Learn Elixir, Jest and Reactfire

These videos include the introductory steps to writing your first Elixir function and beginning to understand some key concepts in Elixir that make it unique. 

Some of those concepts include:
- the Mix build tool
- project structure
- collections of functions written in modules
- function *arity*
- pattern matching and common uses for it
- the pipe operator

Elixir is a dynamic, functional language designed for building scalable and maintainable applications.

Elixir leverages the Erlang VM, known for running low-latency, distributed and fault-tolerant systems, while also being successfully used in web development and the embedded software domain.

elixir

Getting Started with Elixir

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

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

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

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

Bootstrap a new Elixir project using Mix (a build tool included when you install Elixir), with its built in project generation.

Additional resources:
- [Official introduction to Mix](https://elixir-lang.org/getting-started/mix-otp/introduction-to-mix.html#our-first-project)

Generate a new Elixir project using Mix

Elixir code is organized into groups of functions called modules. You can create your own modules and built on top of predefined modules that are a part of Elixir by default.

Additional resources: 
- [Getting started with Modules and function from Elixir docs](https://elixir-lang.org/getting-started/modules-and-functions.html)

Write a New Function Inside of an Elixir Module

The syntax to pass arguments into functions is akin to many other languages. Elixir functions are uniquely recognized when running based off of the number of arguments passed in (a term called *arity*). This means you can define functions with the same name, so long as a different number of arguments is passed in.

Arity is a key concept to be aware of when reading documentation and writing your own code.

Additional resources:
- [Information about arity](https://elixir-lang.org/getting-started/modules-and-functions.html#function-capturing)
- [Default arguments in functions](https://elixir-lang.org/getting-started/modules-and-functions.html#default-arguments)

Pass arguments into Elixir functions and understand arity

Elixir uses `=` as an operator, but rather than assigning values to variables with it, it *matches* values on the right hand side of the `=` with the left side. This can be used in simple values, more complex data structures, and powerful condition checking.

Put into simpler terms, pattern matching is Elixir's way of assigning variables.

Additional resources:
- [Elixir docs on pattern matching](https://elixir-lang.org/getting-started/pattern-matching.html)

Pattern match values in Elixir

Some common uses for pattern matching in Elixir include checking conditions and passing parameters into functions. It's useful for pulling out only specific variables from collections of data.

Additional resources:
- [Elixir docs on pattern matching](https://elixir-lang.org/getting-started/pattern-matching.html)

Pattern match in conditions and function parameters in Elixir

One of the strengths of [Nx](https://nx.dev) is that it provides you easy access to some of the best tooling available. As such, whenever you generate a new app or lib inside an Nx workspace, it automatically preconfigures Jest for you and even sets up some pre-generated tests.

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