class Serial:
    def __init__(self, port=None, baudrate=None, timeout=None):
        pass

    def reset_output_buffer(self):
        pass

    def reset_input_buffer(self):
        pass

    def writable(self):
        return True

    def write(self, bytes):
        pass

    def flush(self):
        pass

    def readline(self):
        return b"DONE\r\n"
