Nodeunit testing for serial communication

Question

I'm writing an npm module to interface with a piLite with node.js. I'd like to write it properly using TDD principles.

The code I need to test:

var SerialPort = require("serialport").SerialPort;

exports.PiLite = {
    device: "/dev/ttyAMA0",
    baudrate: 9600,
    client: null,
    init: function() {
        this.client = new SerialPort(this.device, {
            baudrate: this.baudrate
        }, false);
    },
    connect: function(callback) {
        this.init();

        this.client.open(function() {
          console.log('Connected to Pi Lite');

          callback();
        });
    },
    write: function (data) {
    ...

The standard usage would be:

var pilite = require('pilite').PiLite;

pilite.connect(function() {
    pilite.write('some data');
    // calls to functions to send messages to pilite
}

I understand how to test assertions but I don't see how I can test the connectivity to the serial port.

Should I test for it or just test the functions I'm using to write to the serial port?

Edit: I'm pretty new to Nodeunit so any pointers in the right direction would be great.