Piwik\Plugins\CustomPiwikJs\File::checkWritable PHP Method

    public function checkWritable()
    {
        if (!$this->hasWriteAccess()) {
            throw new AccessDeniedException(sprintf('The file %s is not writable', $this->file));
        }
    }

 public function checkWillSucceed()
 {
     $this->fromFile->checkReadable();
     $this->toFile->checkWritable();
 }