How to access and test an internal (non-exports) function in a node.js module?

Question

I\'m trying to figure out on how to test internal (i.e. not exported) functions in nodejs (preferably with mocha or jasmine). And i have no idea!

Let say I have a mo

Answer 1

EDIT:

Loading a module using vm can cause unexpected behavior (e.g. the instanceof operator no longer works with objects that are created in such a module because the global prototypes are different from those used in module loaded normally with require). I no longer use the below technique and instead use the rewire module. It works wonderfully. Here's my original answer:

Elaborating on srosh's answer...

It feels a bit hacky, but I wrote a simple "test_utils.js" module that should allow you to do what you want without having conditional exports in your application modules:

var Script = require('vm').Script,
    fs     = require('fs'),
    path   = require('path'),
    mod    = require('module');

exports.expose = function(filePath) {
  filePath = path.resolve(__dirname, filePath);
  var src = fs.readFileSync(filePath, 'utf8');
  var context = {
    parent: module.parent, paths: module.paths, 
    console: console, exports: {}};
  context.module = context;
  context.require = function (file){
    return mod.prototype.require.call(context, file);};
  (new Script(src)).runInNewContext(context);
  return context;};

There are some more things that are included in a node module's gobal module object that might also need to go into the context object above, but this is the minimum set that I need for it to work.

Here's an example using mocha BDD:

var util   = require('./test_utils.js'),
    assert = require('assert');

var appModule = util.expose('/path/to/module/modName.js');

describe('appModule', function(){
  it('should test notExposed', function(){
    assert.equal(6, appModule.notExported(3));
  });
});