jest.Global incorrectly extends interface 'NodeJS.Global'?

[bartekleon]

Hello dear Jest fellows,
i've been doing some maintenance stuff in stryker-mutator and came into this error:

packages/jest-runner/node_modules/@jest/types/build/Global.d.ts:54:18 - error TS2430: Interface 'import("/home/travis/build/stryker-mutator/stryker/packages/jest-runner/node_modules/@jest/types/build/Global").Global' incorrectly extends interface 'NodeJS.Global'.
  Types of property 'describe' are incompatible.
    Type 'Describe' is not assignable to type 'SuiteFunction'.
      Types of property 'only' are incompatible.
        Type 'DescribeBase' is not assignable to type 'ExclusiveSuiteFunction'.
          Type 'void' is not assignable to type 'Suite'.
54 export interface Global extends NodeJS.Global {

We don't get any other error related to that so I am not sure why is it occurring (all i have done is to change dependencies from jest: ^24.9.0 to ~24.9)

Do you have any idea why it happened?

link to a PR: stryker-mutator/stryker-js#1706
link to a one of travis jobs: https://travis-ci.org/stryker-mutator/stryker/jobs/582083380

[thymikee]

@jeysal would you mind taking a look?

[SimenB]

We don't get that error when building (using the latest TS 3.6), but maybe it's an issue with older versions of TS?

all i have done is to change dependencies from jest: ^24.9.0 to ~24.9

24.9.0 is the latest 24 release, so just changing that part wouldn't make a difference. Something else changed. I'd take a look at any lockfiles you might have.

[jeysal]

Looks like a conflict with another framework defining the describe global

[bartekleon]

Probably it is conflicting with mocha since i have seen some errors like 'it' has already been declared

[aqumus]

@kmdrGroch U happen to find any resolution, as even in one of my project, getting same error

[bartekleon]

I think it was related that both jest and mocha (and more test runners/frameworks) were installed in the same project. I guess there was some problems with namespaces and so typescript assumed that these functions were defined in several places. So I can say it is solved.

[bartekleon]

@aqumus try npm prune or remove / reinstall test frameworks / runners if you have more than 1

[drudv]

I had a similar issue because there was another node_modules folder on top of my project's folder. The errors disappeared, when I removed those node_modules.

[bartekleon]

I think it can be closed with these solutions :)

[codeviking]

We ran into this recently. Ultimately it was because:

• We were using mocha as a test runner.
• We added expect, which depends on @jest.
• @jest defines describe, here: https://github.com/facebook/jest/blob/master/packages/jest-types/src/Global.ts#L76
• @types/mocha defines describe as well, here: https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/types/mocha/index.d.ts#L598
• The two describes aren't compatible, so TypeScript ends up being unhappy.

Our solution was to replace expect with chai, as it doesn't depend upon @jest. We could've also likely replaced mocha with jest, but that felt like a larger effort.

[SimenB]

This was fixed in Jest@25 (and expect@25) btw - it should play nice with mocha's global definitions. #9415

[codeviking]

@SimenB Great! I confirmed that expect@25 resolved the issue.

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