public function store($data)
    {
        $this->cache[$this->testSessionId] = &$data;
        $encodedData = $this->getStorageFormat()->encode($data);
        
        $this->getStorageService()->set($this->getUserKey(), $this->getStorageKey(), $encodedData);
        \common_Logger::d(sprintf('QtiTimer: Stored %d bytes into state storage', strlen($encodedData)));

        return $this;
    }