Add mocks for RNGH

[osdnk]

Motivation

Need to provide some mocks for RNGH in order to make it workable with jest.

Changes

1. Remove need of mocking PlatformConstants. Thanks @tsapeta! Now I check whether PlatformConstants exists before usage.
2. Add mocks of RNGH module.
3. Also abstract RNGH module for separated file for easier mocking.

[ice-chillios]

I've also find out that you may need to mock those:

jest.mock('NativeModules', () => ({
  UIManager: {
    RCTView: () => {}, // or 'View'
  },
  PlatformConstants: {
    forceTouchAvailable: false,
  },
}))

I'm not sure but it may help others :)

[ice-chillios]

Oh, nevermind. You've changed implementation of GestureHandler

[osdnk]

Certainly I do not need PlatformConstants. See the changes and you'll figure out why :).
Why do you think I do need RCTView?

[ice-chillios]

Oh, sorry. This seems to be obsolete. I've had this one in past and thought it's still necessary.

[kmagiera]

Looks good. Can you just comment on how you tested this change? E.g. share a project with jest setup the way it picks up the correct mocks for GH

[osdnk]

I'll share project later. I don't want to have it done in Example because of really strange config, which makes it more difficult and less universal.

[osdnk]

https://github.com/mehranabi/rn-gh-error/blob/master/__tests__/App.js
It's quite useful

[ice-chillios]

@osdnk As you see there it has been necessary to pass the tests. That's why I mentioned this one :)

[osdnk]

@dsznajder
Yes, but https://youtu.be/HG7I4oniOyA?t=115

I see that people are doing it, but I don't want to make it matter of faith. I suppose it was important it previous version because of this:
35c57a0#diff-56d925ec2aada9e1b3b613fe5b782837

But since this commit I see it does not have any impact.

[ice-chillios]

I can confirm that also. It does not make any difference with 1.1.0 and 1.0.17 so I'm pretty sure that your mock is 100% correct ;)

[ice-chillios]

@osdnk I find out that with 1.1.0 and RN 0.59.1 I got an error:
TypeError: Cannot read property 'setJSResponder' of undefined
caused by this line

It seems to be necessary to mock UIManager with an empty object or sth.

[FireyFly]

This should be jestSetup.js, I think? Which probably explains why the jestSetup.js appears to be missing from the 1.2.0 release.

(Also, thanks for this PR/adding this mock--I incidentally ran into issues trying to mock react-native-gesture-handler yesterday, so it landed with quite convenient timing!)