installation

Jest is installed just like any other dev dependancy.

npm install --save-dev jest

Or add it manually to your package.json if you are dockerized and rebuild your container.

TypeScript

📘 Jest Typescript Docs

TypeScript Packages

If you are using TypeScript you will also need to install some packages for Babel and TypeScript.

npm install --save-dev babel-jest @babel/core @babel/preset-env @babel/preset-typescript
npm install --save-dev ts-jest ts-node typescript

babel.config.js

and also add @babel/preset-typescript to the list of presets in your babel.config.js.

babel.config.js

module.exports = {
  presets: [
    ['@babel/preset-env', {targets: {node: 'current'}}],
    '@babel/preset-typescript',
  ],
};

.babelrc

create a .babelrc file in the root of your project and add the following:

.babelrc

{
  "presets": ["@babel/preset-env", "@babel/preset-typescript"]
}

jest.config.ts

create a jest.config.ts file in the root of your project and add the following:

jest.config.ts

import type {Config} from 'jest';

const config: Config = {
  preset: 'ts-jest',
  testEnvironment: 'node',
  transform: {
    '^.+\\.js$': 'babel-jest',
    '^.+\\.ts$': 'ts-jest',
  },
  moduleFileExtensions: ['ts', 'tsx', 'js', 'jsx'],
};

export default config;

tsconfig.json

You will need to add "jest" to the types array in your tsconfig.json file if you want your test files themselves to be in TypeScript.

tsconfig.json

{
  //...
  "types": [
    "jest"
    //...
  ]
  //...
}

note

Dear god the test files are so much more complicated when written in TypeScript... avoid like plague.

Creating Test Files

Jest will look for test files with the following naming conventions:

• Files with .js suffix in __tests__ folders.
• Files with .test.js suffix.
• Files with .spec.js suffix.

also if you have configured Jest to use TypeScript:

• Files with .ts suffix in __tests__ folders.
• Files with .test.ts suffix.
• Files with .spec.ts suffix.

Run Tests in Docker Container

📘 docs.docker.com > Node > Run Tests

First make sure that you have built your container with the new Jest and TypeScript dependancies.

Then you will run the following command to run the tests in the container, replacing NAME_OF_DOCKER_SERVICE with the name of the service in your docker-compose.yml file.

 docker compose run NAME_OF_DOCKER_SERVICE npm run test

For example if I have the following docker-compose.yml file:

docker-compose.yml

services:
 docusaurus:
   build:
     context: .
     dockerfile: dockerfile
   ports:
     - '3000:3000'
  ...

I would run the following command to run the tests in the container:

 docker compose run docusaurus npm run test

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