private function findNonExistingUserName()
    {
        for ($i = 0; $i < 20; ++$i) {
            $username = uniqid('User#', true);
            if (!$this->checkUserExistenceByUsername($username)) {
                return $username;
            }
        }

        throw new \Exception('Possible endless loop when attempting to find a new name for User.');
    }