TypeScript

Jest · Reference cheat sheet

📋 Overview

Run TypeScript tests with ts-jest, @swc/jest, or Babel. Keep tsconfig and Jest transforms aligned for path aliases and JSX.

🔧 Core concepts

Prefer transpile-only for speed; run tsc --noEmit separately in CI.

💡 Examples

ts-jest preset:

npm i -D ts-jest typescript @types/jest
npx ts-jest config:init

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

SWC:

transform: {
  '^.+\\.(t|j)sx?$': ['@swc/jest', {
    jsc: { parser: { syntax: 'typescript', tsx: true } },
  }],
},

Globals import (ESM-friendly):

import { describe, expect, test } from '@jest/globals';

test('typed', () => {
  const n: number = 1;
  expect(n).toBe(1);
});

Path aliases: mirror paths from tsconfig in moduleNameMapper.

⚠️ Pitfalls

• Type errors only caught if ts-jest diagnostics enabled — don't assume.
• JSX runtime mismatches (react vs react-jsx).
• Mixing ESM ts-jest experimental mode without Node flags.
• Duplicate @types/jest vs Vitest types in the same project.
• Compiling tests into dist accidentally via broad include.

🔗 Related

• Install
• Config
• React Testing Library
• Module mocks
• Migration to Vitest
• Matchers