This is the new load testing file: https://bitbucket.org/rbraakman/etherpad-stresstest

BELOW is the original load testing file.

This load tester is extremely useful for testing how many dormant clients can connect to etherpad.  

TODO:
Emulate characters being typed into a pad

HOW TO USE (from @mjd75) proper formatting at: https://github.com/ether/etherpad-lite/issues/360

Server 1:
Installed Node.js (etc), EtherPad and MySQL

Server 2:
Installed Xvfb and PhantomJS

I installed Xvfb following (roughly) this guide: http://blog.martin-lyness.com/archives/installing-xvfb-on-ubuntu-9-10-karmic-koala

    #sudo apt-get install xvfb
    #sudo apt-get install xfonts-100dpi xfonts-75dpi xfonts-scalable xfonts-cyrillic

Launched two instances of Xvfb directly from the terminal:

    #Xvfb :0 -ac
    #Xvfb :1 -ac

I installed PhantomJS following this guide: http://code.google.com/p/phantomjs/wiki/Installation

    #sudo add-apt-repository ppa:jerome-etienne/neoip
    #sudo apt-get update
    #sudo apt-get install phantomjs

I created a small JavaScript file for PhatomJS to use to control the browser instances:

### BEGIN JAVASCRIPT ###

var page = new WebPage(),
    t, address;

if (phantom.args.length === 0) {
    console.log('Usage: loader.js <some URL>');
    phantom.exit();
} else {
    t = Date.now();
    address = phantom.args[0];

    var page = new WebPage();
    page.onResourceRequested = function (request) {
        console.log('Request ' + JSON.stringify(request, undefined, 4));
    };
    page.onResourceReceived = function (response) {
        console.log('Receive ' + JSON.stringify(response, undefined, 4));
    };
    page.open(address);

}

### END JAVASCRIPT ###

And finally a launcher script that uses screen to run 400 instances of PhantomJS with the above script:

### BEGIN SHELL SCRIPT ###

#!/bin/bash     

# connect 200 instances to display :0                                                             
for i in {1..200}
do
  DISPLAY=:0 screen -d -m phantomjs loader.js http://ec2-50-17-168-xx.compute-1.amazonaws.com:9001/p/pad2 && sleep 2
done

# connect 200 instances to display :1                                                             
for i in {1..200}
do
  DISPLAY=:1 screen -d -m phantomjs loader.js http://ec2-50-17-168-xx.compute-1.amazonaws.com:9001/p/pad2 && sleep 2
done

### END SHELL SCRIPT ###