public function updateLastTimestamp(ITestMessage $payload, Mage_Core_Model_Store $store)
    {
        list($scope, $scopeId) = $this->getScopeForStoreSettings($store);
        return Mage::getModel('core/config_data')
            ->addData(array(
                'path' => $this->_amqpConfigMap->getPathForKey('last_test_message_timestamp'),
                'value' => $payload->getTimestamp()->format(self::TIMESTAMP_FORMAT),
                'scope' => $scope,
                'scope_id' => $scopeId,
            ))
            ->save();
    }