Unit testing of private functions with Mocha and Node.js

Question

I am using Mocha in order to unit test an application written for Node.js.

I wonder if it's possible to unit test functions that have not been exported in a module.

Example:

I have a lot of functions defined like this in foobar.js:

function private_foobar1(){
    ...
}

function private_foobar2(){
    ...
}

And a few functions exported as public:

exports.public_foobar3 = function(){
    ...
}

The test case is structured as follows:

describe("private_foobar1", function() {
    it("should do stuff", function(done) {
        var stuff = foobar.private_foobar1(filter);
        should(stuff).be.ok;
        should(stuff).....

Obviously this does not work, since private_foobar1 is not exported.

What is the correct way to unit-test private methods? Does Mocha have some built-in methods for doing that?

Answer 1

Check out the rewire module. It allows you to get (and manipulate) private variables and functions within a module.

So in your case the usage would be something like:

var rewire = require('rewire'),
    foobar = rewire('./foobar'); // Bring your module in with rewire

describe("private_foobar1", function() {

    // Use the special '__get__' accessor to get your private function.
    var private_foobar1 = foobar.__get__('private_foobar1');

    it("should do stuff", function(done) {
        var stuff = private_foobar1(filter);
        should(stuff).be.ok;
        should(stuff).....