamp\www\magentodemo\app\Mage.php on line 546

Folder sturcture

config.xml

`<?xml version="1.0"?>
<config>
        <global>
                <models>
                        <test>
                            <class>Demo_Test_Model</class>
                        </test>
                </models>
                <blocks>
                        <test>
                            <class>Demo_Test_Block</class>
                        </test>
                </blocks>
                <helpers>
                        <test>
                            <class>Demo_Test_Helper</class>
                        </test>
                </helpers>
        </global>
</config>`

Data.php

`<?php
class Demo_Test_Helper_Data extends Mage_Core_Helper_Abstract{
}
?>`

In app/etc/modules/Data_Test.xml

`<?xml version="1.0"?>
<config>
        <modules>
                <Demo_Test>
                        <active>true</active>
                        <codePool>local</codePool>
                </Demo_Test>
        </modules>
</config>`

Call Helper class in test.php file From root directory

`<?php 
require_once "app/Mage.php";
Mage::app();
$helper = Mage::helper("test");
?>`

Answer 1

try to below config file.

<?xml version="1.0"?>
   <modules>
    <Demo_Test>
      <version>0.1.0</version>
    </Demo_Test>
  </modules>
  <config>
        <global>
                <models>
                        <test>
                            <class>Demo_Test_Model</class>
                        </test>
                </models>
                <blocks>
                        <test>
                            <class>Demo_Test_Block</class>
                        </test>
                </blocks>
                <helpers>
                        <test>
                            <class>Demo_Test_Helper</class>
                        </test>
                </helpers>
        </global>
</config>`