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 module like that:

function exported(i) {
   return notExported(i) + 1;
}

function notExported(i) {
   return i*2;
}

exports.exported = exported;

And the following test (mocha):

var assert = require('assert'),
    test = require('../modules/core/test');

describe('test', function(){

  describe('#exported(i)', function(){
    it('should return (i*2)+1 for any given i', function(){
      assert.equal(3, test.exported(1));
      assert.equal(5, test.exported(2));
    });
  });
});

Is there any way to unit test the notExported function without actually exporting it since it's not meant to be exposed?

Answer 1

The rewire module is definitely the answer.

Here's my code for accessing an unexported function and testing it using Mocha.

application.js:

function logMongoError(){
  console.error('MongoDB Connection Error. Please make sure that MongoDB is running.');
}

test.js:

var rewire = require('rewire');
var chai = require('chai');
var should = chai.should();


var app = rewire('../application/application.js');


var logError = app.__get__('logMongoError'); 

describe('Application module', function() {

  it('should output the correct error', function(done) {
      logError().should.equal('MongoDB Connection Error. Please make sure that MongoDB is running.');
      done();
  });
});