The Importance of Unit Testing in Large-Scale Apps

## Why We Test Many junior developers see testing as a waste of time. "If the code works, why test it?" they ask. The answer is simple: **Code changes.** Six months from now, when you or a teammate changes a function, how do you know you didn't break something else? ### Types of Testing 1. **Unit Tests:** Testing a single function or component in isolation. 2. **Integration Tests:** Testing how different parts of your app work together. 3. **End-to-End (E2E) Tests:** Simulating a real user journey in the browser. ### Tools for the Modern Dev - **Vitest:** A fast, modern alternative to Jest, specially built for Vite projects. - **Playwright:** The best tool for E2E testing in 2026, replacing Selenium and Cypress. ### The TDD Workflow (Test-Driven Development) Write the test *before* you write the code. It sounds crazy, but it forces you to think about the requirements and edge cases first. ### Conclusion Testing isn't just about finding bugs; it's about giving yourself the confidence to deploy code on a Friday afternoon without fear.