Vitest Config

vitest.config.ts is the configuration file for Vitest, the Vite-native test framework. It uses defineConfig from 'vitest/config' and lets you set the test environment, coverage options, global helpers, and setup files. If your project already has a vite.config.ts, Vitest can extend it — so you often only need a separate vitest.config.ts when you want test-specific settings that differ from your build config.

node (default) is fastest and suits pure logic, utilities, and API code. jsdom simulates a browser DOM inside Node.js and is required for testing React/Vue components with @testing-library. happy-dom is a faster but less complete DOM implementation — good for component tests when speed matters more than 100% browser fidelity.

With globals: true, Vitest injects describe, it, test, expect, beforeEach, afterEach, etc. as global variables. You don't need to import them in each test file — this matches the Jest default behavior. Without globals, you write: import { describe, it, expect } from 'vitest'. The explicit import style is recommended for new projects because it's more explicit and plays better with editors and type-checking.

v8 uses Node.js's built-in V8 engine coverage — zero instrumentation overhead, install with npm install -D @vitest/coverage-v8. istanbul instruments your source code by injecting counters at every branch — it's slower but more precise for complex conditional logic, install with npm install -D @vitest/coverage-istanbul. For most projects v8 is the right choice; switch to istanbul if you need accurate branch-level reporting.

Add a thresholds block inside coverage: { thresholds: { lines: 80, branches: 70, functions: 80, statements: 80 } }. Vitest will exit with a non-zero code if any threshold is not met, failing your CI pipeline. For the full configuration, use the Vitest Config Generator tool which includes threshold sliders.