如何使用代码模拟内部测试函数的方法

Question

I'm just trying to implement unit testing to my PHP application and really can't figure out how it works with mock/stub and Codeception

So I'm using Laravel and want to add testing to an API endpoint like this

$I->sendGET('/user/inventory/<user_id>');

Then in the controller I have function to authenticate the user, something like

public function getUserInventory($userId) {

    if ($this->authenticateUser($userId)) 
    {
        do some logic...
        if ($success) {
            return $good_data;
        } else {
            return $bad_data;
        }
    } 
    return false;
}

authenticateUser function is not relevant to the test and I just want to mock the return to true or false so I can test the actual logic on whether it should return $good_data or $bad_data, is that possible?

I've tried to declare stub object before calling the sendGET function like this

Stub::make(
    'App\Http\Controllers\Controller',
    ['authenticateUser' => true],
    $this
);

$I->sendGET('/user/inventory/<user_id>');

but it doesn't seem to use the stub object inside the getUserInventory function when I ran the test.

Is there any way to use stub/mock method inside the $I->sendGET('/user/inventory/<user_id>'); test?

Hopefully my question make sense