chai-eventemitter 
This is a plugin for chai to simplify the testing of EventEmitter.
EventEmitters can be testing using spies, but they are rather heavyweight for most usecases:
var spy = sinon.spy()
ee.on('test', spy)
ee.emit('test')
expect(spy).to.have.been.called()
spy.reset()
ee.emit('test', args)
expect(spy).to.have.been.calledWith(args)
chai-eventemitter replaces this with something much more digestable:
expect(function(){ ee.emit('test') }).to.emitFrom(ee, 'test')
expect(function(){ ee.emit('test', arg) }).to.emitFrom(ee, 'test', arg)
Setup
node.js / io.js
var chai = require('chai')
chai.use(require('chai-eventemitter'))
Browser
<script src="chai.js"></script>
<script src="chai-eventemitter.js"></script>
License
chai-eventemitter is released under the MIT License