Fix NativeModules.RNSnackbar being undefined during testing

[arakawamoriyuki]

problem

Test fails with NativeModules.RNSnackbar undefined.

Cannot read property 'LENGTH_LONG' of undefined

env

• react-native 0.47.1
• react-native-snackbar 0.4.4

fixes

Fix to not use if undefined.

related issues

• Cannot read property 'LENGTH_LONG' of undefined

[cooperka]

Hi @arakawamoriyuki, thank you for the contribution! But I think most native modules actually work this way -- I suggest you mock it out instead of modifying the code here. For example, with Jest: https://facebook.github.io/jest/docs/en/manual-mocks.html

// your-app/__mocks__/react-native-snackbar.js

module.exports = {
  LENGTH_LONG: 0,
  LENGTH_SHORT: -1,
  LENGTH_INDEFINITE: -2,
};

or without Jest you could manually shim (I haven't tested this myself):

// your-app/run-this-before-your-tests.js

import { NativeModules } from 'react-native'

NativeModules.RNSnackbar = {
  LENGTH_LONG: 0,
  LENGTH_SHORT: -1,
  LENGTH_INDEFINITE: -2,
};

I'm happy to merge this PR if it is, in fact, some sort of standard to export something different during testing, but in my experience, this change would be unexpected behavior. It could break other peoples' tests who may have shimmed NativeModules.RNSnackbar.

[arakawamoriyuki]

thank you for the advice. The test worked with the app/__mocks__/react-native-snackbar.js.