Testing Controller method that is not linked to any routes

So i am giving a sample of my controller and web.php file. controller { public function add() { //Method called via web.php } public function multiply() { //how to access this while testing } }

web.php
route::get('/add','controller@add');

And now if i want to perform unit testing
case1: 
   add
    $response = $this->get(route('add'));
    Now it will send a get request when /add is accessed and controller method add will be accessed. And then i can use various assertions to check its functionality.

case2:
   multiply
   Here there isnt any route specified, so it wont be able to access controller method.

How can i test my multiply method in such a case