dependency injection example for mocking with testing

.gitignore

node_modules/

_.js

module.exports = require('./')._;

get-test.js

var _ = require('./')._ = require('./underscoreMocked');
require('./').http = require('./httpMocked');

var get = require('./get');
var expect = require('expect.js');

describe('get', function() {

    it('should have called _.map', function(done) {
        get("http://example.com", function(err, data) {
            expect(data).to.eql([3, 6, 9]);
            expect(_.map.callCount).to.be(1);
            done();
        });
    });

});

get.js

var _ = require('./_');
var http = require('./http');

module.exports = function(url, callback) {
    http.get(url, function(res) {
        var data = '';
        res.on('data', function(chunk) { data += chunk; });
        res.on('end', function() {
            data = JSON.parse(data);
            // using the _ dependency here
            callback(null, _.map(data, function(thing) {
                return thing * 3;
            }));
        });
    });
};

http.js

module.exports = require('./').http;

httpMocked.js

var EventEmitter = require('events').EventEmitter;

exports.get = function(options, callback){

    var response = new EventEmitter();

    callback(response);

    response.emit('data', '[1,2,3]');
    response.emit('end');

};

index.js

exports.http = require('http');
exports._ = require('underscore');

package.json

{
  "name": "di",
  "version": "0.0.0",
  "description": "Dependency Injection Example",
  "main": "index.js",
  "repository": {
    "type": "git",
    "url": "https://gist.github.com/4966457.git"
  },
  "author": "Arian Stolwijk",
  "license": "MIT",
  "dependencies": {
    "mocha": "1.8",
    "expect.js": "0.2",
    "underscore": "1.4"
  }
}

underscoreMocked.js

function map(array, callback, context){
    map.callCount++;
    return array.map(callback, context);
}

map.callCount = 0;

exports.map = map;