Module.js

function A() {
	return 'A1'+exports.B();
}
exports.A = A;

function B() {
	return 'B1';
}
exports.B = B;

function C() {
	return 'C1';
}
exports.C = C;

C.prototype.D = function() {
	return 'D1'+this.E();
}

C.prototype.E = function() {
	return 'E1';
}

var F = {
	G: function() {
		return 'G1'+F.H();
	},

	H: function() {
		return 'H1';
	}
}
exports.F = F;

exports.exports = exports;
console.log(F.G());

Test.js

var should = require('should');
var sinon = require('sinon');
require('sinon-mocha').enhance(sinon);
var util = require('util');
var DummyModule = require('../src/DummyModule');
var http = require('http');

describe('Dummy Module', function() {
	it('should be able to replace B1 with B2', function() {
		sinon.stub(DummyModule, 'B', function() {
			return 'B2';
		})

		should.equal(DummyModule.A(), 'A1B2');
	})

	it('should be able to replace A1 with A2', function() {

		sinon.stub(DummyModule, 'A', function() {
			return 'A2' + this.B();
		})

		should.equal(DummyModule.A(), 'A2B1');
	})

	it('should be able to replace A1 with A2 and B1 with B2', function() {
		sinon.stub(DummyModule, 'A', function() {
			return 'A2'+this.B();
		})

		sinon.stub(DummyModule, 'B', function() {
			return 'B2';
		})

		should.equal(DummyModule.A(), 'A2B2');
	})

	it('should be able to replace B1 with B2', function() {
		sinon.stub(DummyModule, 'B', function() {
			return 'B2';
		})

		should.equal(DummyModule.A(), 'A1B2');
	})

	it('should be able to replace E1 with E2', function() {
		sinon.stub(DummyModule.C.prototype, 'E', function() {
			return 'E2';
		});
		var c = new DummyModule.C();

		should.equal(c.D(), 'D1E2');
	})

	it('should be able to replace G1 with G2', function() {
		sinon.stub(DummyModule.F, 'G', function() {
			return 'G2'+DummyModule.F.H();
		})

		should.equal(DummyModule.F.G(), 'G2H1');
	});


});