gistfile1.php

final class User extends AggregateRoot
{
    private $id;

    protected function getRules()
    {
        return [
            'id' => [UserId::class],
        ];
    }
}

final class UserStub
{
    public static function create(UserId $userId)
    {
        return new User(['id' => $userId]);
    }

    public static function random()
    {
        return static::create(UserIdStub::random());
    }
}