Independence

Module dependency injection for easy and fast mocking.

Enables a module to quickly create clones of itself that have their dependencies mocked.

When writing the module

Wrap your module in "require('independence')(require, module, (function(require, module, exports) {" + yourCode + "}))".

// monkey.js

require('independence')(require, module, function(require, module, exports){

  var moment = require('moment');
  var _ = require('lodash');
  var myService = require('../common/lib/services/myService');
  var myDatabase = require('../common/lib/myDatabase');

  exports.fling = function() {
    console.log('fling', moment().format 'YYYY-MM-DD');
  };

  exports.swing = function() {
    console.log('swing', _.find([1, 2, 3, 5, 7], (n) -> n % 2 is 0));
  };
});

With CoffeeScript, you can require() the provided coffee-wrap to automatically wrap all your .coffee modules when transpiling them to JavaScript.

When using the module

This works as normal:

// someModule.js

var monkey = require('./monkey');

monkey.fling(); // Will output `fling 2014-05-23`
monkey.swing(); // Will output `swing 2`

When testing the module

// tests/monkey.js

var monkey = require('./monkey');

function momentMock() {
  return {
    format: function() {
      return "Yaaap!";
    }
  };
}


// Provide only moment and leave all other dependencies undefined:
var pureMonkey = monkey.independence('isolate', {moment: momentMock});

pureMonkey.fling() // Outputs `fling Yaaap!`
pureMonkey.swing() // Fails because `_` is an empty Object


// Override moment, but leave all other dependencies nominal:
var testMonkey = monkey.independence('override', {moment: momentMock});

testMonkey.fling() // Outputs `fling Yaaap!`
testMonkey.swing() // Works as normal


// Override moment in the monkey module and in ALL its wrapped dependencies
// recursively (in this case, myService and myDatabase):
var testMonkey = monkey.independence('rebuild', {moment: momentMock});

But what if two modules have the same name?

// controller.js
var userModel = require('../lib/models/user');
var userController = require('./user');

...

// tests/controller.js
var controller = require('../controllers/controller');

var testController = controller.independence('isolate', {
    'models/user': userModelMock,
    'controllers/user': userControllerMock
  });

...

Other stuff you can do

Chain dependency objects:

var commonDependencies = {
  lodash: require('lodash'),
  myDatabase: {log: function(){}},
  myService: function(){ return 'serviced';}
};

var testMonkey = monkey.independence('isolate', commonDependencies, {
  moment: function(){ return {format: function(){ return 'Yip!';}};}
};

Clone & monkey-patch:

var database = require('database');

var databaseTest = database.independence('override');
databaseTest.getBananas = function(callback) {
  callback(null, ['banana1', 'banana2']);
};

Coffee & Mocha

If you're using CoffeeScript and Mocha you can use bin/coffee-wrap to compiles and wraps .coffee modules with the Independence header:

mocha --compilers coffee:independence/bin/coffee-wrap