Undocumented breaking change with moduleDirectories config in Jest v20

[lourd]

Hey y'all, congrats on the release of v20! A lot of really great additions, as well as critical, less-flashy work refactoring for the future. Thank you for your efforts 🙏🏼

Just updated a couple projects and ran into an undocumented breaking change. It's not really an issue to fix, but I want to document it for other folks who run into it.

After upgrading from v19 to v20 I had all of my tests failing with various Cannot find module errors. First it was coming from a script loading polyfills so I was seeing Cannot find module 'babel-polyfill' from 'polyfills.js', so I thought it was part of the changes to Jest no longer loading babel-polyfill internally. I commented that file out though and got Cannot find module 'once' from 'queueRunner.js', which was definitely not in my codebase. At that point I started playing around with some config changes to see what might affect it.

Turned out to be the moduleDirectories configuration. I've been using "<rootDir>" in each entry, which doesn't seem to be valid any longer. Once I dropped that prefix that fixed everything.

     "moduleDirectories": [
-      "<rootDir>/app/",
-      "<rootDir>/node_modules/"
+      "app",
+      "node_modules"
     ],

[cpojer]

Thank you! This is actually a regression and we'll fix it in a patch release.

[pcvandamcb]

Not sure if the same regression, but this also does not work anymore in v20:

"testMatch": [
  "<rootDir>/tests/frontend-unit/**/*Test.js"
]

Problem is, without the <rootDir> I also can't get the glob to work anymore.

[cpojer]

We should also fix that one, yes. Thanks for mentioning it.

[ismay]

Maybe it's not necessary that I mention this, but this also failed for me after upgrading to v20:

{
  "snapshotSerializers": [
    "<rootDir>/node_modules/jest-serializer-enzyme"
  ]
}

[cpojer]

Fixed in the latest patch.

[github-actions]

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