testing for global variable in mocha js from node

I am new to js unit testing and I am trying to use mocha for my backbone contact manager. However, i have a global window.ContactManager variable that I want to test whether it exists. The variable looks like so:

window.ContactManager = {
    Models: {},
    Collections: {},
    Views: {},
    Routers: {}

    start: function(data) {

    }   
}

My test that does not work: var expect = require ('chai').expect;

describe("Application", function() {
    it('creates a global variable for the name space ContactManager' , function () {
        expect(ContactManager).to.exist;
    })
});

How do I test and access a global window variable existence in mocha from running the tests in the console?