[Bug]: jest.mocked function is not exported from jest object

[hudochenkov]

Version

27.4.3

Steps to reproduce

Try to use jest.mocked. E. g.:

// foo.ts
export const foo = { };

// foo.spec.ts
import {foo} from './foo';
jest.mock('./foo');

const mockedFoo = jest.mocked(foo);

Expected behavior

jest.mocked is defined and working.

Actual behavior

Error: TypeError: jest.mocked is not a function.

Also documentation is missing on https://jestjs.io/docs/jest-object, but present in source code: https://github.com/facebook/jest/blob/main/docs/JestObjectAPI.md#jestmockedtitem-t-deep--false

Additional context

jest.mocked was added in #12089, but seems it was not added to jest object, and only to jest-mock package.

Tagging author of original PR @k-rajat19

Environment

System:
    OS: macOS 11.6.1
    CPU: (8) x64 Intel(R) Core(TM) i5-1038NG7 CPU @ 2.00GHz
  Binaries:
    Node: 16.13.0 - /usr/local/bin/node
    Yarn: 1.22.17 - /usr/local/bin/yarn
    npm: 8.2.0 - /usr/local/bin/npm
  npmPackages:
    jest: ^27.4.3 => 27.4.3

[SimenB]

Ah, missed adding it to jest object. We need to add to https://github.com/facebook/jest/blob/c76f9a7c8eb2fab1a15dfe8952d125a8607d1bbe/packages/jest-environment/src/index.ts#L51 at which point we'll get a type error in jest-runtime which should lead the way

/cc @k-rajat19

[cduff]

Just updated to jest 27.4.4 which includes a fix for this issue but still can't use it as the function isn't in @types/jest? Do we have to wait for it to be added there or is there some other way we're supposed to get TS definitions for jest?

[k-rajat19]

Hi @cduff would be better if you share what exactly error you are getting while using mocked function because it is already added in jest object.

[SimenB]

@types/jest isn't maintained in this repo, so open up an issue (or PR) to https://github.com/DefinitelyTyped/DefinitelyTyped

[domdomegg]

Related discussion: DefinitelyTyped/DefinitelyTyped#57716

[cduff]

Hi @cduff would be better if you share what exactly error you are getting while using mocked function because it is already added in jest object.

Hi @k-rajat19, I run my jest tests using ts-jest and get jest types from @types/jest as suggested in the official jest documentation. I realise the mocked function has been added to the jest object but I can't use it as it doesn't exist according to @types/jest.

The DefinitelyTyped/DefinitelyTyped#57716 discussion will hopefully get this resolved.

One thing I don't understand though is how anyone can use the new mocked function without it being added to @types/jest? My understanding is that the function just returns the input object and all the magic/purpose happens in the typing. Thus I was querying if there's some other way (other than @types/jest) we're supposed to be getting jest types?

[SimenB]

You can use import { jest } from '@jest/globals'; (which is what you must use for native ESM anyways)

[k-rajat19]

these test helper are not depend on @types/jest for their types, all their types are defined in jest-mock.

[samhwang]

One thing I don't understand though is how anyone can use the new mocked function without it being added to @types/jest? My understanding is that the function just returns the input object and all the magic/purpose happens in the typing. Thus I was querying if there's some other way (other than @types/jest) we're supposed to be getting jest types?

hey @cduff, So for the time being, what you can do is this, since the mocked function is already exported in jest-mock anyway.

import { mocked } from 'jest-mock';

these test helper are not depend on @types/jest for their types, all their types are defined in jest-mock.

@k-rajat19 I agree that it's not dependent on @types/jest for their types, but it would be easier (DX-wise) to make it available in the @types/jest package, so the usage can be consistent in TS/JS usage, and also with what is described in the Docs (i.e. you shouldn't need to import jest-mock for the mocked function to work in TS, while it can already work in JS). And then again, this is an issue for the @types/jest package in DefinitelyTyped, not here (like @SimenB said above) :D

[k-rajat19]

@samhwang sorry for being late reply I had not get much time to look here, my exams are going on.
I understand what you want to say that the definitions of mocked function should be included in @types/jest for better DX.

import { mocked } from 'jest-mock';

I don't think you explicitly need to import mocked from jest-mock once you imported jest object.

[samhwang]

I understand what you want to say that the definitions of mocked function should be included in @types/jest for better DX.

I don't think you explicitly need to import mocked from jest-mock once you imported jest object.

@k-rajat19 yes it is like you said: it all depends on how jest's types are being interpreted in the first place, honestly.

If the jest object is being imported from @jest/globals then yeah it's not needed to import mocked from jest-mock explicitly.

But the original issue is for when that's not the case (like if you're not working with ESModules/or just transpile into CommonJS anyway), TS will fill in from using types: ['jest'] in TSConfig, and it will throw an error while doing so. Some rough examples here. And again, this is an issue for @types/jest, not here.

[SimenB]

I don't know why you keep discussing this here - there is absolutely nothing to do in this repo. @types/jest comes from https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/types/jest/index.d.ts, jest.mocked just needs to be added there

[satanTime]

I'm getting an error: https://app.circleci.com/pipelines/github/ike18t/ng-mocks/2810/workflows/cad5fba3-e1c9-4e59-9d20-daf923c60c31/jobs/101406

    TypeError: Cannot read properties of undefined (reading 'bind')

      at Runtime._createJestObjectFor (node_modules/jest-runtime/build/index.js:2193:46)

is it possible that mocked isn't present in some cases?

[SimenB]

Can you open a new issue with a minimal reproduction?

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