Widget test with await is hanged when not using `runAsync` instead of showing error/warning message

[drewwarren]

import "dart:async";

import "package:flutter_test/flutter_test.dart";

void main() {
  Future future;

  setUp(() {
    future = new Future.value();
  });

  testWidgets("awaiting future with value from setUp works",
      (WidgetTester tester) async {
    await future;
  });
}

flutter_test_async$ flutter test test/async_widget_test.dart 
00:05 +0 -1: - awaiting future with value from setUp works                                         
  TimeoutException after 0:00:05.000000: Test timed out after 5 seconds.
  dart:async                _StreamController.add
  websocket_impl.dart 1111  _WebSocketImpl._WebSocketImpl._fromSocket.<fn>
  dart:async                _EventSinkWrapper.add
  websocket_impl.dart 333   _WebSocketProtocolTransformer._messageFrameEnd
  websocket_impl.dart 228   _WebSocketProtocolTransformer.add

00:05 +0 -1: Some tests failed.        

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[Hixie]

testWidgets is using a FakeAsync, and setUp's future is created outside that FakeAsync scope.
I tried reproducing this using only FakeAsync, but couldn't, so I'm not 100% sure what's going on.
@yjbanov any ideas before I try to minimise the heck out of flutter_test? :-)

[yjbanov]

This does look zone-related. I couldn't reproduce using just FakeAsync either. However, what I noticed is that in a plain package:test + FakeAsync test the test zone is a direct child of the setUp zone, but it is a grandchild in a package:flutter_test test.

// package:test
setUp zones: 421730508
test zones: 180409779 < 421730508

// package:flutter_test
setUp zones: 585864271
test zones: 799539283 < 436113664 < 585864271

Here's the plain code I used:

import "dart:async";

import "package:quiver/testing/async.dart";
import "package:test/test.dart";

void main() {
  Future future;

  zoneChain() {
    var zone = Zone.current;
    var zones = [];
    while(zone != null) {
      zones.add(zone);
      zone = zone.parent;
    }
    return zones.map((z) => z.hashCode).join(' < ');
  }

  setUp(() {
    print('setUp zones: ${zoneChain()}');
    future = new Future.value();
  });

  test("awaiting future with value from setUp works", () async {
    var fakeAsync = new FakeAsync();
    fakeAsync.run((_) async {
      print('test zones: ${zoneChain()}');
      await future;
    });
    fakeAsync.flushMicrotasks();
  });
}

[Hixie]

@nex3 any ideas?

[eseidelGoogle]

Do we think this is a package:test bug, should we move it there?

[Hixie]

we've no idea.

[zoechi]

Is this still an issue?

[apaatsio]

From what I understand you are supposed to use tester.runAsync() when you want to test async code like that with testWidgets.

This works:

testWidgets("awaiting future with value from setUp works",
    (WidgetTester tester) async {
  await tester.runAsync(() async {
    await future;
  });
});

Edit: added await to tester.runAsync().

[yjbanov]

I believe @mdebbar saw this recently too. Yes, any real asynchronous work has to go through tester.runAsync(). However, we should try to find a way for tests to not hang, but instead fail with a message complaining about real async work done inside the test. Not sure if that's possible 🤔

[mdebbar]

And don’t forget to await on runAsync:

await tester.runAsync(() async {
  await future;
});

[TahaTesser]

Based on #5728 (comment), test still get hanged when not runAsync so keeping the issue open but #5728 (comment) solves the issue

Code Sample

import "dart:async";

import "package:flutter_test/flutter_test.dart";

void main() {
  Future future;

  setUp(() {
    future = new Future.value();
  });

  testWidgets("awaiting future with value from setUp works",
      (WidgetTester tester) async {
    await tester.runAsync(() async {
      await future;
    });
  });
}

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