🔧 Fix recently introduced code regressions

[sebranly]

Overview

Previously, two regressions were introduced as a compromise:

• 🐙 Use React Testing Library (adapted for react-native) #42 (comment)
• 🐙 Use React Testing Library (adapted for react-native) #42 (comment)

Now, both regressions are fixed.

Testing

• npm run test should be ✅
• App should be available on a real device (iPhone) after running npm run start

Additional information

For App/index.tsx I decided to use an initialReady props only for tests (so it's set to false if not present, for same behavior as what the app used to do). I could also have added an && process.env['NODE_ENV'] !== 'test' condition to the short-circuit (instead) but I find it a bit dirty. Reason behind all of it is that it looks difficult to simulate useEffect with react-native + the testing library (note: I tried out rerender to no luck): testing-library/react-testing-library#215