private function checkNewVersionIsValid()
{
// creating a Phar instance for an existing file is not allowed
// when the Phar extension is in readonly mode
if (!ini_get('phar.readonly')) {
// test the phar validity
$phar = new \Phar($this->newInstallerFile);
// free the variable to unlock the file
unset($phar);
}
return $this;
}