Jest Fundamentals

Master Jest configuration, test structure, assertions, and lifecycle hooks for JavaScript and TypeScript projects.

Jest Configuration

Create jest.config.js or jest.config.ts at project root:

// jest.config.js
module.exports = {
  preset: 'ts-jest',                    // Use ts-jest for TypeScript
  testEnvironment: 'node',              // 'node' for backend, 'jsdom' for frontend
  roots: ['<rootDir>/src'],
  testMatch: [
    '**/__tests__/**/*.ts',
    '**/?(*.)+(spec|test).ts'
  ],
  collectCoverageFrom: [