chore: new info on error, readme for jest

Author: Krzysztof Borowy

README.md

@@ -56,6 +56,10 @@ getData = async () => {
 
 See docs for [api and more examples.](docs/API.md)
 
+## Writing tests
+
+If you're writing tests using Jest, check out [the docs on how to integrate it with this module.](./docs/Jest-integration.md)
+
 ## Contribution
 
 See the [CONTRIBUTING](CONTRIBUTING.md) file for how to help out.

lib/AsyncStorage.js

@@ -17,13 +17,14 @@ const RCTAsyncStorage =
   NativeModules.RNC_AsyncSQLiteDBStorage || NativeModules.RNCAsyncStorage;
 
 if (!RCTAsyncStorage) {
-  throw new Error(`@RNCommunity/AsyncStorage: NativeModule.RCTAsyncStorage is null.
+  throw new Error(`[@RNC/AsyncStorage]: NativeModule: AsyncStorage is null.
 
 To fix this issue try these steps:
   • Run \`react-native link @react-native-community/async-storage\` in the project root.
   • Rebuild and re-run the app.
   • Restart the packager with \`--clearCache\` flag.
   • If you are using CocoaPods on iOS, run \`pod install\` in the \`ios\` directory and then rebuild and re-run the app.
+  • If this error shows up while testing with Jest, check out how to mock Async Storage in repository docs.
 
 If none of these fix the issue, please open an issue on the Github repository: https://github.com/react-native-community/react-native-async-storage/issues 
 `);