Visual Testing
ResembleJS is an open-source JavaScript library for image analysis and comparison. It compares two images pixel by pixel, returns a similarity percentage, and generates a visual diff highlighting the differences. Unlike Percy or Applitools, ResembleJS is a library you integrate directly into your tests — no external service, no API
Real-Time Testing
Video calling features built on WebRTC SDKs like Daily.co and 100ms are notoriously difficult to test. The real-time nature, browser API dependencies, and multi-participant complexity create challenges that don't exist in typical web development. But skipping tests means discovering join failures, audio bugs, and token
Local-First
Replicache is the local-first sync framework that made optimistic UI updates on top of server-authoritative state mainstream. Its core bet: every mutation applies optimistically on the client, gets rebased when the server responds, and conflict resolution happens through a deterministic rebase algorithm. Testing this correctly requires understanding the
Cypress
Cypress custom commands let you extract repeated test logic into named, reusable commands that read like domain language: cy.login(), cy.createOrder(), cy.assertProductCard(). They live in cypress/support/commands.js, are available in all test files automatically, and accept parameters like regular functions. Well-designed custom commands reduce test
Contract Testing
Pact is a consumer-driven contract testing library that lets you define what a consumer (e.g., a frontend app or microservice) expects from a provider (e.g., an API), generate a contract file from those expectations, and verify the provider actually fulfills them — without spinning up both services at
Astro
Astro's hybrid rendering model is one of its most powerful features — you can mix static site generation (SSG) and server-side rendering (SSR) in the same project, choosing per page. A blog index might be static, a user dashboard SSR, and a product page somewhere in between with
Astro
Astro's island architecture is one of its defining features — you get static HTML for most of your page, with interactive components (islands) hydrated only where needed. This composable model is excellent for performance, but it introduces unique testing challenges: when does hydration happen? How do you test client:
Astro
End-to-end tests are where Astro's architecture really gets tested — navigation between pages, form submissions, SSR data loading, hydration of islands, and the subtle differences between your dev server and production build. Playwright is the right tool for this. It's fast, runs in real browsers,
Astro
Astro's component model is unique — .astro files are compiled at build time, which means standard component testing approaches from React or Vue don't apply directly. But with Vitest and Astro's experimental container API, you can write fast, reliable unit tests for your Astro components
Astro
Astro's API routes (files in src/pages/api/) let you build backend endpoints alongside your frontend pages. They handle HTTP methods, parse request bodies, set cookies, and return JSON — all within the same project. But they need their own testing approach: unit tests for handler logic, integration tests
Appium
WebdriverIO's Appium integration is the smoothest way to write mobile automation tests in JavaScript. The @wdio/appium-service handles starting and stopping Appium automatically, the configuration is declarative, and the same test code works against iOS and Android with minimal platform-specific branches. This guide covers setting up
Testing
Alpine.js components are deceptively simple to write and surprisingly tricky to test well. The library was designed for progressively enhancing server-rendered HTML — you sprinkle x-data, x-show, and x-on attributes into your markup, and Alpine wires up the reactivity. There's no build step, no