widget_tester_test.dart

// Copyright 2014 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'dart:async';
import 'dart:io';

import 'package:flutter/cupertino.dart';
import 'package:flutter/foundation.dart';
import 'package:flutter/gestures.dart';
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
import 'package:flutter/scheduler.dart';
import 'package:flutter_test/flutter_test.dart';
import 'package:test_api/src/expect/async_matcher.dart'; // ignore: implementation_imports
// ignore: deprecated_member_use
import 'package:test_api/test_api.dart' as test_package;

const List<Widget> fooBarTexts = <Text>[
  Text('foo', textDirection: TextDirection.ltr),
  Text('bar', textDirection: TextDirection.ltr),
];

void main() {
  group('expectLater', () {
    testWidgets('completes when matcher completes', (WidgetTester tester) async {
      final Completer<void> completer = Completer<void>();
      final Future<void> future = expectLater(null, FakeMatcher(completer));
      String? result;
      future.then<void>((void value) {
        result = '123';
      });
      test_package.expect(result, isNull);
      completer.complete();
      test_package.expect(result, isNull);
      await future;
      await tester.pump();
      test_package.expect(result, '123');
    });

    testWidgets('respects the skip flag', (WidgetTester tester) async {
      final Completer<void> completer = Completer<void>();
      final Future<void> future = expectLater(null, FakeMatcher(completer), skip: 'testing skip');
      bool completed = false;
      future.then<void>((_) {
        completed = true;
      });
      test_package.expect(completed, isFalse);
      await future;
      test_package.expect(completed, isTrue);
    });
  });

  group('respects the group skip flag', () {
    testWidgets('should be skipped', (WidgetTester tester) async {
      expect(false, true);
    });
  }, skip: true);

  group('findsOneWidget', () {
    testWidgets('finds exactly one widget', (WidgetTester tester) async {
      await tester.pumpWidget(const Text('foo', textDirection: TextDirection.ltr));
      expect(find.text('foo'), findsOneWidget);
    });

    testWidgets('fails with a descriptive message', (WidgetTester tester) async {
      late TestFailure failure;
      try {
        expect(find.text('foo', skipOffstage: false), findsOneWidget);
      } on TestFailure catch (e) {
        failure = e;
      }

      expect(failure, isNotNull);
      final String? message = failure.message;
      expect(message, contains('Expected: exactly one matching node in the widget tree\n'));
      expect(message, contains('Actual: _TextFinder:<zero widgets with text "foo">\n'));
      expect(message, contains('Which: means none were found but one was expected\n'));
    });
  });

  group('findsNothing', () {
    testWidgets('finds no widgets', (WidgetTester tester) async {
      expect(find.text('foo'), findsNothing);
    });

    testWidgets('fails with a descriptive message', (WidgetTester tester) async {
      await tester.pumpWidget(const Text('foo', textDirection: TextDirection.ltr));

      late TestFailure failure;
      try {
        expect(find.text('foo', skipOffstage: false), findsNothing);
      } on TestFailure catch (e) {
        failure = e;
      }

      expect(failure, isNotNull);
      final String? message = failure.message;

      expect(message, contains('Expected: no matching nodes in the widget tree\n'));
      expect(message, contains('Actual: _TextFinder:<exactly one widget with text "foo": Text("foo", textDirection: ltr)>\n'));
      expect(message, contains('Which: means one was found but none were expected\n'));
    });

    testWidgets('fails with a descriptive message when skipping', (WidgetTester tester) async {
      await tester.pumpWidget(const Text('foo', textDirection: TextDirection.ltr));

      late TestFailure failure;
      try {
        expect(find.text('foo'), findsNothing);
      } on TestFailure catch (e) {
        failure = e;
      }

      expect(failure, isNotNull);
      final String? message = failure.message;

      expect(message, contains('Expected: no matching nodes in the widget tree\n'));
      expect(message, contains('Actual: _TextFinder:<exactly one widget with text "foo" (ignoring offstage widgets): Text("foo", textDirection: ltr)>\n'));
      expect(message, contains('Which: means one was found but none were expected\n'));
    });
  });

  group('pumping', () {
    testWidgets('pumping', (WidgetTester tester) async {
      await tester.pumpWidget(const Text('foo', textDirection: TextDirection.ltr));
      int count;

      final AnimationController test = AnimationController(
        duration: const Duration(milliseconds: 5100),
        vsync: tester,
      );
      count = await tester.pumpAndSettle(const Duration(seconds: 1));
      expect(count, 1); // it always pumps at least one frame

      test.forward(from: 0.0);
      count = await tester.pumpAndSettle(const Duration(seconds: 1));
      // 1 frame at t=0, starting the animation
      // 1 frame at t=1
      // 1 frame at t=2
      // 1 frame at t=3
      // 1 frame at t=4
      // 1 frame at t=5
      // 1 frame at t=6, ending the animation
      expect(count, 7);

      test.forward(from: 0.0);
      await tester.pump(); // starts the animation
      count = await tester.pumpAndSettle(const Duration(seconds: 1));
      expect(count, 6);

      test.forward(from: 0.0);
      await tester.pump(); // starts the animation
      await tester.pump(); // has no effect
      count = await tester.pumpAndSettle(const Duration(seconds: 1));
      expect(count, 6);
    });

    testWidgets('pumpFrames', (WidgetTester tester) async {
      final List<int> logPaints = <int>[];
      int? initial;

      final Widget target = _AlwaysAnimating(
        onPaint: () {
          final int current = SchedulerBinding.instance!.currentFrameTimeStamp.inMicroseconds;
          initial ??= current;
          logPaints.add(current - initial!);
        },
      );

      await tester.pumpFrames(target, const Duration(milliseconds: 55));

      expect(logPaints, <int>[0, 17000, 34000, 50000]);
      logPaints.clear();

      await tester.pumpFrames(target, const Duration(milliseconds: 30), const Duration(milliseconds: 10));

      expect(logPaints, <int>[60000, 70000, 80000]);
    });
  });

  group('find.byElementPredicate', () {
    testWidgets('fails with a custom description in the message', (WidgetTester tester) async {
      await tester.pumpWidget(const Text('foo', textDirection: TextDirection.ltr));

      const String customDescription = 'custom description';
      late TestFailure failure;
      try {
        expect(find.byElementPredicate((_) => false, description: customDescription), findsOneWidget);
      } on TestFailure catch (e) {
        failure = e;
      }

      expect(failure, isNotNull);
      expect(failure.message, contains('Actual: _ElementPredicateFinder:<zero widgets with $customDescription'));
    });
  });

  group('find.byWidgetPredicate', () {
    testWidgets('fails with a custom description in the message', (WidgetTester tester) async {
      await tester.pumpWidget(const Text('foo', textDirection: TextDirection.ltr));

      const String customDescription = 'custom description';
      late TestFailure failure;
      try {
        expect(find.byWidgetPredicate((_) => false, description: customDescription), findsOneWidget);
      } on TestFailure catch (e) {
        failure = e;
      }

      expect(failure, isNotNull);
      expect(failure.message, contains('Actual: _WidgetPredicateFinder:<zero widgets with $customDescription'));
    });
  });

  group('find.descendant', () {
    testWidgets('finds one descendant', (WidgetTester tester) async {
      await tester.pumpWidget(Row(
        textDirection: TextDirection.ltr,
        children: <Widget>[
          Column(children: fooBarTexts),
        ],
      ));

      expect(find.descendant(
        of: find.widgetWithText(Row, 'foo'),
        matching: find.text('bar'),
      ), findsOneWidget);
    });

    testWidgets('finds two descendants with different ancestors', (WidgetTester tester) async {
      await tester.pumpWidget(Row(
        textDirection: TextDirection.ltr,
        children: <Widget>[
          Column(children: fooBarTexts),
          Column(children: fooBarTexts),
        ],
      ));

      expect(find.descendant(
        of: find.widgetWithText(Column, 'foo'),
        matching: find.text('bar'),
      ), findsNWidgets(2));
    });

    testWidgets('fails with a descriptive message', (WidgetTester tester) async {
      await tester.pumpWidget(Row(
        textDirection: TextDirection.ltr,
        children: <Widget>[
          Column(children: const <Text>[Text('foo', textDirection: TextDirection.ltr)]),
          const Text('bar', textDirection: TextDirection.ltr),
        ],
      ));

      late TestFailure failure;
      try {
        expect(find.descendant(
          of: find.widgetWithText(Column, 'foo'),
          matching: find.text('bar'),
        ), findsOneWidget);
      } on TestFailure catch (e) {
        failure = e;
      }

      expect(failure, isNotNull);
      expect(
        failure.message,
        contains(
          'Actual: _DescendantFinder:<zero widgets with text "bar" that has ancestor(s) with type "Column" which is an ancestor of text "foo"',
        ),
      );
    });
  });

  group('find.ancestor', () {
    testWidgets('finds one ancestor', (WidgetTester tester) async {
      await tester.pumpWidget(Row(
        textDirection: TextDirection.ltr,
        children: <Widget>[
          Column(children: fooBarTexts),
        ],
      ));

      expect(find.ancestor(
        of: find.text('bar'),
        matching: find.widgetWithText(Row, 'foo'),
      ), findsOneWidget);
    });

    testWidgets('finds two matching ancestors, one descendant', (WidgetTester tester) async {
      await tester.pumpWidget(
        Directionality(
          textDirection: TextDirection.ltr,
          child: Row(
            children: <Widget>[
              Row(children: fooBarTexts),
            ],
          ),
        ),
      );

      expect(find.ancestor(
        of: find.text('bar'),
        matching: find.byType(Row),
      ), findsNWidgets(2));
    });

    testWidgets('fails with a descriptive message', (WidgetTester tester) async {
      await tester.pumpWidget(Row(
        textDirection: TextDirection.ltr,
        children: <Widget>[
          Column(children: const <Text>[Text('foo', textDirection: TextDirection.ltr)]),
          const Text('bar', textDirection: TextDirection.ltr),
        ],
      ));

      late TestFailure failure;
      try {
        expect(find.ancestor(
          of: find.text('bar'),
          matching: find.widgetWithText(Column, 'foo'),
        ), findsOneWidget);
      } on TestFailure catch (e) {
        failure = e;
      }

      expect(failure, isNotNull);
      expect(
        failure.message,
        contains(
          'Actual: _AncestorFinder:<zero widgets with type "Column" which is an ancestor of text "foo" which is an ancestor of text "bar"',
        ),
      );
    });

    testWidgets('Root not matched by default', (WidgetTester tester) async {
      await tester.pumpWidget(Row(
        textDirection: TextDirection.ltr,
        children: <Widget>[
          Column(children: fooBarTexts),
        ],
      ));

      expect(find.ancestor(
        of: find.byType(Column),
        matching: find.widgetWithText(Column, 'foo'),
      ), findsNothing);
    });

    testWidgets('Match the root', (WidgetTester tester) async {
      await tester.pumpWidget(Row(
        textDirection: TextDirection.ltr,
        children: <Widget>[
          Column(children: fooBarTexts),
        ],
      ));

      expect(find.descendant(
        of: find.byType(Column),
        matching: find.widgetWithText(Column, 'foo'),
        matchRoot: true,
      ), findsOneWidget);
    });
  });

  group('pageBack', () {
    testWidgets('fails when there are no back buttons', (WidgetTester tester) async {
      await tester.pumpWidget(Container());

      expect(
        expectAsync0(tester.pageBack),
        throwsA(isA<TestFailure>()),
      );
    });

    testWidgets('successfully taps material back buttons', (WidgetTester tester) async {
      await tester.pumpWidget(
        MaterialApp(
          home: Center(
            child: Builder(
              builder: (BuildContext context) {
                return ElevatedButton(
                  child: const Text('Next'),
                  onPressed: () {
                    Navigator.push<void>(context, MaterialPageRoute<void>(
                      builder: (BuildContext context) {
                        return Scaffold(
                          appBar: AppBar(
                            title: const Text('Page 2'),
                          ),
                        );
                      },
                    ));
                  },
                );
              } ,
            ),
          ),
        ),
      );

      await tester.tap(find.text('Next'));
      await tester.pump();
      await tester.pump(const Duration(milliseconds: 400));

      await tester.pageBack();
      await tester.pump();
      await tester.pump(const Duration(milliseconds: 400));

      expect(find.text('Next'), findsOneWidget);
      expect(find.text('Page 2'), findsNothing);
    });

    testWidgets('successfully taps cupertino back buttons', (WidgetTester tester) async {
      await tester.pumpWidget(
        MaterialApp(
          home: Center(
            child: Builder(
              builder: (BuildContext context) {
                return CupertinoButton(
                  child: const Text('Next'),
                  onPressed: () {
                    Navigator.push<void>(context, CupertinoPageRoute<void>(
                      builder: (BuildContext context) {
                        return CupertinoPageScaffold(
                          navigationBar: const CupertinoNavigationBar(
                            middle: Text('Page 2'),
                          ),
                          child: Container(),
                        );
                      },
                    ));
                  },
                );
              } ,
            ),
          ),
        ),
      );

      await tester.tap(find.text('Next'));
      await tester.pump();
      await tester.pump(const Duration(milliseconds: 400));

      await tester.pageBack();
      await tester.pump();
      await tester.pumpAndSettle();

      expect(find.text('Next'), findsOneWidget);
      expect(find.text('Page 2'), findsNothing);
    });
  });

  testWidgets('hasRunningAnimations control test', (WidgetTester tester) async {
    final AnimationController controller = AnimationController(
      duration: const Duration(seconds: 1),
      vsync: const TestVSync(),
    );
    expect(tester.hasRunningAnimations, isFalse);
    controller.forward();
    expect(tester.hasRunningAnimations, isTrue);
    controller.stop();
    expect(tester.hasRunningAnimations, isFalse);
    controller.forward();
    expect(tester.hasRunningAnimations, isTrue);
    await tester.pumpAndSettle();
    expect(tester.hasRunningAnimations, isFalse);
  });

  testWidgets('pumpAndSettle control test', (WidgetTester tester) async {
    final AnimationController controller = AnimationController(
      duration: const Duration(minutes: 525600),
      vsync: const TestVSync(),
    );
    expect(await tester.pumpAndSettle(), 1);
    controller.forward();
    try {
      await tester.pumpAndSettle();
      expect(true, isFalse);
    } catch (e) {
      expect(e, isFlutterError);
    }
    controller.stop();
    expect(await tester.pumpAndSettle(), 1);
    controller.duration = const Duration(seconds: 1);
    controller.forward();
    expect(await tester.pumpAndSettle(const Duration(milliseconds: 300)), 5); // 0, 300, 600, 900, 1200ms
  });

  testWidgets('Input event array', (WidgetTester tester) async {
      final List<String> logs = <String>[];

      await tester.pumpWidget(
        Directionality(
          textDirection: TextDirection.ltr,
          child: Listener(
            onPointerDown: (PointerDownEvent event) => logs.add('down ${event.buttons}'),
            onPointerMove: (PointerMoveEvent event) => logs.add('move ${event.buttons}'),
            onPointerUp: (PointerUpEvent event) => logs.add('up ${event.buttons}'),
            child: const Text('test'),
          ),
        ),
      );

      final Offset location = tester.getCenter(find.text('test'));
      final List<PointerEventRecord> records = <PointerEventRecord>[
        PointerEventRecord(Duration.zero, <PointerEvent>[
          // Typically PointerAddedEvent is not used in testers, but for records
          // captured on a device it is usually what start a gesture.
          PointerAddedEvent(
            timeStamp: Duration.zero,
            position: location,
          ),
          PointerDownEvent(
            timeStamp: Duration.zero,
            position: location,
            buttons: kSecondaryMouseButton,
            pointer: 1,
          ),
        ]),
        ...<PointerEventRecord>[
          for (Duration t = const Duration(milliseconds: 5);
               t < const Duration(milliseconds: 80);
               t += const Duration(milliseconds: 16))
            PointerEventRecord(t, <PointerEvent>[
              PointerMoveEvent(
                timeStamp: t - const Duration(milliseconds: 1),
                position: location,
                buttons: kSecondaryMouseButton,
                pointer: 1,
              )
            ])
        ],
        PointerEventRecord(const Duration(milliseconds: 80), <PointerEvent>[
          PointerUpEvent(
            timeStamp: const Duration(milliseconds: 79),
            position: location,
            buttons: kSecondaryMouseButton,
            pointer: 1,
          )
        ])
      ];
      final List<Duration> timeDiffs = await tester.handlePointerEventRecord(records);
      expect(timeDiffs.length, records.length);
      for (final Duration diff in timeDiffs) {
        expect(diff, Duration.zero);
      }

      const String b = '$kSecondaryMouseButton';
      expect(logs.first, 'down $b');
      for (int i = 1; i < logs.length - 1; i++) {
        expect(logs[i], 'move $b');
      }
      expect(logs.last, 'up $b');
  });

  group('runAsync', () {
    testWidgets('works with no async calls', (WidgetTester tester) async {
      String? value;
      await tester.runAsync(() async {
        value = '123';
      });
      expect(value, '123');
    });

    testWidgets('works with real async calls', (WidgetTester tester) async {
      final StringBuffer buf = StringBuffer('1');
      await tester.runAsync(() async {
        buf.write('2');
        //ignore: avoid_slow_async_io
        await Directory.current.stat();
        buf.write('3');
      });
      buf.write('4');
      expect(buf.toString(), '1234');
    });

    testWidgets('propagates return values', (WidgetTester tester) async {
      final String? value = await tester.runAsync<String>(() async {
        return '123';
      });
      expect(value, '123');
    });

    testWidgets('reports errors via framework', (WidgetTester tester) async {
      final String? value = await tester.runAsync<String>(() async {
        throw ArgumentError();
      });
      expect(value, isNull);
      expect(tester.takeException(), isArgumentError);
    });

    testWidgets('disallows re-entry', (WidgetTester tester) async {
      final Completer<void> completer = Completer<void>();
      tester.runAsync<void>(() => completer.future);
      expect(() => tester.runAsync(() async { }), throwsA(isA<TestFailure>()));
      completer.complete();
    });

    testWidgets('maintains existing zone values', (WidgetTester tester) async {
      final Object key = Object();
      await runZoned<Future<void>>(() {
        expect(Zone.current[key], 'abczed');
        return tester.runAsync<void>(() async {
          expect(Zone.current[key], 'abczed');
        });
      }, zoneValues: <dynamic, dynamic>{
        key: 'abczed',
      });
    });
  });

  group('showKeyboard', () {
    testWidgets('can be called twice', (WidgetTester tester) async {
      await tester.pumpWidget(
        MaterialApp(
          home: Material(
            child: Center(
              child: TextFormField(),
            ),
          ),
        ),
      );
      await tester.showKeyboard(find.byType(TextField));
      await tester.testTextInput.receiveAction(TextInputAction.done);
      await tester.pump();
      await tester.showKeyboard(find.byType(TextField));
      await tester.testTextInput.receiveAction(TextInputAction.done);
      await tester.pump();
      await tester.showKeyboard(find.byType(TextField));
      await tester.showKeyboard(find.byType(TextField));
      await tester.pump();
    });

    testWidgets(
      'can focus on offstage text input field if finder says not to skip offstage nodes',
      (WidgetTester tester) async {
        await tester.pumpWidget(
          MaterialApp(
            home: Material(
              child: Offstage(
                child: TextFormField(),
              ),
            ),
          ),
        );
        await tester.showKeyboard(find.byType(TextField, skipOffstage: false));
      });
  });

  testWidgets('verifyTickersWereDisposed control test', (WidgetTester tester) async {
    late FlutterError error;
    final Ticker ticker = tester.createTicker((Duration duration) {});
    ticker.start();
    try {
      tester.verifyTickersWereDisposed('');
    } on FlutterError catch (e) {
      error = e;
    } finally {
      expect(error, isNotNull);
      expect(error.diagnostics.length, 4);
      expect(error.diagnostics[2].level, DiagnosticLevel.hint);
      expect(
        error.diagnostics[2].toStringDeep(),
        'Tickers used by AnimationControllers should be disposed by\n'
        'calling dispose() on the AnimationController itself. Otherwise,\n'
        'the ticker will leak.\n',
      );
      expect(error.diagnostics.last, isA<DiagnosticsProperty<Ticker>>());
      expect(error.diagnostics.last.value, ticker);
      expect(error.toStringDeep(), startsWith(
        'FlutterError\n'
        '   A Ticker was active .\n'
        '   All Tickers must be disposed.\n'
        '   Tickers used by AnimationControllers should be disposed by\n'
        '   calling dispose() on the AnimationController itself. Otherwise,\n'
        '   the ticker will leak.\n'
        '   The offending ticker was:\n'
        '     _TestTicker()\n',
      ));
    }
    ticker.stop();
  });

  group('testWidgets variants work', () {
    int numberOfVariationsRun = 0;

    testWidgets('variant tests run all values provided', (WidgetTester tester) async {
      if (debugDefaultTargetPlatformOverride == null) {
        expect(numberOfVariationsRun, equals(TargetPlatform.values.length));
      } else {
        numberOfVariationsRun += 1;
      }
    }, variant: TargetPlatformVariant(TargetPlatform.values.toSet()));

    testWidgets('variant tests have descriptions with details', (WidgetTester tester) async {
      if (debugDefaultTargetPlatformOverride == null) {
        expect(tester.testDescription, equals('variant tests have descriptions with details'));
      } else {
        expect(tester.testDescription, equals('variant tests have descriptions with details ($debugDefaultTargetPlatformOverride)'));
      }
    }, variant: TargetPlatformVariant(TargetPlatform.values.toSet()));
  });

  group('TargetPlatformVariant', () {
    int numberOfVariationsRun = 0;
    TargetPlatform? origTargetPlatform;

    setUpAll((){
      origTargetPlatform = debugDefaultTargetPlatformOverride;
    });

    tearDownAll((){
      expect(debugDefaultTargetPlatformOverride, equals(origTargetPlatform));
    });

    testWidgets('TargetPlatformVariant.only tests given value', (WidgetTester tester) async {
      expect(debugDefaultTargetPlatformOverride, equals(TargetPlatform.iOS));
      expect(defaultTargetPlatform, equals(TargetPlatform.iOS));
    }, variant: TargetPlatformVariant.only(TargetPlatform.iOS));

    testWidgets('TargetPlatformVariant.all tests run all variants', (WidgetTester tester) async {
      if (debugDefaultTargetPlatformOverride == null) {
        expect(numberOfVariationsRun, equals(TargetPlatform.values.length));
      } else {
        numberOfVariationsRun += 1;
      }
    }, variant: TargetPlatformVariant.all());

    testWidgets('TargetPlatformVariant.desktop + mobile contains all TargetPlatform values', (WidgetTester tester) async {
      final TargetPlatformVariant all = TargetPlatformVariant.all();
      final TargetPlatformVariant desktop = TargetPlatformVariant.all();
      final TargetPlatformVariant mobile = TargetPlatformVariant.all();
      expect(desktop.values.union(mobile.values), equals(all.values));
    });
  });

  group('Pending timer', () {
    late TestExceptionReporter currentExceptionReporter;
    setUp(() {
      currentExceptionReporter = reportTestException;
    });

    tearDown(() {
      reportTestException = currentExceptionReporter;
    });

    test('Throws assertion message without code', () async {
      late FlutterErrorDetails flutterErrorDetails;
      reportTestException = (FlutterErrorDetails details, String testDescription) {
        flutterErrorDetails = details;
      };

      final TestWidgetsFlutterBinding binding = TestWidgetsFlutterBinding.ensureInitialized() as TestWidgetsFlutterBinding;
      await binding.runTest(() async {
        final Timer timer = Timer(const Duration(seconds: 1), () {});
        expect(timer.isActive, true);
      }, () {});

      expect(flutterErrorDetails.exception, isA<AssertionError>());
      expect((flutterErrorDetails.exception as AssertionError).message, 'A Timer is still pending even after the widget tree was disposed.');
      expect(binding.inTest, true);
      binding.postTest();
    });
  });
}

class FakeMatcher extends AsyncMatcher {
  FakeMatcher(this.completer);

  final Completer<void> completer;

  @override
  Future<String?> matchAsync(dynamic object) {
    return completer.future.then<String?>((void value) {
      return object?.toString();
    });
  }

  @override
  Description describe(Description description) => description.add('--fake--');
}

class _SingleTickerTest extends StatefulWidget {
  const _SingleTickerTest({Key? key}) : super(key: key);

  @override
  _SingleTickerTestState createState() => _SingleTickerTestState();
}

class _SingleTickerTestState extends State<_SingleTickerTest> with SingleTickerProviderStateMixin {
  late AnimationController controller;

  @override
  void initState() {
    super.initState();
    controller = AnimationController(
      vsync: this,
      duration: const Duration(seconds: 100),
    )  ;
  }

  @override
  Widget build(BuildContext context) {
    return Container();
  }
}

class _AlwaysAnimating extends StatefulWidget {
  const _AlwaysAnimating({
    this.child,
    required this.onPaint,
  });

  final Widget? child;
  final VoidCallback onPaint;

  @override
  State<StatefulWidget> createState() => _AlwaysAnimatingState();
}

class _AlwaysAnimatingState extends State<_AlwaysAnimating> with SingleTickerProviderStateMixin {
  late AnimationController _controller;

  @override
  void initState() {
    super.initState();
    _controller = AnimationController(
      duration: const Duration(milliseconds: 100),
      vsync: this,
    );
    _controller.repeat();
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return AnimatedBuilder(
      animation: _controller.view,
      builder: (BuildContext context, Widget? child) {
        return CustomPaint(
          painter: _AlwaysRepaint(widget.onPaint),
          child: widget.child,
        );
      },
    );
  }
}

class _AlwaysRepaint extends CustomPainter {
  _AlwaysRepaint(this.onPaint);

  final VoidCallback onPaint;

  @override
  bool shouldRepaint(CustomPainter oldDelegate) => true;

  @override
  void paint(Canvas canvas, Size size) {
    onPaint();
  }
}