Learn Chai, Flux and Mocha

Chai is a BDD / TDD assertion library for node and the browser that can be delightfully paired with any javascript testing framework.

chai

[Chai](https://npmjs.com/package/chai) assertions work great with the [Mocha](https://npmjs.com/package/mocha) testing framework. In this lesson we'll walk through out to install Chai and [karma-chai](https://npmjs.com/package/karma-chai) so you can use the `expect` assertions in your tests.

Use Chai assertions for tests in a Karma project

React is one of the web’s most popular frameworks for building JavaScript applications. 

If you know what you’re doing, React can drastically simplify how you build, use, and maintain code.

Whether you’re a React newbie or you’re ready for advanced techniques, you can level-up with egghead. Explore our in-depth courses, lessons, and community resources to build more powerful applications and crack open your career.

react

Actions contain no functionality, but rather describe an event in our application.  In this lesson we will describe our Actions as they relate to our application.  These Actions will then be available for triggering in our Views and for execution in our Store.

React Flux: Actions

In Flux our Components are referred to as Views, but they are the same familiar Components associated with any React development.  In Flux, however, we have the benefit of the architecture to keep us from having to pass down through a long chain of children Components any functionality that may be embedded in our Stores.  In this Lesson we will wire up all of our Components in record time utilizing the architecture we've already established.

React Flux: Components/Views

Stores are where the real work in our application is done.  Dispatchers broadcast Actions to all Stores, and the Stores registered to listen for those Actions will perform any logic needed to update our Views.  In this lesson we will establish our first Store and register the Actions we wish to respond to.

React Flux: Stores

Our build process during this series will utilize both gulp and browserify.  In this lesson we will take a moment to setup our environment and all of the tooling required to begin developing our Flux Application.  We've kept the build process very simple so porting it to grunt should be a breeze, but this also serves as a simple primer for those who may not be familiar with gulp.

React Flux: Development Environment Setup

Organizing modules and components is a critical aspect of the development of any single-page web application (SPA). In this lesson we will look at refactoring the Flux React store into a more module structure.

React Flux: Project Organization

Flux has four major components: Stores, Dispatchers, Views, and Actions.  These components interact less like a typical MVC and more like an Event Bus.  In this lesson we will start by creating our Dispatcher which queues up our Actions as Promises and executes them as they are received.  We'll also create an AppDispatcher which, unlike the Dispatcher, is more specific to our application.

React Flux: Overview and Dispatchers

As your React Flux application grows, it is inevitable that you start to see functionality and code repeated. With React, you can easily keep things DRY by using mixins.

React Flux: Remove Duplicate Code with Mixins

With this lesson, we will bring it all together, using what we've learned in the series to fisnish out the React Flux architecture example.

The completed code for this series can be found [here on Github](https://github.com/eggheadio/egghead-react-flux-example).

React Flux: Wrapping Up

By default, React doesn't have built in routing. We will add routing to our application with the react-routing-component.

React Flux: Routing with react-router-component

Mocha is a feature-rich JavaScript test framework running on Node.js and in the browser, making asynchronous testing simple and fun. Mocha tests run serially, allowing for flexible and accurate reporting, while mapping uncaught exceptions to the correct test cases.

mocha

Every dependable library needs to have tests to ensure that you don't push accidental bugs. In this lesson, see how you can set up mocha and chai to start testing your library.

Setting up Unit Testing with Mocha and Chai

Now that you've got everything set up with mocha and chai, it's time to actually write tests. In this lesson you'll learn how to use `describe` and `it` to outline your tests and make sure you don't break your library in the future.

Unit Testing with Mocha and Chai

Mocha is a testing framework that provides structure for unit tests. In this lesson, we will be setting up Mocha with npm and npm scripts, writing a "Hello World" unit test, then writing the code to make the test pass (as an example of Test Driven Development (TDD), with the "red-green-refactor" workflow).

JavaScript Testing Fundamentals: Hello world unit test with Mocha (in ES6)

In this lesson, we will use Chai's request method to test our Node application's API responses.
By the end of this lesson, you will know how to:
- install the prerequisites to use mocha and chai in your application
- test for HTTP status response codes
- test for a string of text on a page
- test for a json response and validate the properties of the object
- write tests that not only verify the response of your application, but the behavior as well


Test Node RESTful API with Mocha and Chai

Writing great ES6 style Promises for Node.js is only half the battle. Your great modules must include tests as well to ensure future iterations don't break them. In this lesson, I show you a simple ES6 Promise in Node.js, then walk you through creating tests in Mocha using chai and chai-as-promised to test both resolve and reject methods.

Testing ES6 Promises in Node.js using Mocha and Chai

In this lesson, you will learn how to verify your API server is returning HTTP 400 responses when clients submit incorrect data. Returning HTTP 400 ensures that your clients are notified of the incorrect usage. Testing for them ensures your API returns errors instead of incorrect responses when supplied with incorrect data.

Test for HTTP 400 responses with Mocha and Chai

Unit testing functions that invoke callbacks can require a lot of setup code. Using `sinon.spy` to create a fake callback function can simplify your unit tests while still allowing you to observe the output of the function you're testing.

Unit Test a Function that Invokes a Callback with a Sinon Spy

When testing functions that make HTTP requests, it's not preferable for those requests to actually run. Using the `nock` JavaScript library, we can mock out HTTP requests so that they don't actually happen, control the responses from those requests, and assert when requests are made.

Mock an HTTP request using Nock while unit testing

When mocking a JavaScript function during a unit test, it can be helpful to force a mock function to return a value of your choosing. This allows you to verify that functions you're testing will behave correctly for every possible use case.

Much like [`sinon.spy()`](https://sinonjs.org/releases/v7.0.0/spies/), [`sinon.stub()`](https://sinonjs.org/releases/v7.0.0/stubs/) creates a mock function that prevents a real function from running. But, unlike `spy`, it also allows you to declare what value you'd like the mock function to return.

Mock a function's return value using a Sinon stub

Node.js is a platform built on Chrome's JavaScript runtime for easily building fast, scalable network applications. Node.js uses an event-driven, non-blocking I/O model that makes it lightweight and efficient, perfect for data-intensive real-time applications that run across distributed devices.

node

Sometimes when writing a unit test, you know that the module you're testing imports a module that you would like to observe, or at the very least mock to prevent side effects like network activity or file system operations.

For JavaScript unit tests that run in Node, we can hijack the built-in `require` function by using the [`proxyquire`](https://www.npmjs.com/package/proxyquire) module, which allows us to mock one or more modules that are second-class dependencies in our unit test, replacing them with whatever we want.

This means we could replace functions with [no-ops](https://en.wikipedia.org/wiki/NOP_%28code%29) to prevent side effects, or replace them with [Sinon spies](https://egghead.io/lessons/mocha-unit-test-a-function-that-invokes-a-callback-with-a-sinon-spy) to observe the inner workings of the module you're testing.

In this video, we'll demonstrate the basics of using Proxyquire to prevent and observe a file system operation.

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