Demonstrates how to stub and test for collaborators in a class constructor using sinon and proxyquire. See https://github.com/sinonjs/sinon/issues/831

collaborator.js

module.exports = function(n){
    // do something with n
}

my-class.js

var Collab = require('./collaborator');
function MyClass(n){
    this.collabs = [];
    while(n--) this.collabs.push(new Collab(n));
}

module.exports = MyClass;

test.js

var assert = require('assert');
var sinon = require('sinon');
var proxyquire = require('proxyquire');

var stub = sinon.stub();
var MyClass = proxyquire('./my-class', { './collaborator' : stub });
var myClass = new MyClass(4);

assert.equal(stub.callCount,4);
assert.equal(stub.callCount,4);

assert(stub.firstCall.calledWith(3));
assert(stub.secondCall.calledWith(2));
assert(stub.getCall(2).calledWith(1));

assert(stub.getCall(3).calledWith(0));
assert(stub.getCall(3).calledWithNew());