How to properly call laravel's middleware closure in phpunit?

How to properly call this middleware closure function in phpunit test so that $user will be set?

Auth::user is mocked and will receive the proper user object, but the function is not called when creating the controller instance.

Here is my code:

use App\Http\Controllers\Controller;

class CustomController extends Controller
{
    private $user;

    public function __construct()
    {
        $this->middleware(function ($request, $next) {
            $this->user = Auth::user();
            return $next($request);
        });
    }
}

via Chebli Mohamed