Cloudflare Developers•6mo ago

Mocking fetch with Jest for a Cloudlare Worker

Hi all - i'm trying to figure out something that potentially could be very simple. I've got a Worker running on Cloudflare that pulls data from an external API, via fetch. Inside my 'fetchData.ts' I have the following.

const response = await fetch(env.ENDPOINT, {
        method: "POST",
        headers: {
            Authorization: `Basic ${btoa(
                `someKey`
            )}]`,
            "Content-Type": "application/x-www-form-urlencoded"
        },
        body: "someBody"
    });

const response = await fetch(env.ENDPOINT, {
        method: "POST",
        headers: {
            Authorization: `Basic ${btoa(
                `someKey`
            )}]`,
            "Content-Type": "application/x-www-form-urlencoded"
        },
        body: "someBody"
    });

I'm trying to write a 'testData.test.ts' file to check that fetch was called with the correct args. If I was working with a node environment i'd just mock out node-fetch and check what the mock was called with. With the worker, fetch is global, so I have no idea what to mock. Any help with this would be much appreciated

2 Replies

MrBBot•6mo ago

Hey! 👋 You should be able to use jest.spyOn(globalThis, "fetch") to get a mock function. Can I also check how you're running your tests? Are you using jest-environment-miniflare, or something else?

jpbrown84•6mo ago

Thanks 🙂 I'm just using jest with "test": "npx jest", I've now got a version of this working using miniflare, thanks again

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Mocking fetch with Jest for a Cloudlare Worker