Testing cron jobs in Magento

At first, find out how the cronjob is called from the module's config.xml by looking at the /config/crontab/jobs/*/run/model XPath, eg:

<config>
  ...
  <crontab> 
    <jobs> 
      <my_cronjob>
        <run>
          <model>my_cronjob/observer::my_method</model>
        </run>
        ...

On this example, you need to initialize the my_cronjob/observer model and call the method my_method on it. In order to do this create a file to run from command line with these contents:

<?php
// initialize magento application
require_once '/path/to/app/Mage.php';    
Mage::app();

// initialize model and run the method
$myCronJob = Mage::getModel('my_cronjob/observer');
$myCronJob->my_method();