I'm trying to create a mock model for my controllers to use, but doesn't seem to be working

<?php

class QuestionsControllerTest extends TestCase {

    protected $questionMock;

    public function setUp()
    {
        $this->questionMock = Mockery::mock('Question');
    }

    public function testQuestionIndex()
    {
        $this->questionMock
           ->shouldReceive('latest')
           ->once();
        
        $this->app->instance('Question', $this->questionMock);

        $this->call('GET', 'questions');
    }
...

Below is my controller:

<?php namespace App\Http\Controllers;

use App\Http\Requests\QuestionRequest;
use App\Http\Controllers\Controller;

use App\Question;

use Auth;
use Request;

class QuestionsController extends Controller {

    protected $question;

    public function __construct(Question $question)
    {
        $this->question = $question;
    }

    public function index()
    {
        $questions = $this->question->latest()->get();
    
        return view('questions.index', compact('questions'));
    }
...

However, I get the following error:

$ ./vendor/bin/phpunit tests/controllers/QuestionsControllerTest.php 
PHPUnit 4.5.0 by Sebastian Bergmann and contributors.

Configuration read from /var/www/qasystem-admin/phpunit.xml

E

Time: 135 ms, Memory: 12.50Mb

There was 1 error:

1) QuestionsControllerTest::testQuestionIndex
Mockery\Exception\InvalidCountException: Method latest() from Mockery_0__Question should be called
exactly 1 times but called 0 times.

/var/www/qasystem-admin/vendor/mockery/mockery/library/Mockery/CountValidator/Exact.php:36
/var/www/qasystem-admin/vendor/mockery/mockery/library/Mockery/Expectation.php:271
/var/www/qasystem-admin/vendor/mockery/mockery/library/Mockery/ExpectationDirector.php:120
/var/www/qasystem-admin/vendor/mockery/mockery/library/Mockery/Container.php:296
/var/www/qasystem-admin/vendor/mockery/mockery/library/Mockery/Container.php:281
/var/www/qasystem-admin/vendor/mockery/mockery/library/Mockery.php:140
/var/www/qasystem-admin/tests/controllers/QuestionsControllerTest.php:15

What am I doing wrong? I'm worried that perhaps Laravel 5 is different, I can't really find much tutorials or documentation for testing on Laravel 5. The L5 docs doesn't really cover mocking models. Can anyone help? Thanks