Learn TypeScript 3 by Building Web Applications

Installing and configuring Jest

First of all, we need to install Jest and the necessary additions:

1. Install Jest using npm install jest --save-dev.
2. Install the typings for Jest using npm install @types/jest --save-dev.
3. Install the TypeScript preset for Jest using npm install ts-jest --save-dev.

We've used --save-dev because Jest will only be used during development.

We've installed ts-jest (https://kulshekhar.github.io/ts-jest), a preprocessor plugin for Jest that adds support for TypeScript and source maps.

4. Now, create a file called jest.config.js at the root of the project (that is, next to the package.json file), with the following contents:

module.exports = { roots: [ "<rootDir>/src" ], preset: 'ts-jest', testEnvironment: 'node', ...