[Bug] Yarn 2 PnP and peer dependencies in Jest tests in workspace

• I’d be willing to implement a fix

Describe the bug

Peer dependencies of packages cannot be found when running Jest tests in workspace.

To Reproduce

I have created following minimal setup: https://github.com/kirill-konshin/yarn-berry-bug

Steps to reproduce:

$ git clone https://github.com/kirill-konshin/yarn-berry-bug.git
$ yarn
$ cd ws
$ yarn test

Output:

xxx@xxx ws % yarn test
 FAIL  src/index.test.js
  ● Test suite failed to run

    Cannot find module 'react' from 'index.js'

    However, Jest was able to find:
        './Router.js'

    You might want to include a file extension in your import, or update your 'moduleFileExtensions', which is currently ['js', 'json', 'jsx', 'ts', 'tsx', 'node'].

    See https://jestjs.io/docs/en/configuration#modulefileextensions-array-string

      at Resolver.resolveModule (../.yarn/cache/jest-resolve-npm-25.1.0-2276a075e4-2.zip/node_modules/jest-resolve/build/index.js:276:11)
      at Object.<anonymous> (../.yarn/cache/create-react-class-npm-15.6.3-ae38dfa180-2.zip/node_modules/create-react-class/index.js:11:13)

Test Suites: 1 failed, 1 total
Tests:       0 total
Snapshots:   0 total
Time:        1.293s
Ran all test suites.

It looks like in the following setup require of react-router causes require of react in that module which can’t be found. Works perfect without PNP. Adding jest-pnp-resolver does not help.

Environment if relevant (please complete the following information):

• OS: Mac
• Node version: 12.11.1
• Yarn version: 2.0.0-rc.29

[arcanis]

Jest is “lying” and hiding the error that Yarn throws. It becomes very visible if you run your application with PNP_DEBUG_LEVEL=1 in your environment:

As you can see, the true error is:

error: Error: A package is trying to access another package without the second one being listed as a dependency of the first one

Required package: react (via "react")
Required by: create-react-class@npm:15.6.3 (via /home/arcanis/yarn-berry-bug/.yarn/cache/create-react-class-npm-15.6.3-ae38dfa180-2.zip/node_modules/create-react-class/)

By looking into the sources for create-react-class, we can see that they forgot to list the react peer dependency, hence why the resolution fails. Adding a packageExtensions entry fixes the issue:

packageExtensions:
    "create-react-class@*":
        peerDependencies:
            react: "*"

[kirill-konshin]

Done https://github.com/facebook/jest/issues/9594