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Migrate from unstable_dev

The unstable_dev API has been a recommended approach to run integration tests. The @cloudflare/vitest-pool-workers package integrates directly with Vitest for fast re-runs, supports both unit and integration tests, all whilst providing isolated per-test storage.

This guide demonstrates key differences between tests written with the unstable_dev API and the Workers Vitest integration. For more information on writing tests with the Workers Vitest integration, refer to Write your first test.

​​ Reference a Worker for integration testing

With unstable_dev, to trigger a fetch event, you would do this:

import { unstable_dev } from "wrangler"
it("dispatches fetch event", () => {
const worker = await unstable_dev("src/index.ts");
const resp = await worker.fetch("");

With the Workers Vitest integration, you can accomplish the same goal using SELF from cloudflare:test. SELF is a service binding to the default export defined by the main option in your wrangler.toml. This main Worker runs in the same isolate as tests so any global mocks will apply to it too.

import { SELF } from "cloudflare:test";
import "../src/"; // Currently required to automatically rerun tests when `main` changes
it("dispatches fetch event", async () => {
const response = await SELF.fetch("");

​​ Stop a Worker

With the Workers Vitest integration, there is no need to stop a Worker via worker.stop(). This functionality is handled automatically after tests run.

​​ Import Wrangler configuration

Via the unstable_dev API, you can reference a wrangler.toml configuration file by adding it as an option:

await unstable_dev("src/index.ts", {
config: "wrangler.toml",

With the Workers Vitest integration, you can now set this reference to wrangler.toml in vitest.config.js for all of your tests:

export default defineWorkersConfig({
test: {
poolOptions: {
workers: {
wrangler: {
configPath: "wrangler.toml",

​​ Test service Workers

Unlike the unstable_dev API, the Workers Vitest integration does not support testing Workers using the service worker format. You will need to first migrate to the ES modules format in order to use the Workers Vitest integration.

​​ Define types

You can remove UnstableDevWorker imports from your code. Instead, follow the Write your first test guide to define types for all of your tests.

- import { unstable_dev } from "wrangler";
- import type { UnstableDevWorker } from "wrangler";
+ import worker from "src/index.ts";
describe("Worker", () => {
- let worker: UnstableDevWorker;