---
description: Write integration tests using Wrangler's `unstable_startWorker()` API
title: Wrangler's unstable_startWorker()
image: https://developers.cloudflare.com/og-docs.png
---

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# Wrangler's unstable\_startWorker()

Last updated Aug 25, 2026|Copy as Markdown|[View as Markdown](https://4f1c5cd2.previews.developers.cloudflare.com/workers/testing/unstable%5Fstartworker/index.md)|[Agent setup](https://4f1c5cd2.previews.developers.cloudflare.com/agent-setup/)

Caution

`unstable_startWorker()` is deprecated. Cloudflare recommends using the [createTestHarness()](https://4f1c5cd2.previews.developers.cloudflare.com/workers/testing/test-harness/) API, which provides a harness specifically designed for integration testing.

The [unstable\_startWorker()](https://4f1c5cd2.previews.developers.cloudflare.com/workers/wrangler/api/#unstable%5Fstartworker) API exposes the internals of the Wrangler dev server, and allows you to customize how it runs. Compared to using [Miniflare directly for testing](https://4f1c5cd2.previews.developers.cloudflare.com/workers/testing/miniflare/writing-tests/), you can pass in a Wrangler configuration file, and it will automatically load the configuration for you.

This example uses `node:test`, but should apply to any testing framework:

```ts
import assert from "node:assert";
import test, { after, before, describe } from "node:test";
import { unstable_startWorker } from "wrangler";

describe("worker", () => {
	let worker;

	before(async () => {
		worker = await unstable_startWorker({ config: "wrangler.json" });
	});

	test("hello world", async () => {
		assert.strictEqual(
			await (await worker.fetch("http://example.com")).text(),
			"Hello world",
		);
	});

	after(async () => {
		await worker.dispose();
	});
});
```

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