Skip to content


Switch branches/tags

Name already in use

A tag already exists with the provided branch name. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. Are you sure you want to create this branch?
This branch is 31 commits ahead of 18F:18f-pages.

Latest commit


Git stats


Failed to load latest commit information.
Latest commit message
Commit time

Unit testing in Node.js

Build Status

This exercise will walk you through writing a small Node.js application and writing unit tests for it. You will learn how to:

  • structure your code to separate concerns effectively, which maximizes readability, maintainability, and testability
  • write small, focused tests for your application-specific logic
  • use a technique known as "dependency injection" to simulate interaction with a remote service
  • write an automated integration test for your application

This exercise assumes you are comfortable executing commands in a UNIX environment. Specifically, it expects that you are familiar with the basics of how to create directories and files on the command line of a terminal program.


Docker users: Ensure you have docker and docker-machine installed. Run ./ to build and run the docker image and open your web browser to appropriate web address. You may have to refresh after the server finally starts.

OS X users: Consider using Homebrew to install the software described below.

  1. Install Node.js on your system. This package requires version 4.2 or greater or version 5 or greater. You may wish to first install a version manager such as nvm to manage and install different Node.js versions.

  2. Install Ruby version 2.2.3 or greater on your system. You can see if it is already installed by running ruby -v in a terminal window. You may wish to first install a version manager such as rbenv to manage and install different Ruby versions.

    Why Ruby? The ./go script mentioned below is written in Ruby. The content is published and hosted locally using Jekyll, a Ruby application.

  3. Install git if you do not have it installed already.

  4. Clone this repository and change into the working directory by running:

    $ git clone
    $ cd unit-testing-node
  5. Run ./go serve to serve the site locally.

    The ./go script will check that your Ruby version is supported, install the Bundler gem if it is not yet installed, install all the gems needed by the exercise website, and launch a running instance on http://localhost:4000/.

  6. Visit http://localhost:4000/ in your browser.


Run all the installation instructions to make sure the site builds. Then, in your clone of this repository, run the following to ensure your installation is in a good state:

$ npm install
$ ./go ci_build

Directory structure

The directory layout is as follows (note that in this exercise, content in the directories other than pages pertains to the code used in the exercise):

  • pages: contains the content of the exercise website

  • exercise: contains the content that the person following the exercise will edit

  • .exercise-init: contains the content used to create the starting state of the exercise

    Note: The exercise and .exercise-init directories should always remain identical in the published version of the repo.

  • solutions: contains subdirectories containing solution content pertaining to chapters of the exercise

    • 00-CHAPTER: each chapter should have a corresponding directory containing the solution content for that chapter, with a unique numeric prefix reflecting the order of the chapters
    • complete: this directory should contain the solution content reflecting the completed exercise

Each 00-CHAPTER directory need not contain the full content from previous chapters; only the content that has changed relative to previous chapters. This is due to the way that the ./go commands to set exercise state work, discussed in the next section. However, each chapter should be self-contained and testable in isolation from other chapters.

The solutions chapter from this exercise contains:


./go commands to set exercise state

The ./go script will create the following Tutorial commands to set the state of the exercise directory:

  • start-over: sets the state to the very beginning of the exercise
  • set-CHAPTER: sets the state to that required at the beginning of CHAPTER, where CHAPTER corresponds to one of the OO-CHAPTER subdirectories within the solutions directory
  • set-complete: sets the state to that of the completed exercise

The Tutorial commmands from this exercise are:

Tutorial commands
  start-over         Restore the initial state of the exercise files
  set-config         Set up the files for the config chapter
  set-rule           Set up the files for the rule chapter
  set-slack-client   Set up the files for the slack-client chapter
  set-github-client  Set up the files for the github-client chapter
  set-log            Set up the files for the log chapter
  set-middleware     Set up the files for the middleware chapter
  set-integration    Set up the files for the integration chapter
  set-complete       Copy the complete solution into the exercise dir

Interaction between ./go and the directory structure

All of the ./go commands that update exercise state start by clearing out the exercise directory and copying over the files from .exercise-init.

Every set-CHAPTER command will then copy the files from each previous solutions/00-CHAPTER directory into exercise, one directory at a time. Since each 00-CHAPTER directory need only contain partial content, this process will build the complete state required at the beginning of the target exercise chapter.

(Note: This presumes that content files will not be removed during the course of the exercise; may want to revisit this mechanism in the future.)

The ./go set-complete command will reset the exercise state to the beginning before copying over all the files from solutions/complete.

gulpfile.js and npm command setup

All of the scripts in the package.json file are implemented via gulpfile.js:

  • The npm test and npm run lint commands only operate on the files in the exercise directory.
  • The npm run test-all command processes .exercise-init and all solutions subdirectories, in serial
  • npm run lint-all command processes every .js file in the project

Running a subset of tests

The buildArgs() function in gulpfile.js enables the following npm test syntax to allow running a subset of tests matching a regular expression:

$ npm test -- --grep '^Config '

Alternatively, if you want to use gulp directly:

$ npm install -g gulp
$ gulp test --grep '^Config '
$ gulp test-all --grep '^Config '

.eslintrc configuration

This project uses ESLint for static analysis. See the ESLint configuration user guide and ESLint rules guide for details on each parameter of the .eslintrc file.

Open Source License

This software is made available as Open Source software under the ISC License. For the text of the license, see the LICENSE file.

Prior work

This is derived from the original 18F/unit-testing-node implementation.


Introductory unit testing exercise in Node.js







No releases published


No packages published


  • JavaScript 96.8%
  • Ruby 2.3%
  • Other 0.9%