---
description: Use Wrangler's `createTestHarness()` API to test production build output from any Node.js test runner.
title: Run integration tests against your Worker's production build
image: https://developers.cloudflare.com/changelog/post/2026-07-21-integration-test-harness/og.png?v=65fbb30e80533702
---

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July 27, 2026

## Run integration tests against your Worker's production build

[Workers](https://developers.cloudflare.com/workers/)

Copy as Markdown| [View as Markdown](https://developers.cloudflare.com/changelog/post/2026-07-21-integration-test-harness/index.md)| [Agent setup](https://developers.cloudflare.com/agent-setup/)

Wrangler now provides `createTestHarness()`, an API for running integration tests against Workers built with [Wrangler or the Cloudflare Vite plugin](https://developers.cloudflare.com/workers/testing/test-harness/configure/#configure-worker-projects) from any Node.js test runner.

The test harness starts a local Worker server with [helpers for dispatching requests, resetting storage, and inspecting runtime logs](https://developers.cloudflare.com/workers/wrangler/api/#createtestharness).

This is useful for tests that need to:

- [Route requests across multiple Workers](https://developers.cloudflare.com/workers/testing/test-harness/interact-with-workers/#test-route-dispatch-across-workers)
- [Mock outbound `fetch()` requests](https://developers.cloudflare.com/workers/testing/test-harness/integrations/#mock-service-worker) with Node.js request mocking libraries such as [MSW ↗︎](https://mswjs.io/)
- [Run Playwright tests against a Worker](https://developers.cloudflare.com/workers/testing/test-harness/integrations/#playwright)

For example, this test starts two Workers and mocks an upstream API:

*tests/vitest.test.jsjs*

```js
import { afterAll, afterEach, beforeAll, test } from "vitest";
import { http, HttpResponse } from "msw";
import { setupServer } from "msw/node";
import { createTestHarness } from "wrangler";

const network = setupServer();
const server = createTestHarness({
	workers: [
		/** Includes `"routes": ["example.com/*"]` */
		{ configPath: "./workers/web/wrangler.jsonc" },
		/** Includes `"routes": ["api.example.com/v1/*"]` */
		{ configPath: "./workers/api/wrangler.jsonc" },
	],
});

beforeAll(async () => {
	network.listen({ onUnhandledRequest: "error" });
	await server.listen();
});

afterEach(async () => {
	network.resetHandlers();
	await server.reset();
});

afterAll(async () => {
	network.close();
	await server.close();
});

test("routes requests to each Worker", async ({ expect }) => {
	// Mock the outbound fetch used to load user profiles.
	network.use(
		http.get("http://identity.example.com/profile/123", ({ params }) => {
			return HttpResponse.json({ id: 123, name: "Ada" });
		}),
	);

	const apiWorkerResponse = await server.fetch(
		"http://api.example.com/v1/users/123",
	);
	expect(await apiWorkerResponse.json()).toEqual({
		id: 123,
		name: "Ada",
	});

	const webWorkerResponse = await server.fetch("http://example.com/users/123");
	expect(await webWorkerResponse.text()).toBe("Profile: Ada");
});
```

*tests/vitest.test.tsts*

```ts
import { afterAll, afterEach, beforeAll, test } from "vitest";
import { http, HttpResponse } from "msw";
import { setupServer } from "msw/node";
import { createTestHarness } from "wrangler";

const network = setupServer();
const server = createTestHarness({
	workers: [
		/** Includes `"routes": ["example.com/*"]` */
		{ configPath: "./workers/web/wrangler.jsonc" },
		/** Includes `"routes": ["api.example.com/v1/*"]` */
		{ configPath: "./workers/api/wrangler.jsonc" },
	],
});

beforeAll(async () => {
	network.listen({ onUnhandledRequest: "error" });
	await server.listen();
});

afterEach(async () => {
	network.resetHandlers();
	await server.reset();
});

afterAll(async () => {
	network.close();
	await server.close();
});

test("routes requests to each Worker", async ({ expect }) => {
	// Mock the outbound fetch used to load user profiles.
	network.use(
		http.get("http://identity.example.com/profile/123", ({ params }) => {
			return HttpResponse.json({ id: 123, name: "Ada" });
		}),
	);

	const apiWorkerResponse = await server.fetch(
		"http://api.example.com/v1/users/123",
	);
	expect(await apiWorkerResponse.json()).toEqual({
		id: 123,
		name: "Ada",
	});

	const webWorkerResponse = await server.fetch("http://example.com/users/123");
	expect(await webWorkerResponse.text()).toBe("Profile: Ada");
});
```

Cloudflare now recommends `createTestHarness()` for integration tests instead of [`unstable_startWorker()`](https://developers.cloudflare.com/workers/testing/unstable_startworker/) or [`unstable_dev()`](https://developers.cloudflare.com/workers/wrangler/api/#unstable_dev). To start a development server programmatically, use the Vite [`createServer()` ↗︎](https://vite.dev/guide/api-javascript.html#createserver) API with the [Cloudflare Vite plugin](https://developers.cloudflare.com/workers/vite-plugin/).

For more information about `createTestHarness()`, refer to the [Integration test harness guide](https://developers.cloudflare.com/workers/testing/test-harness/).

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