Jest to Vitest Migrator

Jest uses jest.config.js/ts with a top-level object, while Vitest uses vitest.config.ts wrapping settings inside a test: {} block via defineConfig(). Vitest also reuses your existing vite.config.ts, so many settings like path aliases transfer automatically. The biggest change is swapping preset/transform settings for Vitest's native ESM and TypeScript support.

For most projects, minimal changes are needed. Vitest is Jest-compatible — describe, it, test, expect, beforeEach, afterAll all work identically. The main differences are: (1) import { vi } from 'vitest' instead of using jest global, (2) vi.fn() instead of jest.fn(), (3) vi.mock() instead of jest.mock(). If you enable globals: true in vitest.config.ts, you don't even need to import these.

Replace jest.mock('module') with vi.mock('module'). The factory function syntax is identical. For manual mocks in __mocks__/ directory, Vitest supports the same pattern. For module-specific mocks, use vi.mock('module', () => ({ default: vi.fn() })). The key difference: use vi.spyOn() instead of jest.spyOn(), and vi.resetAllMocks() instead of jest.resetAllMocks().

Vitest handles TypeScript and JSX natively via Vite — no need for ts-jest, babel-jest, or @babel/preset-env. Remove these from your config entirely. If you used @swc/jest for speed, Vitest already uses esbuild by default (even faster). The only transform you might need is for CSS or static assets (handled the same way as in vite.config.ts).

Jest's moduleNameMapper becomes resolve.alias in vitest.config.ts (or vite.config.ts). Convert { '^@/(.*)$': '<rootDir>/src/$1' } to { '@': path.resolve(__dirname, './src') } in the resolve.alias block. This is identical to Vite path aliases — if you already have vite.config.ts with aliases, Vitest inherits them automatically.

Explicit imports (import { describe, expect, vi } from 'vitest') are the recommended approach for new projects — they're more explicit and TypeScript-friendly without extra tsconfig setup. However, if you're migrating a large codebase from Jest, enable globals: true temporarily to avoid touching every test file, then gradually migrate to explicit imports as you update each file.