Unit Testing fetch calls in a Cloudflare Worker
Once you have a worker set up, you probably want to write tests for it. In this guide I will show how to write tests for outbound fetch() requests using vitest and miniflare. Originally I used the following guide to get the tests working but it seems not everything is included within the guide that may be obvious for first time Worker developers.
https://miniflare.dev/testing/vitest
Setup
Install Vitest
$ npm install -D vitest-environment-miniflare vitest
If you are not using service bindings you can use the following vitest.config.ts file:
import { defineConfig } from "vitest/config";
export default defineConfig({
test: {
environment: "miniflare",
},
})
Finally use the following to enable Typescript support and type checking
{
"compilerOptions": {
...
"types": [
"@cloudflare/workers-types",
"vitest-environment-miniflare/globals" // add this line
]
}
}
Minimum Worker Example
To be able to test a worker I had to use either a Service Worker format or have a handle() function that manipulated the request which was then called from the Module Worker. Here is an example worker
export default {
async fetch(
request: Request,
): Promise<Response> {
return await handleRequest(request)
},
};
async function handleRequest(request: Request): Promise<Response> {
const response = await fetch(request)
const newResponse = new Response(response.body, response);
newResponse.headers.set("x-new-header", "hello world")
return newResponse
}
This will simply makes a request to what was passed in, adds a new header and then returns the response.
Writing Tests
This can now be tested using the following
import { expect, it } from "vitest";
import { handleRequest } from ".";
const describe = setupMiniflareIsolatedStorage();
describe("Worker", () => {
