Module 5: Testing Strategies

Testing is the confidence layer of your application. In this module, we move beyond “it works on my machine” to engineering rigorous, automated test suites that prevent regressions and enable fearless refactoring. We will cover the entire testing trophy: from unit tests with React Testing Library to full end-to-end user flows with Playwright.

1. Module Contents

  1. React Testing Library (RTL)
    • Core Concept: Testing behavior, not implementation details.
    • Focus: Unit and Integration testing for components.
    • Key Skills: Query priority (getByRole vs getByTestId), simulating user events, and testing custom hooks.
  2. E2E: Cypress & Playwright
    • Core Concept: Validating critical user journeys in a real browser.
    • Focus: System-wide reliability and cross-browser compatibility.
    • Key Skills: Auto-waiting, handling network flakiness, authentication setup, and visual regression.
  3. Mocking APIs
    • Core Concept: Isolating the frontend from backend instability.
    • Focus: Deterministic test environments.
    • Key Skills: Using Mock Service Worker (MSW) to intercept network requests, simulating 500 errors, and testing latency.
  4. Review & Cheat Sheet
    • Summary: Rapid recall of testing utilities and best practices.
    • Tools: Flashcards and comparison tables.

[!IMPORTANT] Why Testing Matters: A test suite is an investment. It costs time upfront but pays dividends in debugging time saved and bugs prevented.

Let’s start by understanding how to test components the way users use them.