package.json          → dependencies, scripts, type field
tsconfig.json         → paths, compiler options
wrangler.toml         → Cloudflare Workers project
vite.config.ts        → existing Vite setup (extend, don't replace)
vitest.config.ts      → already configured? just fill gaps
jest.config.*         → migration candidate
src/                  → source structure

# Base (always)
pnpm add -D vitest

# React projects — add jsdom and Testing Library
pnpm add -D @vitest/coverage-v8 jsdom @testing-library/react @testing-library/jest-dom @testing-library/user-event

# Workers projects — add Cloudflare test utilities
pnpm add -D @vitest/coverage-v8 @cloudflare/vitest-pool-workers

# Node/Hono projects
pnpm add -D @vitest/coverage-v8

# If migrating from Jest, also remove:
pnpm remove jest ts-jest @types/jest jest-environment-jsdom babel-jest

import { defineWorkersConfig } from "@cloudflare/vitest-pool-workers/config";

export default defineWorkersConfig({
  test: {
    globals: true,
    poolOptions: {
      workers: {
        wrangler: { configPath: "./wrangler.toml" },
      },
    },
  },
});

/// <reference types="vitest/config" />
import { defineConfig } from "vite";
import { cloudflare } from "@cloudflare/vite-plugin";

export default defineConfig({
  plugins: [cloudflare()],
  test: {
    globals: true,
  },
});

/// <reference types="vitest/config" />
import { defineConfig } from "vite";
import react from "@vitejs/plugin-react";

export default defineConfig({
  plugins: [react()],
  test: {
    globals: true,
    environment: "jsdom",
    setupFiles: ["./src/test/setup.ts"],
    css: true,
  },
});

import { defineConfig } from "vitest/config";

export default defineConfig({
  test: {
    globals: true,
    environment: "node",
  },
});

  test: {
    // ... existing config
    coverage: {
      provider: "v8",
      reporter: ["text", "html", "lcov"],
      exclude: [
        "node_modules/",
        "**/*.config.*",
        "**/*.d.ts",
        "**/test/**",
      ],
    },
  },

import "@testing-library/jest-dom/vitest";

{
  "compilerOptions": {
    "types": ["vitest/globals"]
  }
}

{
  "scripts": {
    "test": "vitest",
    "test:run": "vitest run",
    "test:coverage": "vitest run --coverage",
    "test:ui": "vitest --ui"
  }
}

import { describe, it, expect } from "vitest";
import { app } from "../index";

describe("GET /health", () => {
  it("returns 200 with status ok", async () => {
    const res = await app.request("/health");
    expect(res.status).toBe(200);

    const body = await res.json();
    expect(body).toEqual({ status: "ok" });
  });
});

import { describe, it, expect } from "vitest";
import { render, screen } from "@testing-library/react";
import userEvent from "@testing-library/user-event";
import { Button } from "./Button";

describe("Button", () => {
  it("renders with label", () => {
    render(<Button>Click me</Button>);
    expect(screen.getByRole("button", { name: /click me/i })).toBeInTheDocument();
  });

  it("calls onClick when clicked", async () => {
    const user = userEvent.setup();
    const handleClick = vi.fn();
    render(<Button onClick={handleClick}>Click me</Button>);

    await user.click(screen.getByRole("button"));
    expect(handleClick).toHaveBeenCalledOnce();
  });
});

import { describe, it, expect } from "vitest";
import { formatCurrency } from "./format";

describe("formatCurrency", () => {
  it("formats whole numbers", () => {
    expect(formatCurrency(1000)).toBe("$1,000.00");
  });

  it("formats decimals", () => {
    expect(formatCurrency(49.9)).toBe("$49.90");
  });

  it("handles zero", () => {
    expect(formatCurrency(0)).toBe("$0.00");
  });
});

pnpm test:run

import { vi, describe, it, expect } from "vitest";
import { getUser } from "./api";

vi.mock("./api", () => ({
  getUser: vi.fn(),
}));

it("mocks a module function", async () => {
  vi.mocked(getUser).mockResolvedValue({ id: 1, name: "Test" });
  const user = await getUser(1);
  expect(user.name).toBe("Test");
  expect(getUser).toHaveBeenCalledWith(1);
});

it("spies on console.warn", () => {
  const spy = vi.spyOn(console, "warn").mockImplementation(() => {});
  doSomethingThatWarns();
  expect(spy).toHaveBeenCalledOnce();
  spy.mockRestore();
});

import { vi, beforeEach, afterEach, it, expect } from "vitest";

beforeEach(() => {
  vi.useFakeTimers();
  vi.setSystemTime(new Date("2026-01-15T10:00:00Z"));
});

afterEach(() => {
  vi.useRealTimers();
});

it("uses controlled time", () => {
  expect(new Date().toISOString()).toBe("2026-01-15T10:00:00.000Z");
});

it("stubs fetch", async () => {
  const mockFetch = vi.fn().mockResolvedValue({
    ok: true,
    json: () => Promise.resolve({ data: "test" }),
  });
  vi.stubGlobal("fetch", mockFetch);

  const res = await fetch("/api/data");
  expect(mockFetch).toHaveBeenCalledWith("/api/data");

  vi.unstubAllGlobals();
});

it("matches snapshot", () => {
  const result = generateConfig({ debug: true });
  expect(result).toMatchSnapshot();
});

it("matches inline snapshot", () => {
  expect({ status: "ok", count: 3 }).toMatchInlineSnapshot(`
    {
      "count": 3,
      "status": "ok",
    }
  `);
});

describe.each([
  { input: "hello", expected: "HELLO" },
  { input: "world", expected: "WORLD" },
  { input: "", expected: "" },
])("toUpperCase($input)", ({ input, expected }) => {
  it(`returns ${expected}`, () => {
    expect(input.toUpperCase()).toBe(expected);
  });
});

// Before
import { jest } from "@jest/globals";
jest.mock("./api");
jest.fn();
jest.spyOn(obj, "method");

// After
import { vi } from "vitest";
vi.mock("./api");
vi.fn();
vi.spyOn(obj, "method");

pnpm remove jest ts-jest @types/jest jest-environment-jsdom babel-jest @jest/globals

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

export default defineWorkspace([
  "packages/*/vitest.config.ts",
]);