Mocking support

[mcollina]

I think it would be awesome if we had mocking support, similar to nock.

[adamovittorio]

@mcollina what can we do to help here, do you have an idea on how to do the magic? In my understanding undici is not using nodejs HTTP module under the hood, so we need to intercept the request in another way.

[mcollina]

Send a PR :). I would recommend to add a MockedClient and then some support for mocking inside Pool, or maybe a MockingPool, and the rest will follow.

[adamovittorio]

What do you mean by adding a MockedClient? Just implementing a mocked version of the undici client?

In my understanding, we want something that intercepts the undici network calls and returns a mocked response.

const { MockClient } = require("undici");
const client = new MockClient("https://www.nodejs.org");

client.intercept({
  path: "/",
  method: "GET",
}).reply(200, { "foo": "bar"});

Wherever in you code you use undici to perform a GET https://www.nodejs.org/ the result is { "foo": "bar" } 200.

Still, I don't know how to intercept the requests

[mcollina]

The API you are sketching is correct!

Still, I don't know how to intercept the requests

Neither would I! You might have to overload a few (or all) of the APIs in Client.

[piranna]

You might have to overload a few (or all) of the APIs in Client.

According to docs, it would be a matter of overwrite just only client.dispatch().

[jonnydgreen]

I'm very happy to work on an implementation based on @adamovittorio's suggestion if that's okay with everyone? If so, it'll include the MockClient definition, tests, docs and typings :)

[mcollina]

Go for it @jonnydgreen! Open a draft PR as early as possible so when can provide iterative feedback.

[jonnydgreen]

Awesome! Will do, I'll submit a draft PR for initial feedback as soon as possible! :)

[Nytelife26]

If I may add, would it not be better to put the mocking in a separate package? Many users will not be using the mock functionality, and it is not integral to undici's function, so perhaps it should be put in an undici-mocks (or similar) package?

In regards to undici not using HTTP under the hood, I believe intercepting the requests at the net level is the better option since that would mock all Node network operations - both simultaneously removing the need for Nock and other individualized wrappers for various libraries.

[piranna]

+1 to the independent package. Regarding mocking net built-in, it's interesting but too much low-level, we would not be able to intercept at HTTP layer... we would already need a module built on top of that net mock to do it.

[Nytelife26]

@piranna Gotcha, it was more of a concept inspired by the old net-interceptor package.

Thank you for the +1 though. It seems like the dev team are keen to get it released first and then look into separating the packages later on, so hopefully, this will be done soon.

[gr2m]

similar to nock

Hey Matteo, I'm helping maintain nock. Can you tell why requests with undici cannot be mocked with nock at this point? It works with all other request libraries, as far as I know?

[piranna]

Can you tell why requests with undici cannot be mocked with nock at this point? It works with all other request libraries, as far as I know?

AFAIK nock intercept requests at Node.js built-in http module, while undici is built from scratch directly on top of Node.js built-in net module, so nock doesn't have a clue about the requests done by undici.

[Nytelife26]

It works with all other request libraries, as far as I know?

That is exactly why. undici isn't a request library like others. It is intended to be an alternative to http, not a wrapper for it, and nock uses http, as @piranna correctly said earlier.

[ronag]

@mcollina can we close this?

[mcollina]

Yes it's done

[mrded]

Yes it's done

@mcollina, can you please share here a link, or an example of how to mock undici requests?

I'm sure many people will end up on this issue, and also wonder how to do that. Thanks.