Hamberfim / Typescript-Jest-Template

A template for using Typescript and Jest

Typescript-Jest Template

A template for using Typescript and Jest

The usual setup steps

Create a src folder for the source code and a test folder for the unit tests

1. mkdir src
2. mkdir tests

Use npm to initiate a new project at the root directory

3. npm init -y

Add TypeScript as a development dependency

4. npm i typescript --save-dev

Generate a tsconfig.json and modify it's setting

5. tsc --init
6. changes the setting in tsconfig.json to your prefs.

Add Jest as a development dependency

7. npm install jest --save-dev

Install the ts-jest package that contains a preprocessor with source map between TypeScript and Jest

8. npm install ts-jest --save-dev

Install the type definitions for Jest

9. npm install @types/jest --save-dev

Create the entry point file that will be transpiled to js.

10. Create an index.ts file in the 'src' directory where you will place your code - in our test a function called add() which also must be exported as a module i.e.,

export function add(a: number, b: number): number {
  // return sum of two numbers
  return a + b;
}

OR

function sum(a, b) {
  return a + b;
}
module.exports = sum;

Create a matching test file.

11. Create a file inside tests named index.test.ts

Import the code you will test

12. We import the add function from the index.ts file to out jest test file. Then, we write a new test suite that describes the function and inside that, we creates the first test based on our tests/rules i.e.,

const sum = require('./index');

test('adds 1 + 2 to equal 3', () => {
  expect(sum(1, 2)).toBe(3);
});

OR

import { add } from "../src/index";
describe("test add function in index file", () => {
  test("Adding two numbers", () => {
    expect(add(2, 1)).toBe(3);
  });
});

Create jest config file | or use jest --init

13. Create a “jest.config.js” at the root of the project that contains:

module.exports = {
  transform: {'^.+\\.ts?$': 'ts-jest'},
  testEnvironment: 'node',
  testRegex: '/tests/.*\\.(test|spec)?\\.(ts|tsx)$',
  moduleFileExtensions: ['ts', 'tsx', 'js', 'jsx', 'json', 'node']
};

Set up your test to run

14. Add the following section to your package.json:

{
  "scripts": {
    "test": "jest --watchAll --verbose --coverage"
    }
}

Run tsc and Run tests in terminals

15. tsc --watch and npm test