RFC: Built-in support for HTTP mocking

[SimenB]

There's often a need to mock network calls when writing unit tests. While one can use jest.mock to implement the http API of your choice - or use modules like jest-fetch-mock that only works for fetch - this is often technical debt the moment you swap out your HTTP abstraction. If one migrates to request or axios, they often have to also switch out their mock implementation. This pain is potentially even worse if moving from e.g. traditional xhr requests to fetch, or vice versa. Or even starting to use GraphQL instead of the more traditional REST based approaches.

One could set up a mock server with some canned responses (e.g. create-test-server is nice), but that is often slower than you want it to be, especially for unit tests which needs to run against a clean instance every single test.

A third alternative, and what I want to see in Jest, is to mock out the http layer of the runtime. nock is a module which does this for node (so works fine also for JSDom based tests), but I find its API clunky to use and work with. Other alternatives are sinon or faux-jax.

If we could provide a simpler and/or more intuitive API out of the box with Jest, I think that might solve a lot of common issues where people today find solutions to plug into Jest.

I don't have any particular API suggestions here, but I think something akin to jest.useFakeTimers() (say jest.useFakeNetwork()) with related APIs such as jest.fakeGet('url', {headers}, body) might be a good start. Looking at existing solutions for inspirations sounds like a great way forward! Having something for GraphQL out of the box would be awesome as well.

One source of inspiration beyond sinon and faux-jax could be ava-nock. Especially the NOCK_MODE feature sounds like an awesome watch plugin for jest.

Done! 10 days isn't too bad :D

[ewolfe]

I'm interested in this. Right now I'm facing an issue where I want to assert that an HTTP request was made with a certain shape (host, path, search, body, etc), without caring about the response or even the return value from the containing function/method.

Do you think that use calls fall under this RFC?

[SimenB]

Yes, I'd say so 🙂 The functions would be jest spies essentially, so you would be able to do toHaveBeenCalledWith() and other goodies.

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@palmerj3 IIRC you said you had something at Spotify along these lines, any news on that?

[palmerj3]

@SimenB yeah we have this (something similar) at Spotify and our intention is to open source it this quarter. Happy to hop on video chat sometime and show you how it works.

[SimenB]

@palmerj3 awesome! Let's talk about it in Stockholm later this month :)

[ThisIsMissEm]

@palmerj3 @SimenB was there any follow-up to this?

[SimenB]

Yeah, @palmerj3 showed it to me, and it looked pretty good! 🙂 I don't know how the effort to open source it is going, though.

[dgreene1]

+1 Love to see what you're working on @SimenB

[codepunkt]

any news on this?

[palmerj3]

Not exactly what this issue is about but we did release this https://github.com/spotify/polly-jest-presets

[jeking3]

Doesn't https://github.com/ScaleLeap/jest-polly/ provide this?

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