Force the session to be saved and closed.
This method must invoke session_write_close() unless this interface is used for a storage object design for unit or functional testing where a real PHP session would interfere with testing, in which case it it should actually persist the session data if required.
Overrides MockArraySessionStorage::save
public function save() {
file_put_contents($this
->getFilePath(), serialize($this->data));
// this is needed for Silex, where the session object is re-used across requests
// in functional tests. In Symfony, the container is rebooted, so we don't have
// this issue
$this->started = false;
}