The [`unstable_dev`](https://developers.cloudflare.com/workers/wrangler/api/#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](https://developers.cloudflare.com/workers/testing/vitest-integration/get-started/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 `SELF` from `cloudflare:test`. `SELF` is a [service binding](https://developers.cloudflare.com/workers/runtime-apis/bindings/service-bindings/) to the default export defined by the `main` option in your [Wrangler configuration file](https://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 { 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("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://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://developers.cloudflare.com/workers/wrangler/configuration/) in `vitest.config.js` for all of your tests:

```js
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](https://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://developers.cloudflare.com/workers/testing/vitest-integration/get-started/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://developers.cloudflare.com/workers/testing/vitest-integration/get-started/write-your-first-test/#define-types) - Write unit tests against Workers.
