Update testing section

[kligarski]

This PR is a continuation of (#1374).

Description

Adding examples to the testing section of the documentation ("Testing with Jest").

Changes

• changed setup of mocking react-native-reanimated and added a link to the docs of Reanimated,
• added example of mocking react-native-screens (from previous PR),
• added new real-life examples:
  • navigation between tabs (simple tab change, without fake timers),
  • reacting to navigation events (text showing after animation ends (stack naviagator), fake timers introduced),
  • example with stack, tabs and tabPress,
  • example with useFocusEffect and data fetching
    • there is a problem with warnings when running the test (Update testing section #1404 (comment))
• fixed getBy vs queryBy according to the suggestion from the previous PR (Update testing section #1374 (comment))

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[kligarski]

In the Example 4, adding jest.useFakeTimers() even without running the timers fixes an issue with React state update warnings from React Testing Library (they sometimes appear when running the test). I tried wrapping various parts of the test in act with no success. I suspect it is connected with fetching the data asynchronously but I'm not sure what the issue is exactly and why using fake timers helps with this problem.

[kligarski]

@kkafar

[kkafar]

Looks good to me! I've added few suggestions & changes requests.

IMO this is is.

I'll want to get input from @satya164 before merging though.

[kkafar]

We need to improve the PR description slightly before we land it.
Other than that - great job. Also shoutout to @AnCichocka for the bulk of the work.

[kligarski]

PR description updated.