Learn Jest, Npm and Xstream

You can’t be everywhere at once. Neither can node packages. But with a utility called npx — included in npm v5.2 and later — you can interact and run with node modules even if they’re not downloaded locally. The same is true for gists and remote branches of GitHub. As long as npm installed, your work can be wherever you are.

This course from Elijah Manor unlocks the power of the npx utility. Over 17 minutes, we will examine the npx package runner and look through various scenarios where the tool is helpful when running node packages from the command line. You’ll learn to use npm to:

- test out various versions of a package
- run packages without globally installing
- run code directly from GitHub
- make working with packages much easier

npm is the package manager for JavaScript. Find, share, and reuse packages of code from hundreds of thousands of developers — and assemble them in powerful new ways.

Execute npm Package Binaries with the npx Package Runner

In this collection, we build a minimal flashcard application using React, primarily focusing on function components and the hooks API. To make sure we can understand and maintain existing code, there are also a few lessons toward the end that use class components so you can get familiar with the syntax. We cover important React concepts, and sprinkle in libraries that are pretty standard in the ecosystem like @reach/router, Jest, and React testing library. We start with create-react-app so we can get right into it without worrying about configuring tooling. There's [a separate course for that here](https://egghead.io/courses/modern-javascript-tooling-with-react?af=5mx0ie)

jest

Build a React App with the Hooks API

In this course we are going to work through properly setting up Enzyme with Jest to test rendered components. This includes the nitty gritty of making our testing environment work with various versions of React. After we get our environment setup ready, we’ll work through the different ways we can render a component within our test pages. With a rendered component we can now test component methods and properties to assert that they are what is intended. 

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

Test React Components with Enzyme and Jest

End-to-end testing assures you of a few things: that all the integrated pieces of an application properly function, all those pieces work together as expected, and your tests include and simulate real-user scenarios — something unit and integration tests just don't do.

This course introduces you to two great tools for E2E testing: 

* Puppeteer opens and runs applications in a Chromium browser and performs the actions it's given.
* Jest asserts that the integrated pieces work as expected and that add-on libraries like Faker and pixelmatch take our tests to the next level.

Over 9 lessons, we will create common application features and use Puppeteer and Jest to run different types of tests against them. You'll get practice using these tools to render content, mimic user activity, automate tests, and measure the overall performance of your application.

End to End Testing with Google's Puppeteer and Jest

npm is like a giant library of code building blocks. There are tons of these “blocks”, aka “packages” that we can compose together to build cool things. We can use packages by other developers, but we can also write and publish our own. 

In this course we will learn how to create, publish, and update our own packages. We will create a JavaScript utility module to filter out sensitive words from a string, including tests and development file watching. We will then cover publishing and updating our package. This same approach can be used to create and publish other types of packages too like components (React, Angular, Web Components etc.) and command line interfaces.

Publish JavaScript packages on npm

In this course we will introduce the topic of using npm scripts as a build tool. We will start simple and then continue to build a small website as we introduce new topics. By the end of the course, you'll know how to get started and what tools and techniques are needed for you to create your own set of build scripts.

How to Use npm Scripts as Your Build Tool

Here are all the Egghead.io lessons about testing with Jest! http://facebook.github.io/jest (https://kcd.im/egghead-jest)

Testing JavaScript with Jest

Kent walks us through the internals of dom-testing-library and react-testing-library. 

There is a lot of set-up and tear down when testing UI components. These two libraries take away a lot of the work required to test React components well. 

Jest is commonly used in tandem with react-testing-library to assert results of your components. Jest simulates most browser apis with jsdom. react-testing-library helps you get values out of your components the same way your end users will. 

Links from the show:
- [Testing Library](https://testing-library.com)
- [Testing Javascript](https://testingjavascript.com)
- [Unit vs Integration vs E2E](https://kentcdodds.com/blog/unit-vs-integration-vs-e2e-tests)
- [Why you shouldn't ReactDOM.render to the body](https://medium.com/@dan_abramov/two-weird-tricks-that-fix-react-7cf9bbdef375)
- [Effective Snapshot Testing]( https://kentcdodds.com/blog/effective-snapshot-testing/)
- [Dev Tips with Kent](https://youtu.be/ttmvAm6esSc)
- https://kcd.im/news

Understanding how react-testing-library works with Kent C. Dodds

The ability to pull in just about anything your project needs from npm is amazing, but it can also lead to bundle bloat if you aren't selective about what libraries you pull into your library. In this lesson, we'll take a look at bundlephobia.com, a tool that provides insights about a library's size. With bundlephobia, you can make informed decisions about what libraries you pull into your project and avoid unnecessary bundle bloat.

https://bundlephobia.com/

Make informed decisions about 3rd party npm libraries with bundlephobia

JavaScript® (often shortened to JS) is a lightweight, interpreted, object-oriented language with first-class functions, most known as the scripting language for Web pages, but used in many non-browser environments as well such as node.js or Apache CouchDB. It is a prototype-based, multi-paradigm scripting language that is dynamic, and supports object-oriented, imperative, and functional programming styles.

javascript

To be useful and trustworthy, your CLIs should be extraordinarily reliable. Investing in testing early will reap rewards in future. We show how to set up basic tests with Jest and Oclif's test helpers.

Test Node.js CLIs with Jest and Oclif

Components do more than just render an initial view based on props. Components may also maintain their own internal state and update that state in response to events. Those state changes, will then lead to updates to the rendered output. In this lesson, we'll cover how to test a component and verify that it behaves as expected when we simulate a click event.

Test Component Interactions with Jest and Testing Library

As the core unit of functionality in a React application, our components should be tested. Using Jest and Testing Library, we can render our individual components right in a test context and make assertions about their rendered output and behavior. Tests are a great way to work through API decisions, provide living documentation for your code, and to allow for confidence when refactoring. In this lesson, we'll create an initial test to verify the initial rendered output for a component, given specific props.

Test Component Rendering with Jest and Testing Library

Our unit tests should never rely on code that is outside our control and they certainly shouldn't be calling across the network to a server. A good test needs to be repeatable and fast and relying on outside systems and/or data doesn't help us meet those goals. In this lesson, we'll use mocks to create an environment where we control the response for service calls. This will allow us to be confident in our assertions and ensure our tests aren't flaky.

Mock Modules in a React Component Test

With Node.js installed, bootstrapping a react app is as simple as executing `create-react-app` with `npx`. No further downloads necessary.

Bootstrap a react app using create-react-app

Any time your test interacts with a React component in a way that results in a state update, you need to make sure you wrap that interaction in an `act` function call, otherwise you'll get the "not wrapped in act(...)" warning.

In this lesson you'll learn how you can use `act` with `@testing-library/react-hooks` to avoid potential bugs in your custom React hooks.

This is based on my blog post: [Fix the "not wrapped in act(...)" warning](https://kentcdodds.com/blog/fix-the-not-wrapped-in-act-warning)

Fix the "not wrapped in act(...)" warning when testing Custom Hooks

The dreaded `act(...)` warning is really annoying, but actually really important. I've yet to see it be wrong (even when I thought it must be!). Every time it's pointing out something that is important that I'm missing in my test. In this lesson we'll identify a missing piece to our test and use act to make sure we avoid that in the future.

This is based on my blog post: [Fix the "not wrapped in act(...)" warning](https://kentcdodds.com/blog/fix-the-not-wrapped-in-act-warning)

Fix the "not wrapped in act(...)" warning

There aren't many places you need to manually use `act` if you're using [React Testing Library's async utilities](https://testing-library.com/docs/dom-testing-library/api-async), but if you're using fake timers, you need to manually use `act` to avoid missing bugs in your code.

In this lesson you'll learn how to identify the cause of `act` warnings and how to resolve them.

This is based on my blog post: [Fix the "not wrapped in act(...)" warning](https://kentcdodds.com/blog/fix-the-not-wrapped-in-act-warning)

Fix the "not wrapped in act(...)" warning with Jest fake timers

Use cases for `useImperativeHandle` are few and far between, but if you're testing a component that uses this React hook, you need to wrap any function you expose which results in state updates when called in React's `act` utility. Otherwise you could be missing important things in your tests that could result in bugs shipped to production.

In this lesson we'll learn how to identify what needs to be wrapped in `act(...)` and how to wrap those interactions.

This is based on my blog post: [Fix the "not wrapped in act(...)" warning](https://kentcdodds.com/blog/fix-the-not-wrapped-in-act-warning)

Fix the "not wrapped in act(...)" warning when testing the useImperativeHandle Hook

If you're not careful you can write a test that's worse than having not tests at all. In this lesson we'll learn why that is and how you can avoid it by making sure your test can fail.

This is based on my blog post: [Make Your Test Fail](https://kentcdodds.com/blog/make-your-test-fail)

Make Your Test Fail

Leaflet is the leading open-source JavaScript library for mobile-friendly interactive maps. Weighing just about 38 KB of JS, it has all the mapping features most developers ever need.

leaflet

While there are a few options for building maps, [Leaflet](https://leafletjs.com/) is the most popular. Lucky for us, Leaflet is also available as a ReactJS component library with [React Leaflet](https://react-leaflet.js.org/). We'll use both Leaflet and React Leaflet to build a map in our React app.

To get started, we need to install:

[Leaflet (npmjs.com)](https://www.npmjs.com/package/leaflet) and [React Leaflet (npmjs.com)](https://www.npmjs.com/package/react-leaflet)

**[Click here for exercise instructions](https://github.com/colbyfayock/launchtime-workshop/tree/master/lessons/02%20-%20Adding%20Your%20First%20React%20Leaflet%20Map%20to%20a%20New%20React%20Application#1-installing-our-dependencies)**


Install Leaflet and react-leaflet with NPM in a JavaScript Project

Nx has been design to work especially well in large monorepos. One particularity (compare to other monorepo solutions) is that Nx follows the principle of having one single version of a package in the entire workspace. That said, you'll have one version of React, one version of Angular etc.. This helps to keep things consistent, facilitates code sharing as well as easier migrations.
In this lesson we're looking into adding the [material-ui](https://material-ui.com/) package to our React app.

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