Using rewire to deal with private methods in SUT

module.js

var m_otherMod

/**
 * Here is called db method of db that should be stubbed
 * @private
 * @param a
 * @param b
 * @return {*}
 */
function privateMethodThatShouldBeTested(a, b) {
    return m_otherMod.func(a, b)
}

/**
 * otherMod is used indirectly
 * @public
 * @param a
 * @param b
 * @return {*}
 */
var m_exportedFunction  = function(a, b) {
    return privateMethodThatShouldBeTested(a, b)
}


module.exports.init = function(otherMod) {
    m_otherMod = otherMod

    var self = {
        exportedFunction : m_exportedFunction
    }

    return self
}

module.spec.js

//  See: http://freetymekiyan.github.io/2014/07/02/rewire/
var sinon         = require('sinon'),
    chai          = require('chai'),
    sinonChai     = require('sinon-chai'),
    rewire        = require('rewire');

var should = chai.should()
chai.use(sinonChai)

describe('module.js', function () {
    var mod,
        sut,
        sandbox,
        otherMod,
        privateFunc,
        privateFuncStub

    beforeEach(function (done) {
        sandbox = sinon.sandbox.create()

        // Rewire the file to be tested.
        mod = rewire('../lib/module.js')

        // Now all private memebers can be accessed (read and write)

        // save private function from rewired module
        privateFunc = mod.__get__('privateMethodThatShouldBeTested')

        otherMod = {
            func: sandbox.stub()
        }

        sut = mod.init(otherMod)

        done()
    })

    it('can stub private method in SUT', function (done) {
        // Stub should return 4
        // Create stub
        privateFuncStub = sandbox.stub()

        // Override private methdos with stub
        mod.__set__('privateMethodThatShouldBeTested', privateFuncStub)

        privateFuncStub.returns(5)

        var result = sut.exportedFunction(2,2)

        should.exist(result)

        result.should.be.eql(5)

        privateFuncStub.should.have.been.called

        done()
    })

    it('can test private method', function (done) {
        // privateFunc = mod.__get__('privateMethodThatShouldBeTested')
        otherMod.func.returns(4)

        var sum = privateFunc(2,2)

        sum.should.be.eql(4)

        otherMod.func.should.have.been.calledWith(2,2)

        done()
    })

    afterEach(function (done) {
        // restore private method  manually
        mod.__set__('privateMethodThatShouldBeTested', privateFunc)

        sandbox.restore()

        done()
    })
})