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Teaches the agent to migrate a Jest suite to Vitest — vi.mock and the globals shim, vitest.config workspaces/projects, coverage, browser mode, and Vitest v4 breaking changes.
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SOC 職業分類に基づく
SKILL.md を表示中
| name | Vitest Migration & Config |
| description | Teaches the agent to migrate a Jest suite to Vitest — vi.mock and the globals shim, vitest.config workspaces/projects, coverage, browser mode, and Vitest v4 breaking changes. |
| version | 1.0.0 |
| author | thetestingacademy |
| license | MIT |
| tags | ["vitest","migration","jest","vi-mock","config","coverage","browser-mode","projects"] |
| testingTypes | ["unit","integration"] |
| frameworks | ["vitest","jest"] |
| languages | ["typescript"] |
| domains | ["web","api"] |
| agents | ["claude-code","cursor","github-copilot","windsurf","codex","aider","continue","cline","zed","bolt","gemini-cli","amp"] |
This skill makes the agent migrate a Jest test suite to Vitest correctly and configure Vitest from scratch. Vitest is mostly Jest-compatible, but the differences bite: the vi namespace replaces jest, vi.mock hoisting needs vi.hoisted, ESM is first-class, and Vitest v4 removed workspace files in favor of inline projects. The agent should produce a config that runs fast, types cleanly, and reports coverage.
Use this skill when migrating from Jest, setting up vitest.config.ts, splitting unit vs browser tests, or resolving v4 upgrade breakage.
vi replaces jest. jest.fn -> vi.fn, jest.mock -> vi.mock, jest.spyOn -> vi.spyOn, jest.useFakeTimers -> vi.useFakeTimers. The assertion API (expect, matchers) is unchanged.test.clearMocks/restoreMocks in config or call vi.clearAllMocks() in beforeEach — Vitest does not reset by default.vi.mock is hoisted; use vi.hoisted for shared values. Variables the factory needs must be created via vi.hoisted(() => ...), since the factory runs before imports.globals: true (Jest-like, no imports) or import { describe, it, expect, vi } from vitest. Pick one and add types: ['vitest/globals'] if using globals.projects, not workspace. The standalone vitest.workspace.ts file is removed; declare multiple environments via the inline projects array.browser.instances (v4) to run component tests in a real browser engine via Playwright.Most test bodies migrate with a namespace rename. With , even the imports can stay as-is.
globals: true// Before (Jest):
// const fn = jest.fn();
// jest.spyOn(obj, 'method');
// jest.useFakeTimers();
// After (Vitest) — explicit imports (recommended, ESM-safe):
import { describe, it, expect, vi, beforeEach } from 'vitest';
describe('cart', () => {
beforeEach(() => vi.clearAllMocks());
it('adds an item', () => {
const onChange = vi.fn();
const cart = createCart(onChange);
cart.add({ sku: 'A1', qty: 2 });
expect(cart.total).toBe(2);
expect(onChange).toHaveBeenCalledWith(expect.objectContaining({ sku: 'A1' }));
});
});
vi.mock with vi.hoisted (the hoisting fix)In Jest you prefix variables with mock. In Vitest, wrap them in vi.hoisted so they exist when the hoisted factory runs.
import { vi, test, expect, beforeEach } from 'vitest';
import { getUser } from './user-service';
import axios from 'axios';
// Create the spy in a hoisted block so the factory below can reference it.
const { mockGet } = vi.hoisted(() => ({ mockGet: vi.fn() }));
vi.mock('axios', () => ({
default: { get: mockGet }, // note: ESM default export shape
}));
beforeEach(() => vi.clearAllMocks());
test('resolves user from API', async () => {
mockGet.mockResolvedValue({ data: { id: 1, name: 'Ada' } });
const user = await getUser(1);
expect(user).toEqual({ id: 1, name: 'Ada' });
expect(axios.get).toHaveBeenCalledWith('/api/users/1');
});
importActualThe Vitest equivalent of jest.requireActual. The factory is async.
vi.mock('./config', async (importOriginal) => {
const actual = await importOriginal<typeof import('./config')>();
return {
...actual,
isProduction: vi.fn(() => false), // override one export, keep the rest real
};
});
vitest.config.tsCovers globals, environment, setup files, and coverage. This replaces jest.config.js.
import { defineConfig } from 'vitest/config';
export default defineConfig({
test: {
globals: true, // Jest-like; otherwise import from 'vitest'
environment: 'node', // 'jsdom' for component DOM tests
setupFiles: ['./test/setup.ts'],
clearMocks: true, // reset vi.fn() call data before each test
restoreMocks: true, // restore spies to original impl
coverage: {
provider: 'v8', // fast, no instrumentation step
reporter: ['text', 'html', 'lcov'],
include: ['src/**/*.ts'],
exclude: ['src/**/*.d.ts', 'src/**/index.ts'],
thresholds: { lines: 80, functions: 80, branches: 75 },
},
},
});
If using globals: true, add to tsconfig.json:
{ "compilerOptions": { "types": ["vitest/globals"] } }
projects (v4)The v4 replacement for vitest.workspace.ts. Run Node unit tests and jsdom component tests in one command, each with its own config.
import { defineConfig } from 'vitest/config';
export default defineConfig({
test: {
coverage: { provider: 'v8' },
projects: [
{
// Fast pure-logic tests in Node.
test: {
name: 'unit',
environment: 'node',
include: ['src/**/*.unit.test.ts'],
},
},
{
// DOM/component tests in jsdom.
test: {
name: 'dom',
environment: 'jsdom',
setupFiles: ['./test/dom-setup.ts'],
include: ['src/**/*.dom.test.ts'],
},
},
],
},
});
instances)For component tests that need a real browser. v4 replaced the singular browser.name with a browser.instances array.
import { defineConfig } from 'vitest/config';
export default defineConfig({
test: {
browser: {
enabled: true,
provider: 'playwright',
headless: true,
instances: [
{ browser: 'chromium' },
{ browser: 'firefox' },
],
},
},
});
// component.browser.test.ts — runs in a real browser
import { render } from 'vitest-browser-react';
import { expect, test } from 'vitest';
import { Counter } from './Counter';
test('increments in a real browser', async () => {
const screen = render(<Counter />);
await screen.getByRole('button', { name: 'Increment' }).click();
await expect.element(screen.getByText('Count: 1')).toBeVisible();
});
{
"scripts": {
"test": "vitest run",
"test:watch": "vitest",
"test:ui": "vitest --ui",
"coverage": "vitest run --coverage"
}
}
globals: true, add types: ['vitest/globals'] so TypeScript knows expect/vi.clearMocks and restoreMocks in config — Vitest does not auto-reset, so omitting them recreates Jest's "leaky mock" bug.vi.hoisted for any value a vi.mock factory references. This is the single most common migration failure.{ default: ... } in the factory — the shape differs from Jest's CJS interop.v8 coverage provider for speed; reserve istanbul only if you need its specific report nuances.project so the fast Node unit tests give quick feedback.vitest.workspace.ts with inline projects and convert browser.name to browser.instances.jest -> vi and assuming you're done. Mock hoisting and ESM default shapes still need vi.hoisted and { default }.vi.mock without vi.hoisted. It is undefined when the hoisted factory executes.vitest.workspace.ts on v4. It is removed; the suite silently ignores it or errors. Use projects.globals: true but not adding vitest/globals types, producing a flood of "cannot find name 'expect'" TS errors.node.@jest/globals imports into Vitest files — import from vitest instead.vitest.config.ts" / "configure Vitest coverage"vi.mock isn't working / variable is undefined in the factory"workspace / browser.name config"requireActual equivalent in Vitest"