docs: update docs on custom jest preset (#1316)

* docs: update docs on custom jest preset

* docs: flip conditions on modern timers and react native version

* Update README.md

Co-authored-by: Maciej Jastrzebski <[email protected]>

* Update title in readme for custom jest preset

Co-authored-by: Maciej Jastrzebski <[email protected]>

---------

Co-authored-by: pierrezimmermann <[email protected]>
Co-authored-by: Maciej Jastrzebski <[email protected]>

Author: 3 people

README.md

@@ -72,11 +72,11 @@ Then automatically add it to your jest tests by using `setupFilesAfterEnv` optio
 }
 ```
 
-### Custom Jest Preset
+### Custom Jest Preset (React Native before 0.71)
 
-> **important** if you use "modern" Fake Timers
+We generally advise to use the "react-native" preset when testing with this library.
 
-We generally advise to use the "react-native" preset when testing with this library. However, if you use ["modern" Fake Timers](https://jestjs.io/blog/2020/05/05/jest-26#new-fake-timers) (default since Jest 27), you'll need to apply our custom Jest preset or awaiting promises, like `waitFor`, will timeout.
+However, if you use React Native version earlier than 0.71 with [modern Jest fake timers](https://jestjs.io/blog/2020/05/05/jest-26#new-fake-timers) (default since Jest 27), you'll need to apply this custom Jest preset or otherwise awaiting promises, like using `waitFor` or `findBy*`, queries will fail with timeout.
 
 This is a [known issue](https://github.com/facebook/react-native/issues/29303). It happens because React Native's Jest preset overrides native Promise. Our preset restores it to defaults, which is not a problem in most apps out there.
 

website/docs/API.md

@@ -579,10 +579,10 @@ Avoiding side effects in `expectation` callback can be partially enforced with t
 
 It is also recommended to have a [single assertion per each `waitFor`](https://kentcdodds.com/blog/common-mistakes-with-react-testing-library#having-multiple-assertions-in-a-single-waitfor-callback) for more consistency and faster failing tests. If you want to make several assertions, then they should be in seperate `waitFor` calls. In many cases you won't actually need to wrap the second assertion in `waitFor` since the first one will do the waiting required for asynchronous change to happen.
 
-### Using Jest fake timers
+### Using a React Native version < 0.71 with Jest fake timers
 
 :::caution
-When using modern fake timers (the default for `Jest` >= 27), `waitFor` won't work (it will always timeout even if `expectation()` doesn't throw) unless you use the custom [@testing-library/react-native preset](https://github.com/callstack/react-native-testing-library#custom-jest-preset). 
+When using a version of React Native < 0.71 and modern fake timers (the default for `Jest` >= 27), `waitFor` won't work (it will always timeout even if `expectation()` doesn't throw) unless you use the custom [@testing-library/react-native preset](https://github.com/callstack/react-native-testing-library#custom-jest-preset). 
 :::
 
 `waitFor` checks whether Jest fake timers are enabled and adapts its behavior in such case. The following snippet is a simplified version of how it behaves when fake timers are enabled: