Flutter: How to implement FlutterError.OnError correctly - dart

Question

Can someone show me how to implement overriding flutter errors during widget test so I can check for my own custom errors.
I have seen snippets online mentioning this but all of my implementations fail
void main() {
testWidgets('throws an error when scanning unknown term types', (WidgetTester tester) async {
await tester.pumpWidget(injectTestWidget(new ItemScanScreen()));
await tester.enterText(find.byKey(new Key('term')), '');
await tester.tap(find.byIcon(Icons.send));
await tester.pump();
expect(
tester.takeException(),
isInstanceOf<UnrecognizedTermException>(),
reason: 'should have thrown an UnrecognizedTermException error but didn\'t',
);
});
}
the code above fails with the message below even though it looks like it in fact 'caught' my error:
The following UnrecognizedTermException was thrown running a test:
Instance of 'UnrecognizedTermException'
...
I read that you could do something like the snippet below but it did not see how/where to implement it:
final errorHandled = expectAsync0((){});
FlutterError.onError = (errorDetails) {
// handle error
errorHandled();
});

Answer 1

I use the code below in production to log errors to a server.
main.dart:
import 'dart:async';
import 'package:flutter/material.dart';
import 'logging.dart';
void main() async {
FlutterError.onError = (FlutterErrorDetails details) async {
new ErrorLogger().logError(details);
};
runZoned<Future<void>>(() async {
// Your App Here
runApp(MainApp());
}, onError: (error, stackTrace) {
new ErrorLogger().log(error, stackTrace);
});
}
logging.dart:
class ErrorLogger {
void logError(FlutterErrorDetails details) async {
//FlutterError.dumpErrorToConsole(details);
_sendToServer(details.exceptionAsString(), details.stack.toString());
}
void log(Object data, StackTrace stackTrace) async {
// print(data);
// print(stackTrace);
_sendToServer(data.toString(), stackTrace.toString());
}
void _sendToServer(String a, String b) async {
// Implementation here
}
}

Answer 2

This is was design for a test. I switched to wrapping logic in try/catch then running expect() on the "error message text" present concept. ex:
try {
throw new UnrecognizedTermException();
} catch (e) {
setState(() => _status = e.errMsg());
}
// then in my test
expect(find.text('Could not determine the type of item you scanned'), findsOneWidget);