Typing the Test Suite

Writing tests with Jest and TypeScript

Testing Nodejs and Express

Testing React with Testing Library

Writing custom matchers and mock modules

jаvascript and basic TypeScript knowledge

Basic React and Nodejs knowledge

What is this

A quick course for intermediate level developers looking to get started with testing using Jest and TypeScript.

The first section focuses on using Jest with jаvascript and a bit of TDD. The rest of the course uses TypeScript, Jest, with either Node.js or React. It's 2 hours long and full of content.

We move fast, break things, then write tests to make sure they don't break again. The technologies used are:

Jest (v26)

TypeScript (v4)

React.js (v17)

React Testing Library (v11)

Who is this for

Developers with some jаvascript/TypeScript, Node.js and React experience who'd like to learn to write tests.

Highly motivated bner who likes to jump in the deep end.

Required knowledge

I assume students have basic jаvascript knowledge.

The Node.js section assumes basic Node.js/Express knowledge, and the React section assumes some React knowledge. The testing concepts are largely unrelated to those specific frameworks, so as long as you have some programming experience, you should be fine.

Curriculum

1.0 Introduction

Get everything setup and starting writing some tests with Jest.

1.1 Installation

1.2 Your First Test

1.3 Adding an Assertion

1.4 Describing and Grouping Tests

1.5 Feedback Loop with Watch Mode

1.6 It.each for Concise Tests

2.0 Project: String Calculator

Put the skills learned in section one into practice by completing the String Calculator Kata.

2.1 The First Test

2.2 Handling Whitespace

2.3 Throwing an Error

2.4 Testing the Error

2.5 Validating the Test Suite with a Functional Refactor

2.6 Completing the Functional Refactor

3.0 Matcher Madness

Do a deep dive into the various matchers Jest provides, from toBe and toEqual to the more exotic resolves and rejects matchers.

3.1 toBe

3.2 toEqual, not

3.3 toHaveProperty

3.4 Resolves matcher for Promises

3.5 Rejects matcher for Errors

3.6 toHaveBeenCalled and Mock Functions

3.7 Waiting with the Done Callback

4.0 TypeScript, Node.js and Jest

We introduce TypeScript and Jest by developing and testing a Node.js API. Note: This section assumes basic knowledge of Node.js and Express.

4.1 TypeScript and Jest with ts-jest

4.2 Express Setup

4.3 The Jest Lifecylce: Before and After Hooks

4.4 Better Types

4.5 Adding JWT and a Refactor

4.6 Authorization Header

4.7 Testing for Success

4.8 Testing for Failure

4.9 Alternative Failed Assertion Syntax

4.10 Summary

5.0 TypeScript, React and Testing in a DOM Environment

Build a toy React app and see how to use TypeScript and Jest for DOM based testing with Testing Library. Note: this section assumes basisc knowledge of React.

5.1 Create React App and TypeScript

5.2 Rendering with Testing Library

5.3 Testing Library Assertions - getByText

5.4 useState and Asynchronous Assertions

5.5 Fetchign Data with useEffect

5.6 More Async Behavior with findAll

5.7 Mocking Axios with Jest Mocks

5.8 Toggling Todos

6.0 Jest Tips and Tricks

Learn some of Jest's more advanced features. Write your own custom matchers with TypeScript and write more robust, reuseable and (mostly) type-safe mocks.

6.1 Section Overview

6.2 Custom Matcher API

6.3 Implementing the Matcher

6.4 Typing the Matcher

6.5 Setting up for Module Mocking

6.6 Inline Mocks Review

6.7 The Problem with Inline Mocks

6.8 Manual Mocks

6.9 Default Module Data

6.10 Typing the Mock Module

6.11 Improving the Spec Types

6.12 Jest Spies

6.13 What Next More Learning Resources

Intermediate developers looking to brush up on testing




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