Removes error when mocking mongoose library root object

[hluedeke]

Summary

Allows mongoose library to be mocked using jest.mock('mongoose') without the error:

TypeError: Cannot create property 'constructor' on number '1'

Test plan

Used linked forked copy of jest with change with codebase that imported 'mongoose' and the tests ran without errors.

[hluedeke]

Resolves #3073

[SimenB]

Thanks! Would be great to add a test for this. If all existing tests pass, maybe an integration test that has mongoose in it?

---

I merged in master to fix the conflict

[thymikee]

Does this makes us closer to fix the awful recommendation not to use Jest on their docs maybe? https://mongoosejs.com/docs/jest.html

[SimenB]

Wow, harsh :P Hadn't seens the article. Would have been nice if they reached out first...

Meh, not gonna spend any energy on it

[mjesun]

I'm super curious to know which truthy value that is not an object breaks when assigning to it .constructor :)

[hluedeke]

@mjesun #3073 (comment)

[SimenB]

Yeah, just a property called prototype.

This reproduces

const jestMock = require('jest-mock');
const metadata = jestMock.getMetadata({prototype: 1});

jestMock.generateFromMetadata(metadata);

throws:

/Users/simen/repos/jest/packages/jest-mock/build/index.js:684
      mock.prototype.constructor = mock;
                                 ^

TypeError: Cannot create property 'constructor' on number '1'
    at ModuleMockerClass._generateMock (/Users/simen/repos/jest/packages/jest-mock/build/index.js:684:34)
    at ModuleMockerClass.generateFromMetadata (/Users/simen/repos/jest/packages/jest-mock/build/index.js:699:23)
    at Object.<anonymous> (/Users/simen/repos/jest/ugh.js:4:18)
    at Module._compile (internal/modules/cjs/loader.js:689:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:700:10)
    at Module.load (internal/modules/cjs/loader.js:599:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:538:12)
    at Function.Module._load (internal/modules/cjs/loader.js:530:3)
    at Function.Module.runMain (internal/modules/cjs/loader.js:742:12)
    at startup (internal/bootstrap/node.js:283:19)

[SimenB]

I pushed that as a test :)

[hluedeke]

Beat me to it! 😜

[mjesun]

Interestingly, it does not work only on use strict mode:

// Fails:
'use strict'; var x = 1; x.constructor = () => {};

// Works:
var x = 1; x.constructor = () => {};

I guess I'm too old-school by now 😄

[SimenB]

Thanks @hluedeke!

[saveman71]

Hey guys so this comment won't bring anything useful for the conversation, but I just wanted to let you know that because of this we finally can upgrade from mongoose v4.7.0, I've just ran our test suite successfully, and I couldn't be happier today.

Thanks a lot everyone involved, and thank you @hluedeke !!!

You really, really made my day. And kuddos for the fast release. I can't stress enough how it was for me to land on this old issue in our repo, land on this, see "Closed", then see "3 days ago" then go on the PR and see it's merged, and see it's released. Pure joy.

Cheers 🎉

[smably]

Agreed, this was an A+ open source experience! Huge thanks to both @hluedeke and the maintainers for such a quick and friendly fix. Y'all are amazing!

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