Using Whoops Error Handler

Hi,

I've manage to installed Whoops in CI 3 using composer, with addition to index.php like so.

Code:

switch (ENVIRONMENT)
{
    case 'development':
        error_reporting(-1);
        ini_set('display_errors', 1);
        error_reporting(E_ALL & ~E_NOTICE & ~E_DEPRECATED & ~E_STRICT & ~E_USER_NOTICE & ~E_USER_DEPRECATED);

        $whoops = new \Whoops\Run;
        $whoops->pushHandler(new \Whoops\Handler\PrettyPageHandler());
        $whoops->register();

                throw new Exception('whoops handler test'); // For testing purpose
        break;

    case 'testing':
                // Omitted
        break;

    case 'production':
                // Omitted
        break;

    default:
                // Omitted
        exit(1);
}

It works when there is an error or exception in index.php, but when error occurred in Controller or Model. CI standard error handler is still used, anyone ever successfully installed Whoops?