---
description: Migrate from the unstable_dev API to writing tests with the Workers Vitest integration.
title: Migrate from unstable_dev
image: https://developers.cloudflare.com/og-docs.png
---

[Skip to content](#main-content)

> Documentation Index  
> Fetch the complete documentation index at: https://developers.cloudflare.com/workers/llms.txt  
> Use this file to discover all available pages before exploring further.

# Migrate from unstable\_dev

Last updated Aug 24, 2026|Copy as Markdown|[View as Markdown](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/workers/testing/vitest-integration/migration-guides/migrate-from-unstable-dev/index.md)|[Agent setup](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/agent-setup/)

Note

Cloudflare recommends using the [createTestHarness()](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/workers/testing/test-harness/) API, which provides a harness specifically designed for integration testing.

The [unstable\_dev](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/workers/wrangler/api/#unstable%5Fdev) API has been a recommended approach to run integration tests. The `@cloudflare/vitest-plugin` package integrates directly with Vitest for fast re-runs, supports both unit and integration tests, and provides 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](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/workers/testing/vitest-integration/write-your-first-test/).

## Reference a Worker for integration testing

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

```js
import { unstable_dev } from "wrangler"

it("dispatches fetch event", () => {
  const worker = await unstable_dev("src/index.ts");
  const resp = await worker.fetch("http://example.com");
  ...
})
```

With the Workers Vitest integration, you can accomplish the same goal using `exports` from `cloudflare:workers`. `exports.default` refers to the default export defined by the `main` option in your [Wrangler configuration file](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/workers/wrangler/configuration/). This `main` Worker runs in the same isolate as tests so any global mocks will apply to it too.

```js
import { exports } from "cloudflare:workers";
import "../src/"; // Currently required to automatically rerun tests when `main` changes

it("dispatches fetch event", async () => {
	const response = await exports.default.fetch("http://example.com");
	...
});
```

## 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 configuration file](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/workers/wrangler/configuration/) by adding it as an option:

```js
await unstable_dev("src/index.ts", {
	config: "wrangler.toml",
});
```

With the Workers Vitest integration, you can now set this reference to a [Wrangler configuration file](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/workers/wrangler/configuration/) in `vitest.config.js` for all of your tests:

```js
import { cloudflareTest } from "@cloudflare/vitest-plugin";
import { defineConfig } from "vitest/config";

export default defineConfig({
	plugins: [
		cloudflareTest({
			wrangler: {
				configPath: "wrangler.jsonc",
			},
		}),
	],
});
```

## 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](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/workers/reference/migrate-to-module-workers/) 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](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/workers/testing/vitest-integration/write-your-first-test/#define-types) to define types for all of your tests.

```diff
- import { unstable_dev } from "wrangler";
- import type { UnstableDevWorker } from "wrangler";
+ import worker from "src/index.ts";

  describe("Worker", () => {
-   let worker: UnstableDevWorker;
    ...
  });
```

## Related resources

* [Write your first test](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/workers/testing/vitest-integration/write-your-first-test/#define-types) \- Write unit tests against Workers.

Was this helpful?

YesNo

## On this page

[![](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/_astro/logo.te5VL_aD.svg)Docs](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/)

```json
{"@context":"https://schema.org","@type":"TechArticle","@id":"https://developers.cloudflare.com/workers/testing/vitest-integration/migration-guides/migrate-from-unstable-dev/#page","headline":"Migrate from unstable_dev · Cloudflare Workers docs","description":"Migrate from the unstable\\_dev API to writing tests with the Workers Vitest integration.","url":"https://developers.cloudflare.com/workers/testing/vitest-integration/migration-guides/migrate-from-unstable-dev/","inLanguage":"en","image":"https://developers.cloudflare.com/og-docs.png","dateModified":"2026-08-24","publisher":{"@type":"Organization","name":"Cloudflare","description":"One platform for your apps, agents, and workforce. Build, secure, and scale without managing infrastructure","url":"https://www.cloudflare.com/","sameAs":["https://github.com/cloudflare","https://www.linkedin.com/company/cloudflare","https://x.com/cloudflare"],"logo":{"@type":"ImageObject","url":"https://developers.cloudflare.com/logo.svg"},"address":{"@type":"PostalAddress","streetAddress":"101 Townsend St","addressLocality":"San Francisco","addressRegion":"CA","postalCode":"94107","addressCountry":"US"},"contactPoint":[{"@type":"ContactPoint","contactType":"Customer Support","url":"https://support.cloudflare.com/","availableLanguage":["English"]},{"@type":"ContactPoint","contactType":"Sales","url":"https://www.cloudflare.com/contact/","availableLanguage":["English"]}]},"isPartOf":{"@type":"WebSite","@id":"https://developers.cloudflare.com/#website","name":"Cloudflare Docs","url":"https://developers.cloudflare.com/"}}
```