[jest] add type inference #32579

antoinebrault · 2019-01-29T02:13:29Z

Follow-up of #31094

Updated jest typings to use latest typescript features to infer mock types.

Breaking Change

With types inferred, mockImplementation(), mockReturnValue(), mock...() will not compile if they are not used with the right types.

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typescript-bot · 2019-01-29T02:22:33Z

@antoinebrault Thank you for submitting this PR!

🔔 @JoshuaKGoldberg @tkrotoff @cwoodland @johnny4753 @NoHomey @jwbay @asvetliakov @alexjoverm @epicallan @ikatyang @wsmd @JamieMason @douglasduteil @ahnpnl @JoshuaKGoldberg @UselessPickles @r3nya @Hotell @sebald @andys8 @dawnmist @geovanisouza92 @deadNightTiger @joscha @jonasheinrich @aldentaylor @bradleyayers - please review this PR in the next few days. Be sure to explicitly select Approve or Request Changes in the GitHub UI so I know what's going on.

If no reviewer appears after a week, a DefinitelyTyped maintainer will review the PR instead.

typescript-bot · 2019-02-03T02:25:25Z

A definition owner has approved this PR ⭐️. A maintainer will merge this PR shortly. If it shouldn't be merged yet, please leave a comment saying so and we'll wait. Thank you for your contribution to DefinitelyTyped!

jwbay · 2019-02-03T21:59:49Z

types/jest-in-case/jest-in-case-tests.ts

@@ -11,8 +11,8 @@ function subtract(minuend: number, subtrahend: number) {
 }

 beforeEach(() => {
-    jest.spyOn(global, 'describe').mockImplementation((title, fn) => fn());
-    jest.spyOn(global, 'test').mockImplementation((name, fn) => fn());
+    jest.spyOn(global, 'describe').mockImplementation((title, fn) => jest.fn());


Could you comment on the change here? Is this because fn is now correctly typed?

Don't know why I did that... I updated the PR.

fn should be cast to a function because it is unknown

jest.spyOn(global, 'describe').mockImplementation((title, fn) => (fn as () => void)());

jwbay · 2019-02-03T22:05:08Z

types/jest/index.d.ts

@@ -35,6 +36,8 @@ declare var xtest: jest.It;

 declare const expect: jest.Expect;

+type ArgsType<T> = T extends (...args: infer A) => any ? A : never;


TS ships with a Parameters type for this. Was it added after 3.0?

It was added in 3.1 (microsoft/TypeScript@60b4fe9)

Thanks for the info. I didn't even know about it since it's not in https://www.typescriptlang.org/docs/handbook/advanced-types.html

ERROR: 218:145 expect Compile error in typescript@3.0 but not in typescript@3.1. Fix with a comment '// TypeScript Version: 3.1' just under the header. Cannot find name 'Parameters'.

jwbay · 2019-02-03T22:17:26Z

types/jest/jest-tests.ts

+const spy6 = jest.spyOn(spiedTarget2, "value", "set");
+
+let spy7: jest.SpyInstance;
+spy7 = jest.spyOn(spiedTarget, "setValue");


What is this one trying to test since nothing is done with spy7?

just testing if spyOn can be assigned to default generics of jest.SpyInstance. spy4 is basically the same. I'll remove spy7 from the tests.

jwbay

Just a couple questions, but everything looks shippable to me. Love all the $ExpectTypes in the tests.

typescript-bot · 2019-02-05T01:10:19Z

I just published @types/expect-puppeteer@3.3 to npm.

typescript-bot · 2019-02-05T01:10:30Z

I just published @types/frisby@2.0 to npm.

typescript-bot · 2019-02-05T01:10:52Z

I just published @types/jest-axe@2.2 to npm.

typescript-bot · 2019-02-05T01:11:15Z

I just published @types/jest-in-case@1.0 to npm.

typescript-bot · 2019-02-05T01:11:26Z

I just published @types/jest-json-schema@1.2 to npm.

typescript-bot · 2019-02-05T01:11:44Z

I just published @types/jest-matchers@20.0 to npm.

typescript-bot · 2019-02-05T01:11:55Z

I just published @types/jest-plugin-context@2.9 to npm.

typescript-bot · 2019-02-05T01:12:10Z

I just published @types/jest-specific-snapshot@0.5 to npm.

typescript-bot · 2019-02-05T01:12:22Z

I just published @types/jest-when@1.1 to npm.

typescript-bot · 2019-02-05T01:12:37Z

I just published @types/storybook__addon-storyshots@3.4 to npm.

Jessidhia · 2019-02-05T01:16:48Z

The bot is becoming more clever 😮

Would be nice to just post a single time and edit the post as it progress, or only post once with the entire list:

I just published to NPM

<details><summary>9/9 packages</summary>

``\`
...
@types/jest-when@1.1
@types/storybook__addon-storyshots@3.4
``\`
</details>

I can see this being a problem should react ever bump minimum typescript version, for example...

armanio123 · 2019-02-05T01:21:31Z

Yeah, something we could definitely improve. I'll talk to the team about it and see what can be done.

Thanks for contributing.

Chris-V · 2019-02-05T17:35:16Z

This update is absolutely fantastic. I am having a couple issues with the implementation though.

When using Mocked<T, Y>, T[P] is mapped to the exact member type rather to (what I believe should be) the return type when it is a function.
The promise helpers (mockResolvedValue, ...) should unwrap the promise's argument type.

Here's a playground link to test it out: https://bit.ly/2WJN5F9 I also added some code below with a proper test syntax:

Test case
api.ts

interface Something {
    a: number;
}
class Api {
    async performAction(x: Something): Promise<Something> { /* do whatever */ }
}

api.spec.ts:

jest.mock('./api.ts');

import { Api } from './api';

describe('Demo', () => {
    let api: jest.Mocked<Api>;

    beforeEach(() => {
        api = new Api() as any;
    })

    it('should compile', () => {
        api.performAction.mockImplementation(() => Promise.resolve({ a: 1 }));
        api.performAction.mockReturnValue(Promise.resolve({ a: 2 }));
        api.performAction.mockResolvedValue({ a: 3 });
    });
});

Suggestion
So my suggestion is to extract the return type if T[P] is a function. I also suggest tweaking the promise helpers, otherwise they expect Promises as parameters which defies the intent.

type Mocked<T> = {
    [P in keyof T]: T[P] & MockInstance<T[P] extends (...args) => any ? ReturnType<T[P]> : T[P], ArgsType<T[P]>>;
} & T;

interface MockInstance<T, Y extends any[]> {
    mockResolvedValue(value: T extends PromiseLike<infer U> ? U : never): Mock<T, Y>;
    // same for resolvedOnce, reject, rejectOnce
}

antoinebrault · 2019-02-05T18:18:37Z

You're right. I'll look at it and add tests tonight.

I think it could be simplified:

type Mocked<T> = {
    [P in keyof T]: T[P] extends (...args) => any ? MockInstance<ReturnType<T[P]>, ArgsType<T[P]>>: T[P];
} & T;

I agree mockResolvedValue should unwrap. A better impl could be:

// considering this: await Promise.resolve(Promise.resolve(3)) === 3

mockResolvedValue(value: T extends PromiseLike<infer U> ? U | T : T | Promise<T>): Mock<T extends PromiseLike<any> ? T : Promise<T>, Y>;

https://bit.ly/2TyFXsW

SimenB · 2019-02-07T14:26:37Z

This is super awesome work - I had no idea TS would be able to infer as much as it's able to! 🎉

I'll be a bit sneaky and try to recruit help here.

We're currently migrating Jest itself to TypeScript (jestjs/jest#7807), and I'd love some help converting jest-mock. That's the underlying implementation behind jest.fn(), jest. genMockFromModule(), jest.spyOn et al..

superhawk610 · 2019-03-09T05:00:53Z

Looks like this broke ts-jest's mocked helper (see here). I'm working on upgrading the typings there to support these new inferences, any help would be 🔥

Antoine Brault and others added 10 commits December 5, 2018 10:09

[jest] add type inference

f8c68f6

Merge branch 'master' into jest-type-inference

5b6edfa

revert MockResult definition

3fdb22e

add mockImplementation optional arguments example

b337410

rollback default values

3236add

use any instead of {} for mock return type

fd07752

merge master

68242a4

add jest-when type inference

0ccaf36

Merge branch 'master' into jest-type-inference

d60a5cb

fn() should return type Mock<any, any>

3b921ef

antoinebrault mentioned this pull request Jan 29, 2019

[jest] add type inference #31094

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jwbay reviewed Feb 3, 2019

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typescript-bot added Owner Approved A listed owner of this package signed off on the pull request. Merge:Express and removed Awaiting reviewer feedback Unmerged The author did not merge the PR when it was ready. labels Feb 3, 2019

antoinebrault added 4 commits February 3, 2019 22:46

fn: unknown should be cast to a function

a0111a9

Merge branch 'master' into jest-type-inference

edd25d0

bump frisby jest version

50942f2

fix test

1ba138a

armanio123 merged commit 9bb7883 into DefinitelyTyped:master Feb 5, 2019

typescript-bot removed this from Check and Merge in Pull Request Status Board Feb 5, 2019

antoinebrault mentioned this pull request Feb 6, 2019

[jest] fix type inference for Mocked & mockResolvedValue/mockRejectedValue #32816

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orta mentioned this pull request Feb 7, 2019

feat(jest): bump to 24 kulshekhar/ts-jest#957

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orta mentioned this pull request Feb 8, 2019

spyOn(...).mockImplementation should return a SpyInstance rather than a Mock #17605

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SimenB mentioned this pull request Mar 4, 2019

[RFC] Migrate Jest to TypeScript jestjs/jest#7554

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[jest] add type inference #32579

[jest] add type inference #32579

antoinebrault commented Jan 29, 2019

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superhawk610 commented Mar 9, 2019

		@@ -35,6 +36,8 @@ declare var xtest: jest.It;

		declare const expect: jest.Expect;

		type ArgsType<T> = T extends (...args: infer A) => any ? A : never;

[jest] add type inference #32579

[jest] add type inference #32579

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antoinebrault commented Jan 29, 2019

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