session - php $_SESSION got mixed -

i have question php $_session.

say have user enter index.php , put info,

$_session['info'] = usera 

now user b enter index.php , put other info,

$_session['info'] = userb 

now in test.php, when call

$info=$_session['info'] 

usera or userb?

thanks!!

if session same both users, user b overwrite user a's value.

if session different both users, value user logged in as.

if have no session, nothing.