How to test async exception? - flutter-test

Question

I would like to figure out how to test that a widget throws an async exception.
Exception, that is created on the widget's initState:
Future<void> _asyncError() async =>
Future.delayed(Duration(microseconds: 1), () => throw FaultRoots.async);
The test, that does not detect the exception and then throws it:
try {
await tester.pumpWidget(widget);
await tester.pumpAndSettle();
expect(tester.takeException(), isNotNull);
expect(tester.takeException().toString(), contains(p.route));
} catch (ex) {
print(ex.toString());
}
Exception:
══╡ EXCEPTION CAUGHT BY FLUTTER TEST FRAMEWORK ╞════════════════════════════════════════════════════
The following message was thrown running a test:
/fault/async
When the exception was thrown, this was the stack:
#0 _FaultPageState._asyncError.<anonymous closure> (package:flutter_firebase_hello/pages/fault_page.dart:26:55)
#8 FakeTimer._fire (package:fake_async/fake_async.dart:316:16)
#9 FakeAsync._fireTimersWhile (package:fake_async/fake_async.dart:240:13)
#10 FakeAsync.elapse (package:fake_async/fake_async.dart:137:5)
#11 AutomatedTestWidgetsFlutterBinding.pump.<anonymous closure> (package:flutter_test/src/binding.dart:965:28)
#14 TestAsyncUtils.guard (package:flutter_test/src/test_async_utils.dart:72:41)
#15 AutomatedTestWidgetsFlutterBinding.pump (package:flutter_test/src/binding.dart:961:27)
#16 WidgetTester.pumpAndSettle.<anonymous closure> (package:flutter_test/src/widget_tester.dart:640:23)
<asynchronous suspension>
<asynchronous suspension>
(elided 10 frames from dart:async and package:stack_trace)

Answer 1

Async exceptions can be caught by runZonedGuarded:
await runZonedGuarded(() async {
await tester.pumpWidget(makeTestable(widget));
await tester.pumpAndSettle();
}, (error, stack) {
... error validation ...
});