Stream.periodic usage causes test to hang #40074

kentcb · 2019-09-09T06:39:00Z

I've been trying to get to the bottom of this issue and have honed in on Stream.periodic. In trying to diagnose, I've hit a (probably related) issue, per below.

Steps to Reproduce

import 'dart:async';

import 'package:fake_async/fake_async.dart';
import 'package:flutter_test/flutter_test.dart';

void main() {
  testWidgets('repro with testWidgets (hangs)', (tester) async {
    final periodic = Stream<int>.periodic(const Duration(seconds: 30));
    final subscription = periodic.listen(null);

    await tester.pump(const Duration(seconds: 3));
    await subscription.cancel();

    print('done');
  });

  test('repro with quiver (works)', () async {
    final fakeAsync = FakeAsync();

    // Below I am mimicking the same calls that are made to FakeAsync when using testWidgets
    fakeAsync.flushMicrotasks();
    fakeAsync.flushMicrotasks();
    fakeAsync.flushMicrotasks();

    final periodic = Stream<int>.periodic(const Duration(seconds: 30));
    final subscription = periodic.listen(null);
    fakeAsync.elapse(const Duration(seconds: 3));
    fakeAsync.flushMicrotasks();

    await subscription.cancel();
    print('done');

    fakeAsync.flushMicrotasks();
    fakeAsync.flushMicrotasks();
    fakeAsync.flushMicrotasks();
  });

  // I have no idea why both quiver and fake_async implement a FakeAsync helper or why Flutter uses the former, but I thought I'd try this one as well.
  test('repro with fake_async package (works)', () async {
    fakeAsync((f) async {
      final periodic = Stream<int>.periodic(const Duration(seconds: 30));
      final subscription = periodic.listen(null);
      f.elapse(const Duration(seconds: 3));
      await subscription.cancel();

      print('done');
    });
  });
}

Running the repro with quiver (works) or repro with fake_async package (works) tests both work fine. But running the repro with testWidgets (hangs) test will hang after test execution.

Flutter Doctor

[√] Flutter (Channel stable, v1.9.1+hotfix.4, on Microsoft Windows [Version 10.0.18362.418], locale en-AU)
    • Flutter version 1.9.1+hotfix.4 at C:\Users\Kent\Repository\flutter
    • Framework revision cc949a8e8b (3 weeks ago), 2019-09-27 15:04:59 -0700
    • Engine revision b863200c37
    • Dart version 2.5.0

[√] Android toolchain - develop for Android devices (Android SDK version 29.0.2)
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    • Android NDK location not configured (optional; useful for native profiling support)
    • Platform android-29, build-tools 29.0.2
    • Java binary at: C:\Program Files\Android\Android Studio\jre\bin\java
    • Java version OpenJDK Runtime Environment (build 1.8.0_202-release-1483-b03)
    • All Android licenses accepted.

[√] Android Studio (version 3.5)
    • Android Studio at C:\Program Files\Android\Android Studio
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[√] VS Code (version 1.39.2)
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[!] Connected device
    ! No devices available

! Doctor found issues in 1 category.

The text was updated successfully, but these errors were encountered:

darshankawar · 2020-09-17T12:50:37Z

The test repro with testWidgets (hangs)' still hangs on latest master after completing execution, while other two tests passed without any issues.

flutter doctor -v

[✓] Flutter (Channel master, 1.22.0-10.0.pre.221, on Mac OS X 10.15.4 19E2269
    x86_64, locale en-IN)
    • Flutter version 1.22.0-10.0.pre.221 at
      /Users/dhs/documents/Fluttersdk/flutter
    • Framework revision fa646339d6 (8 hours ago), 2020-09-16 17:47:04 -0700
    • Engine revision 933f811d94
    • Dart version 2.10.0 (build 2.10.0-135.0.dev)

 
[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.0)
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    • Platform android-30, build-tools 30.0.0
    • Java binary at: /Applications/Android
      Studio.app/Contents/jre/jdk/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build
      1.8.0_242-release-1644-b3-6222593)
    • All Android licenses accepted.

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[✓] VS Code (version 1.46.1)
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[✓] Connected device (4 available)
    • SM G975F (mobile)                   • RZ8M802WY0X
      • android-arm64  • Android 10 (API 29)
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      • ios            • com.apple.CoreSimulator.SimRuntime.iOS-13-5 (simulator)
    • Web Server (web)                    • web-server
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    • Chrome (web)                        • chrome
      • web-javascript • Google Chrome 85.0.4183.102

• No issues found!

maheshj01 · 2022-11-23T23:58:52Z

The issue still reproduces as of master 3.6 and stable 3.3

test

import 'dart:async';

import 'package:flutter_test/flutter_test.dart';

void main() {
  testWidgets('repro with testWidgets (hangs)', (tester) async {
    final periodic = Stream<int>.periodic(const Duration(seconds: 10),(count)=>count);
    final subscription = periodic.listen((x){
      print('x: $x');
    });
    await tester.pump(const Duration(seconds: 3));
    await subscription.cancel();

    print('done');
  });
}

flutter doctor -v (mac)

[✓] Flutter (Channel master, 3.6.0-6.0.pre.33, on macOS 12.6 21G115 darwin-arm64,
    locale en-IN)
    • Flutter version 3.6.0-6.0.pre.33 on channel master at
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision a9858ec524 (72 minutes ago), 2022-11-21 10:58:11 -0500
    • Engine revision 46a6b54295
    • Dart version 2.19.0 (build 2.19.0-406.0.dev)
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    • If those were intentional, you can disregard the above warnings; however it is
      recommended to use "git" directly to perform update checks and upgrades.

[✓] Android toolchain - develop for Android devices (Android SDK version 33.0.0-rc4)
    • Android SDK at /Users/mahesh/Library/Android/sdk
    • Platform android-33, build-tools 33.0.0-rc4
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    • Java binary at: /Applications/Android
      Studio.app/Contents/jre/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 11.0.12+0-b1504.28-7817840)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 14.0.1)
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[✓] Connected device (3 available)
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      • com.apple.CoreSimulator.SimRuntime.iOS-14-5 (simulator)
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      • Google Chrome 107.0.5304.110

[✓] HTTP Host Availability
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• No issues found!

[✓] Flutter (Channel stable, 3.3.9, on macOS 12.6 21G115 darwin-arm, locale en-IN)
    • Flutter version 3.3.9 on channel stable at /Users/mahesh/Development/flutter
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision b8f7f1f986 (24 hours ago), 2022-11-23 06:43:51 +0900
    • Engine revision 8f2221fbef
    • Dart version 2.18.5
    • DevTools version 2.15.0

[✓] Android toolchain - develop for Android devices (Android SDK version 33.0.0-rc4)
    • Android SDK at /Users/mahesh/Library/Android/sdk
    • Platform android-33, build-tools 33.0.0-rc4
    • ANDROID_HOME = /Users/mahesh/Library/Android/sdk
    • Java binary at: /Applications/Android Studio.app/Contents/jre/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 11.0.12+0-b1504.28-7817840)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 14.0.1)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Build 14A400
    • CocoaPods version 1.11.3

[✓] Chrome - develop for the web
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Android Studio (version 2021.2)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 11.0.12+0-b1504.28-7817840)

[✓] IntelliJ IDEA Community Edition (version 2021.2.1)
    • IntelliJ at /Applications/IntelliJ IDEA CE.app
    • Flutter plugin version 61.2.4
    • Dart plugin version 212.5080.8

[✓] VS Code (version 1.70.2)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.53.20221101

[✓] Connected device (3 available)
    • iPhone 12 Pro (mobile) • 026D5789-9E78-4AD5-B1B2-3F8D4E7F65E4 • ios            •
      com.apple.CoreSimulator.SimRuntime.iOS-14-5 (simulator)
    • macOS (desktop)        • macos                                • darwin-arm64   • macOS 12.6 21G115 darwin-arm
    • Chrome (web)           • chrome                               • web-javascript • Google Chrome 107.0.5304.110

[✓] HTTP Host Availability
    • All required HTTP hosts are available

• No issues found!

MelbourneDeveloper · 2023-12-11T19:49:25Z

@kentcb the issue has nothing to do with Stream.periodic. The issue happens because the test awaits the cancellation of the subscription. If you don't await the cancellation, Stream.periodic works fine in tests. You can prove this yourself with this sample

import 'dart:async';
import 'package:flutter_test/flutter_test.dart';

void main() {
  testWidgets('Periodic Stream - Working Fine (No Await)', (tester) async {
    final periodic =
        Stream<int>.periodic(const Duration(seconds: 30), (i) => i);
    final subscription = periodic.listen(null);

    await tester.pump(const Duration(seconds: 3));

    //Note here that we don't await and the test passes fine
    subscription.cancel();
  });

    testWidgets('Periodic Stream - Test Hangs (Await Cancel Subscription)', (tester) async {
    final periodic =
        Stream<int>.periodic(const Duration(seconds: 30), (i) => i);
    final subscription = periodic.listen(null);

    await tester.pump(const Duration(seconds: 3));

    //Note here that you can step right over this line and it looks like it executes fine, but it will cause the test to hang
    await subscription.cancel();
  });
}

BondarenkoStas added the a: tests "flutter test", flutter_test, or one of our tests label Sep 9, 2019

This was referenced Dec 4, 2019

Q: why doesn't store have a stream of dispatched actions? fluttercommunity/redux.dart#54

Closed

Q: what is the equivalent of Observable.Create in other RX ecosystems? ReactiveX/rxdart#377

Closed

VladyslavBondarenko added dependency: dart Dart team may need to help us framework flutter/packages/flutter repository. See also f: labels. labels Jan 15, 2020

brianegan mentioned this issue Mar 4, 2020

FakeAsync can't always flush timers properly google/quiver-dart#583

Open

yjbanov mentioned this issue Mar 5, 2020

Sometimes it is impossible to control async work with zones, because some values are tied to root zone dart-lang/sdk#40131

Open

darshankawar added found in release: 1.22 Found to occur in 1.22 has reproducible steps The issue has been confirmed reproducible and is ready to work on passed first triage labels Sep 17, 2020

dotdoom mentioned this issue Apr 1, 2021

WidgetTester.pump inconsistently flushes microtasks #79565

Open

maheshj01 added found in release: 3.3 Found to occur in 3.3 found in release: 3.6 Found to occur in 3.6 and removed found in release: 1.22 Found to occur in 1.22 labels Nov 23, 2022

goderbauer added the P6 label Jan 17, 2023

flutter-triage-bot bot added P3 Issues that are less important to the Flutter project and removed P6 labels Jun 28, 2023

flutter-triage-bot bot added team-framework Owned by Framework team triaged-framework Triaged by Framework team labels Jul 8, 2023

Hixie removed the passed first triage label Jul 8, 2023

huycozy mentioned this issue Dec 11, 2023

Widget Testing - Can't Cancel A Stream Subscription (Package flutter_test) #139870

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Stream.periodic usage causes test to hang #40074

Stream.periodic usage causes test to hang #40074

kentcb commented Sep 9, 2019 •

edited

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darshankawar commented Sep 17, 2020

maheshj01 commented Nov 23, 2022 •

edited

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MelbourneDeveloper commented Dec 11, 2023 •

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Stream.periodic usage causes test to hang #40074

Stream.periodic usage causes test to hang #40074

Comments

kentcb commented Sep 9, 2019 • edited Loading

Steps to Reproduce

Flutter Doctor

darshankawar commented Sep 17, 2020

maheshj01 commented Nov 23, 2022 • edited Loading

MelbourneDeveloper commented Dec 11, 2023 • edited Loading

kentcb commented Sep 9, 2019 •

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maheshj01 commented Nov 23, 2022 •

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MelbourneDeveloper commented Dec 11, 2023 •

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