The Complete Guide to Testing in JavaScript

Testing gives you confidence that your code works as expected. This guide covers unit tests, integration tests, and end-to-end tests for JavaScript applications.

Testing Pyramid

• Unit tests — fast, focused, many
• Integration tests — moderate, realistic
• E2E tests — slow, comprehensive, few

Tools

• Vitest / Jest for unit tests
• Playwright for E2E
• Testing Library for component tests

Write tests that give you confidence, not tests that give you coverage numbers.