Testing with session

Just to be clear: I'm not a newbie with basic questions (I actually teach PHP and answer those basic questions all day long).

So first, your code should be:

PHP Code:

if (!isset($_SESSION))
{
    session_start();
} 


Second, according to the PHP manual, session_start() "Start new or resume existing session", which means I wouldn't even need the if as calling that function is idempotent.

Third, thank you for telling me I should use session_start(), but as you may have read in my question, I am in the testing context, within CodeIgniter. I very well know how to start a session, my question is where? In what class? What method? Maybe in a constructor? Or as a protected attribute? Do I change something in .env?

Thank you for reading the question properly before answering.