MCP
Your MCP tool works in Claude Desktop. You've called it manually a dozen times. It returns results. You're confident. Then a user sends an unexpected input format, or calls two tools in sequence with shared state, or the downstream API your tool depends on returns a
MCP
Unit tests for MCP tool handlers are necessary but not sufficient. They test the function — they don't test whether the server correctly handles the MCP protocol, whether tools are advertised correctly, whether resources are listed as expected, or whether the transport layer survives malformed messages. Integration tests do.
MCP
Most MCP server tutorials skip authentication. The examples use stdio transport with no auth, the server runs locally, and there's nothing to secure. But if you're building an MCP server that exposes real capabilities — file access, database queries, API calls — and if that server is accessible
Test Automation
Vitest's browser mode runs your tests inside a real browser instead of a simulated DOM environment like jsdom or happy-dom. This matters because jsdom does not execute real JavaScript rendering, does not run CSS layout, and does not implement browser APIs like ResizeObserver, IntersectionObserver, or Web Components. When
Test Automation
Vite plugins extend the build pipeline with custom transforms, virtual modules, and build hooks. Testing them is harder than testing application code because a plugin's behavior is entangled with Vite's internals — module graphs, HMR events, rollup hooks. This guide covers a practical, reproducible approach to testing
Test Automation
H3 is the HTTP framework that powers Nitro, which in turn powers Nuxt 3's server engine. If you write server/api/*.ts or server/routes/*.ts files in a Nuxt project, you are writing H3 event handlers. Testing these handlers in isolation — without starting a full Nuxt or
Test Automation
Cloudflare Workers run in V8 isolates, not Node.js. That difference means standard testing approaches break: node:fs, node:http, and most Node.js built-ins are unavailable. Miniflare solves this by implementing the Workers runtime APIs locally — KV, R2, D1, Durable Objects, Queues — so your tests run in an environment
Test Automation
Biome is a high-performance JavaScript and TypeScript toolchain that replaces ESLint, Prettier, and several other tools with a single binary. It is written in Rust, has near-zero configuration overhead, and runs lint checks 10–100× faster than the Node.js equivalents. This guide covers everything you need to integrate Biome
Test Automation
Valtio creates proxy state that you mutate directly. Its simplicity is also what makes testing it slightly unconventional — there's no dispatch, no reducers, and the proxy itself is mutable. The keys are using snapshot() for immutable assertions and subscribe() for testing reactive behaviour. Setup npm install valtio npm
Test Automation
MobX uses observable state, computed values, and reactions to build reactive systems. Testing MobX is straightforward because stores are plain classes with transparent state — no providers, no reducers, no dispatch. You call methods, read properties, and assert. Setup npm install mobx mobx-react-lite npm install -D jest @testing-library/react @testing-library/user-event
Test Automation
Legend State is a high-performance state library built on a signals-based observable system. It's designed to minimize re-renders and handle large datasets efficiently. Testing it requires understanding how to read and write observables in tests, how to test computed values, and how to verify persistence. Setup npm install
Test Automation
Zustand is a small, fast state management library with a minimal API. Its stores are plain JavaScript objects with actions — which makes them straightforward to test. The main challenges are resetting state between tests, testing middleware like persist and immer, and testing stores integrated with React components. Setup npm install