`proxyquire` - error: cannot find module

Question

For some reason proxquire cannot find my module index.js. I must be doing something really stupid or obvious and can't see it.

Error:

  invoicer
    good request
      1) "before all" hook


  0 passing (9ms)
  1 failing

  1) invoicer good request "before all" hook:
     Error: Cannot find module '../index.js'
      at Function.Module._resolveFilename (module.js:338:15)
      at Proxyquire._disableModuleCache (/Users/mario/projects/_invoice/print-invoice/node_modules/proxyquire/lib/proxyquire.js:218:19)
      at Proxyquire._disableCache (/Users/mario/projects/_invoice/print-invoice/node_modules/proxyquire/lib/proxyquire.js:203:15)
      at Proxyquire._withoutCache (/Users/mario/projects/_invoice/print-invoice/node_modules/proxyquire/lib/proxyquire.js:173:27)
      at Proxyquire.load (/Users/mario/projects/_invoice/print-invoice/node_modules/proxyquire/lib/proxyquire.js:135:15)
      at getTestedModule (/Users/mario/projects/_invoice/print-invoice/test/test.js:89:12)
      at Context.<anonymous> (/Users/mario/projects/_invoice/print-invoice/test/test.js:69:28)
      at Hook.Runnable.run (/usr/local/lib/node_modules/mocha/lib/runnable.js:218:15)
      at next (/usr/local/lib/node_modules/mocha/lib/runner.js:259:10)
      at Object._onImmediate (/usr/local/lib/node_modules/mocha/lib/runner.js:276:5)
      at processImmediate [as _immediateCallback] (timers.js:345:15)

The strange thing is that I've got the same set-up for the tests on another app and it has no trouble finding the module there. I've even maintained the same version of proxyquire, changing it to the latest version still didn't fix it. index.js exists in the directory for the specified path.

This is my test code:

var chai = require('chai');
var sinonChai = require("sinon-chai");
var sinon = require('sinon');
chai.use(sinonChai);
var nock = require('nock');
var mockfs = require('mock-fs');

var proxyquire = require('proxyquire');

describe('invoicer', function () {

    var expect = chai.expect;

    var ResponseOptions = {
        "username": "Peter Pan",
        "user_address_line_1": "Never Never Land",
        "user_address_line_2": "Tree-house 99",
        "user_post_code": "E4 9BY",
        "delivery_address_line_1": "Hooks Boat",
        "delivery_address_line_2": "Dock 69",
        "delivery_post_code": "SE2 4C",
        "order_number": "234234234",
        "order_date": "20/12/2090",
        "dispatch_date": "20/12/2090",
        "items": [
            {
                "product_name": "Fairy Dust",
                "brand": "Airy fairy",
                "quantity": 5,
                "total": 2000
            }
        ],
        "grand_total": 2000,
        "user_email": "peter@flyaway.com"
    }

    beforeEach(function () {

        var api = nock("http://wherever.com")
            .get("/to/fake/order/55432")
            .reply(200, ResponseOptions);

    });

    describe("good request", function () {

        var createTransport, sendMail, url, testedModule, contextDoneSpy, request;

        before(function (done) {

            createTransport = sinon.spy();
            sendMail = sinon.spy();
            url = "http://wherever.com/to/fake/order/55432";
            constextDoneSpy = sinon.spy();
            mockfs({
                "../email.html": "<span><%= username %></span>"
            });
            request = sinon.spy();

            testedModule = getTestedModule(createTransport, sendMail, request);
            testedModule.Invoicer(url, { done: function () {
                contextDoneSpy.apply(null, arguments);
                done();
            }});
        });

        afterEach(function () {
            mockfs.restore();
        });

        it("context done was called", function () {

            expect(contextDoneSpy).to.have.been.called;
        });
    });

});

function getTestedModule (createTransport, sendMail, request) {
    return proxyquire('../index.js', {
        "nodemailer": function () {
            return {
                createTransport: createTransport,
                sendMail: sendMail
            }
        },
        'request': request
    });
}