> tree .
.
├── node_modules
├── src
│   └── utils.js
└── test
    └── utils.js

> cat src/utils.js
define(['underscore'], function () {

    "use strict";

    if ('function' !== typeof Object.beget) {
        Object.beget = function (o) {
            var f = function () {
            };
            f.prototype = o;
            return new f();
        };
    }

});

> cat test/utils.js
var requirejs = require('requirejs');
requirejs.config({nodeRequire: require});

requirejs(['../src/utils'], function(utils) {

    suite('utils', function() {
        test('should always work', function() {
            assert.equal(1, 1);
        })
    })

});

> mocha

node.js:201
        throw e; // process.nextTick error, or 'error' event on first tick
              ^
Error: Calling node's require("../src/utils") failed with error: ReferenceError: define is not defined
    at /.../node_modules/requirejs/bin/r.js:2276:27
    at Function.execCb (/.../node_modules/requirejs/bin/r.js:1872:25)
    at execManager (/.../node_modules/requirejs/bin/r.js:541:31)
    ...

> cat test/utils.js

var requirejs = require('requirejs');
requirejs.config({nodeRequire: require});

requirejs(['../src/utils', 'assert'], function(utils, assert) {

    suite('utils', function() {
        test('should always work', function() {
            assert.equal(1, 1);
        })
    })

});
> mocha -u tdd

  .

  ✔ 1 tests complete (1ms)

if(typeof require != 'undefined') {
    // Require server-side-specific modules
}

// Insert code here

if(typeof module != 'undefined') {
    module.exports = whateverImExporting;
}

mocha.addFile('lib/tests/Main_spec_node');

describe('Testing "Other"', function(done){
    var Other;
    beforeEach(function(done){
        requirejs(['lib/Other'], function(_File){
            Other = _File;
            done(); // #1 Other Suite will run after this is called
        });
    });

    describe('#1 Other Suite:', function(){
        it('Other.test', function(){
            chai.expect(Other.test).to.equal(true);
        });
    });
});

> cat $PROJECT_HOME/test/test.js

var requirejs = require('requirejs');
var path = require('path')
var project_directory = path.resolve(__dirname, '..')

requirejs.config({
  nodeRequire: require,
  paths: {
    'widget': project_directory + '/src/js/some/widget'
  }
});

describe("Mocha needs one test in order to wait on requirejs tests", function() {
  it('should wait for other tests', function(){
    require('assert').ok(true);
  });
});


requirejs(['widget/viewModel', 'assert'], function(model, assert){

  describe('MyViewModel', function() {
    it("should be 4 when 2", function () {
        assert.equal(model.square(2),4)
    })
  });

})

> cat $PROJECT_HOME/src/js/some/widget/viewModel.js

define(["knockout"], function (ko) {

    function VideModel() {
        var self = this;

        self.square = function(n){
            return n*n;
        }

    }

    return new VideModel();
})

if (typeof define !== 'function') {
    var define = require('amdefine')(module);
}

npm install amdefine

var root =  typeof exports !== "undefined" && exports !== null ? exports : window;

var foo = root.foo;
if (!foo && (typeof require !== 'undefined')) {
    foo = require('./foo');
}

var Bar = function() {
    // do something with foo
}

root.bar = Bar;