How can design errors be avoided when using $_SESSION['test'] in PHP functions?

Design errors when using $_SESSION['test'] in PHP functions can be avoided by ensuring that the $_SESSION variable is properly initialized at the beginning of the script or function. This can be achieved by starting the session using session_start() before accessing or modifying the $_SESSION variable. Failing to do so may result in unpredictable behavior or errors.

<?php
session_start();

function myFunction() {
    if(!isset($_SESSION['test'])) {
        $_SESSION['test'] = 'value';
    }

    // Rest of the function code
}

myFunction();
?>