Service.getInfo() does not work for test environment.

[polina-c]

Steps to repro:

clone [email protected]:polina-c/spikes.git
cd spikes/connect_vm
flutter test test/widget_test.dart

See output Obtaining info... and the test never finishes.

The output is from the code:

    print('Obtaining info...');
    final info = await Service.getInfo();
    print('Obtained info.');

There is no error as well.

[polina-c]

If I run the test by clicking 'Debug' in VSCode, I can successfully connect to the isolate with DEvTools, when test is paused, using url printed in debug console:

[polina-c]

Screen.Recording.2023-05-10.at.4.41.20.PM.mov

[polina-c]

@bkonyi @a-siva @rmacnak-google

[bkonyi]

So I've done some digging and I'm not sure exactly what's going on here. The call to the service isolate to get the URI completes successfully and the receivePort.handler is executing completer.complete(uriString). However, the completer's future isn't completing so we hang:

static Future<ServiceProtocolInfo> getInfo() async {
  // Port to receive response from service isolate.
  final RawReceivePort receivePort =
      new RawReceivePort(null, 'Service.getInfo');
  final Completer<String?> completer = new Completer<String?>();
  receivePort.handler = (String? uriString) {
    // This callback executes
    completer.complete(uriString);
  };
  // Request the information from the service isolate.
  _getServerInfo(receivePort.sendPort);
  // Await the response from the service isolate.

  //!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
  // **This future never completes**
  //!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
  String? uriString = await completer.future;

  Uri? uri = uriString == null ? null : Uri.parse(uriString);
  // Close the port.
  receivePort.close();
  return new ServiceProtocolInfo(uri);
}

I wonder the event loop in flutter_tester is configured differently or does some weird stuff with futures. @christopherfujino, would you know anything about this or know who might?

[bkonyi]

@mraleph correctly identified this as an issue related to the use of FakeAsync in flutter_tester. The fix is to wrap the call to Service.getInfo() in tester.runAsync.