Add jest mock for the Linking library

[Maxwell2022]

Motivation

This PR is adding a mock of the React Native library Linking. Some of the third party library are expecting this Module to be mocked. If not mocked, jest test is throwing the following error:

● Test suite failed to run

Invariant Violation: Native module cannot be null.

  at invariant (node_modules/fbjs/lib/invariant.js:44:15)
  at Linking.NativeEventEmitter (node_modules/react-native/Libraries/EventEmitter/NativeEventEmitter.js:32:1)
  at new Linking (node_modules/react-native/Libraries/Linking/Linking.js:119:141)
  at Object.<anonymous> (node_modules/react-native/Libraries/Linking/Linking.js:191:16)
  at Object.get Linking [as Linking] (node_modules/react-native/Libraries/react-native/react-native.js:90:22)
  at Object.<anonymous> (node_modules/react-native-experimental-navigation/NavigationRootContainer.js:15:36)

Test Plan

There are no tests for mocks. Actual tests are not broken after adding this mock

Additional Information

The current workaround is to have your own jest-setup.js, that need to be added in the jest configuration, with the following mock:

jest.mock('Linking', () => ({
  addEventListener: jest.fn(),
  removeEventListener: jest.fn(),
  openURL: jest.fn(),
  canOpenURL: jest.fn(),
  getInitialURL: jest.fn(),
}));

And in your package.json:

"jest": {
  "preset": "react-native",
  "setupFiles": [
    "./node_modules/react-native/jest/setup.js",
    "./jest-setup.js"
  ]
}

[javache]

Please mock startObserving and stopObserving instead of these two.

[Maxwell2022]

I'm confused, these methods are not exposed in the Linking library:
Libraries/Linking/Linking.js:127

[javache]

No, but they are on the NativeModule (and used by EventEmitter)

[javache]

Will need to be rebased on #12839

[javache]

Looks like something went wrong with your rebase. Please verify your diff looks correct.

[Maxwell2022]

That's weird, when I rebase my branch to master it says that I'm 84 ahead, 69 behind.
I just ran git rebase master jest-mock-linking

Not sure whatI'm missing here

[Maxwell2022]

I don't know why it's messed up but I think this PR doesn't make sense anymore as it has been implemented in other PRs. Just closing it