Check if flutter testWidgets supports multiple isolates

isolate_test.dart

import 'dart:async';
import 'dart:isolate';

import 'package:flutter_test/flutter_test.dart';

void main() {
  testWidgets('Headers', (WidgetTester tester) async {
    final Completer<String> completer = Completer<String>();

    final RawReceivePort receivePort = RawReceivePort((dynamic message) {
      print('received message $message');
      completer.complete(message);
    });
    await Isolate.spawn(f, [[123], receivePort.sendPort]);
    expect(await completer.future, equals('abc'));
    receivePort.close();
  }, skip: isBrowser);
}

void f(List<dynamic> params) {
  final List<int> l = params[0];
  final SendPort s = params[1];
  print('Received $l');
  s.send('abc');
}

This test never finishes and prints the following:

Testing started at 07:38 ...
flutter/bin/flutter --no-color test --machine --start-paused test/widgets/isolate_test.dart
Shell: Received [123]
Shell: received message abc

So await at line 15 never seems to get completer completed.