React Native + Jest: Cannot find module 'react-dom' from 'mobxreact.cjs.development.js'

[jayshah123]

Having a fairly barebones react-native + mobx setup here (https://github.com/jayshah123/mobx-jest-test-error)
Running npm test asks forreact-dom dependency.

Intended outcome

Jest test should run as expected

Actual outcome

Test fails saying: Cannot find module 'react-dom' from 'mobxreact.cjs.development.js'

Full error:

bash-3.2$ npm test

> [email protected] test /Users/jay.shah/Documents/sampleapps/JestMobxChecker
> jest

 FAIL  __tests__/App-test.js
  ● Test suite failed to run

    Cannot find module 'react-dom' from 'mobxreact.cjs.development.js'

    However, Jest was able to find:
        './ColorComponent.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

    However, Jest was able to find:
        '../App.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 (node_modules/jest-resolve/build/index.js:276:11)
      at Object.<anonymous> (node_modules/mobx-react/dist/mobxreact.cjs.development.js:10:16)

Test Suites: 1 failed, 1 total
Tests:       0 total
Snapshots:   0 total
Time:        1.401s
Ran all test suites.
npm ERR! Test failed.  See above for more details.

How to reproduce the issue

https://github.com/jayshah123/mobx-jest-test-error

1. clone the repo
2. npm install
3. npm test

Versions

    "mobx": "^5.15.4",
    "mobx-react": "^6.1.8",
    "react": "16.9.0",
    "react-native": "0.61.5"

[danielkcz]

This will be generally solved by #787 once I get to finishing it up :)

For now, you basically have to force mobx-react in Jest config to resolve to RN bundle instead of regular CJS one.

Hm, that might not actually work because RN bundle uses ESM which Jest cannot handle afaik. Cannot think of any viable workaround for now so I guess it makes #787 fairly important now :)

[vonovak]

@jayshah123 this PR makes the test run jayshah123/mobx-jest-test-error#1 . I didn't go any further than that though, so not sure if some more complicated tests relying on mobx will work too.)

[danielkcz]

Please, upgrade to mobx-react 6.2.0 and see instructions in the readme.

[lock]

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