private function validate()
    {
        $file = $this->file;

        if (!is_file($file)) {
            throw new \RuntimeException(sprintf("'%s' is not a file", $file));
        }

        if (!is_readable($file)) {
            // @codeCoverageIgnoreStart
            throw new \RuntimeException(sprintf("'%s' is not a readable file", $file));
            // @codeCoverageIgnoreEnd
        }
    }