Get started (58)

Last updated Jul 27, 2026 This guide shows how to write a basic integration test for a Worker with createTestHarness(). The example uses Vitest as the test runner and exercises a Worker built with Wrangler.

Prerequisites

You need:

Create a test harness

Import createTestHarness() from wrangler. Point the test harness at your Worker configuration file.

test/index.test.jsjs

import { createTestHarness } from "wrangler";

const server = createTestHarness({
    workers: [{ configPath: "./wrangler.jsonc" }],
});

test/index.test.tsts

import { createTestHarness } from "wrangler";

const server = createTestHarness({
    workers: [{ configPath: "./wrangler.jsonc" }],
});

Manage the test harness lifecycle

For simplicity, we will reuse a single server for the test suite and reset it after each test. You can also start a new server for each test if the tests do not share the same configuration.

test/index.test.jsjs

import { afterAll, afterEach, beforeAll } from "vitest";

beforeAll(async () => {
    // Start the server before all tests
    await server.listen();
});

afterEach(async () => {
    // Recreates storage and restores the original Worker options after each test
    await server.reset();
});

afterAll(async () => {
    // Close the server after all tests
    await server.close();
});

test/index.test.tsts

import { afterAll, afterEach, beforeAll } from "vitest";

beforeAll(async () => {
    // Start the server before all tests
    await server.listen();
});

afterEach(async () => {
    // Recreates storage and restores the original Worker options after each test
    await server.reset();
});

afterAll(async () => {
    // Close the server after all tests
    await server.close();
});

Write your first test

Use the helpers provided by the test harness to interact with the Worker and assert its behavior. For example, you can call server.fetch() to send a request to the Worker and assert against its response.

test/index.test.jsjs

import { test } from "vitest";

test("responds", async ({ expect }) => {
    const response = await server.fetch("/");
    expect(await response.text()).toBe("Hello World");
});

test/index.test.tsts

import { test } from "vitest";

test("responds", async ({ expect }) => {
    const response = await server.fetch("/");
    expect(await response.text()).toBe("Hello World");
});

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description: Use createTestHarness with Mock Service Worker and Playwright. title: Integrations image: https://developers.cloudflare.com/workers/testing/test-harness/integrations/og.png?v=d180095af1637ae1

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