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Write your first test

This guide will instruct you through installing and setting up the @cloudflare/vitest-pool-workers package. This will help you get started writing tests against your Workers using Vitest. The @cloudflare/vitest-pool-workers package works by running code inside a Cloudflare Worker that Vitest would usually run inside a Node.js worker thread ↗. For examples of tests using @cloudflare/vitest-pool-workers, refer to Recipes.

Prerequisites

Install Vitest and @cloudflare/vitest-pool-workers

Open a terminal window and make sure you are in your project's root directory. Once you have confirmed that, run:

Terminal window
npm install vitest@2.1.8 --save-dev --save-exact
npm install @cloudflare/vitest-pool-workers --save-dev

The above commands will add the packages to your package.json file and install them as dev dependencies.

Define Vitest configuration

If you do not already have a vitest.config.js or vitest.config.ts file, you will need to create one and define the following configuration. You can reference a wrangler.toml file to leverage its main entry point, compatibility settings, and bindings.

import { defineWorkersConfig } from "@cloudflare/vitest-pool-workers/config";


export default defineWorkersConfig({
  test: {
    poolOptions: {
      workers: {
        wrangler: { configPath: "./wrangler.toml" },
      },
    },
  },
});

Add configuration options via Miniflare

Under the hood, the Workers Vitest integration uses Miniflare ↗, the same simulator that powers wrangler dev's local mode. Options can be passed directly to Miniflare for advanced configuration.

For example, to add bindings that will be used in tests, you can add miniflare to defineWorkersConfig:

export default defineWorkersConfig({
  test: {
    poolOptions: {
      workers: {
        main: "./src/index.ts",
        miniflare: {
          kvNamespaces: ["TEST_NAMESPACE"],
        },
      },
    },
  },
});

This configuration would add a KV namespace TEST_NAMESPACE that was only accessible in tests. Using this method, you can add or override existing bindings like Durable Objects or service bindings.

Define types

If you are using TypeScript, you will need to define types for Cloudflare Workers and cloudflare:test to make sure they are detected appropriately. Add a tsconfig.json in the same folder as your tests (that is, test) and add the following:

{
  "extends": "../tsconfig.json",
  "compilerOptions": {
    "moduleResolution": "bundler",
    "types": [
      "@cloudflare/workers-types/experimental",
      "@cloudflare/vitest-pool-workers"
    ]
  },
  "include": ["./**/*.ts", "../src/env.d.ts"]
}

Save this file, and you are ready to write your first test.

Write tests

If you created a basic Worker via the guide listed above, you should have the following fetch handler in the src folder:

export default {
  async fetch(request, env, ctx) {
    return new Response("Hello World!");
  },
};

This Worker receives a request, and returns a response of "Hello World!". In order to test this, create a test folder with the following test file:

import {
  env,
  createExecutionContext,
  waitOnExecutionContext,
} from "cloudflare:test";
import { describe, it, expect } from "vitest";
// Could import any other source file/function here
import worker from "../src";


describe("Hello World worker", () => {
  it("responds with Hello World!", async () => {
    const request = new Request("http://example.com");
    // Create an empty context to pass to `worker.fetch()`
    const ctx = createExecutionContext();
    const response = await worker.fetch(request, env, ctx);
    // Wait for all `Promise`s passed to `ctx.waitUntil()` to settle before running test assertions
    await waitOnExecutionContext(ctx);
    expect(await response.text()).toBe("Hello World!");
  });
});

Add functionality to handle a 404 path on the Worker. This functionality will return the text Not found as well as the status code 404.

export default {
  async fetch(request, env, ctx) {
    const { pathname } = new URL(request.url);


    if (pathname === "/404") {
      return new Response("Not found", { status: 404 });
    }


    return new Response("Hello World!");
  },
};

To test this, add the following to your test file:

it("responds with not found and proper status for /404", async () => {
  const request = new Request("http://example.com/404");
  // Create an empty context to pass to `worker.fetch()`
  const ctx = createExecutionContext();
  const response = await worker.fetch(request, env, ctx);
  // Wait for all `Promise`s passed to `ctx.waitUntil()` to settle before running test assertions
  await waitOnExecutionContext(ctx);
  expect(await response.status).toBe(404);
  expect(await response.text()).toBe("Not found");
});
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