Vitest Workspaces: Multi-Project Monorepo Test Execution Isolation

In large monorepos (Turborepo, Nx, pnpm workspaces), different packages often require distinct test environments. For example, @repo/ui needs happy-dom, while @repo/backend needs node with a real database instance.

Vitest Workspaces allows configuring multiple projects inside a single runner process using a vitest.workspace.ts file.

// vitest.workspace.ts
import { defineWorkspace } from 'vitest/config';

export default defineWorkspace([
  'packages/*',
  {
    test: {
      name: 'unit-backend',
      root: './services/api',
      environment: 'node',
      include: ['src/**/*.spec.ts'],
    },
  },
  {
    test: {
      name: 'frontend-components',
      root: './apps/web',
      environment: 'happy-dom',
      include: ['src/**/*.test.tsx'],
    },
  },
]);

Running vitest from the monorepo root automatically executes all projects in parallel while isolating their environment configs.