`require('./')` broken if parent directory has file with the same name

[vkarpov15]

🐛 Bug Report

Suppose you have a file dir/fn.js that requires the current directory using const x = require('./'), and the parent directory has a file dir.js. In Node.js 8, x will contain the exported value from dir/index.js. In Jest, x will contain the exported value from dir.js

To Reproduce

Steps to reproduce the behavior:

https://github.com/vkarpov15/jest-bug

Expected behavior

require() in Jest should behave the same as require() in vanilla Node.js, especially if using the Node test environment.

Link to repl or repo (highly encouraged)

https://github.com/vkarpov15/jest-bug

envinfo

$ npx envinfo --preset jest
npx: installed 1 in 1.063s

  System:
    OS: Linux 4.15 Ubuntu 16.04.3 LTS (Xenial Xerus)
    CPU: (4) x64 Intel(R) Core(TM) i7-7500U CPU @ 2.70GHz
  Binaries:
    Node: 8.9.4 - /usr/bin/node
    npm: 5.6.0 - /usr/bin/npm
  npmPackages:
    jest: 24.9.0 => 24.9.0 

$ 

Re: Automattic/mongoose#8053

[SimenB]

require should absolutely work the same way in Node. Odd we haven't run into this one before, it's a pretty glaring error...

Would you be able to provide a PR fixing this? The error is probably in https://github.com/facebook/jest/blob/master/packages/jest-resolve/src/defaultResolver.ts

[vkarpov15]

I don't think I have the time to put in a PR. I already worked around this in Mongoose so nothing more to do on my end.

Why does Jest monkey patch require() anyway? Seems very dubious

[jeysal]

It's not really monkey patched, it's a full custom implementation. Used e.g. for the mocking features.

[SimenB]

I don't think I have the time to put in a PR.

That's alright, thanks for the great reproduction case!

Why does Jest monkey patch require() anyway? Seems very dubious

There's no monkey patching involved - we inject a function into the module scope just like node does. The reason we do it is for JIT transpilation and mocking/module mapping. It also allows full isolation between tests without leaking state between them. Granted, it's imperfect, but it's way better nothing