public function createFolder($parentFolderPath, $folderName)
    {
        $this->throwIfOperationNotInBaseFolder($parentFolderPath);

        $folderPath = $parentFolderPath . '/' . $folderName;

        $wasCreationSuccessful = mkdir($folderPath, 0777, true);
        if (!$wasCreationSuccessful) {
            throw new IOException("Unable to create folder: $folderPath");
        }

        return $folderPath;
    }