Testing and QA

Hello.
What I need to do is to check the user's grade for a specific quiz and if the grade is over 50, then the system should send him an email.

I added the following in mod/quiz/view.php (after line 177):

if ($mygrade >50) {
 send_email($user);    // I added this funtion in lib/moodlelib.php
}

but nothing seems to work.
Is something wrong with the user's authedication ?

Thank you in advance