Migrating To Vitest 4

This skill guides migration from Vitest 2.x/3.x to 4.x, focusing on breaking changes and deprecated patterns.

Migration Overview

Vitest 4.0 introduces breaking changes in:

1. Pool Architecture: Consolidated worker configuration
2. Coverage: Required explicit include patterns
3. Workspace: Replaced by projects array
4. Browser Mode: Separate provider packages
5. Dependencies: Moved to server namespace
6. Module Runner: New Vite-based implementation

Quick Migration Guide

Pool Configuration

Before (Vitest 3.x):

export default defineConfig({
  test: {
    maxThreads: 4,
    singleThread: true,
  },
});