crontab -e

*/1 * * * * /bin/sh /Applications/XAMPP/htdocs/mymagento/cron.sh

<config>
    ...
    <crontab>
        <jobs>
            <mynamespace_mymodule_test>
                <schedule><cron_expr>*/1 * * * *</cron_expr></schedule>
                <run><model>mymodule/observer::test</model></run>
            </mynamespace_mymodule_test>
        </jobs>
    </crontab>
    ...
</config>

class Mynamespace_Mymodule_Model_Observer {

    public function test(){
        error_log("success!!!!!");
    }
}