flutter error

I'm trying to catch all unhandled exceptions in a Flutter app so I can sent it to a crash reporter. There are instructions on how to do this in the Flutter docs. I followed those, and added two bits of code to my app to catch exceptions:

runZoned<Future<void>>(
() async {
runApp(MyApp());
},
onError: (dynamic error, StackTrace stackTrace) {
print("=================== CAUGHT DART ERROR");
// Send report
},
);
however I got this
════════ Exception Caught By gesture ═══════════════════════════════════════════════════════════════ The following _Exception was thrown while handling a gesture: Exception: Just testing When the exception was thrown, this was the stack:

... etc

how to fix it