单元测试 -> 无法在此 ChangeNotifierProvider<Counter> 小部件上方找到正确的 Provider<Counter>

Question

我想ChangeNotifierProvider在我的项目中为 Provider ( )创建一个单元测试，我的单元测试、小部件测试和集成测试成功通过了??，所以现在我尝试（努力......）为提供者创建一个单元测试。我能够检查上下文，但是在检查提供程序的初始值（必须为 0）时，出现此异常？：

??? EXCEPTION CAUGHT BY FLUTTER TEST FRAMEWORK ?????????????????????????????????????????????????????
The following ProviderNotFoundError was thrown running a test:
Error: Could not find the correct Provider<Counter> above this ChangeNotifierProvider<Counter>
Widget

To fix, please:

  * Ensure the Provider<Counter> is an ancestor to this ChangeNotifierProvider<Counter> Widget
  * Provide types to Provider<Counter>
  * Provide types to Consumer<Counter>
  * Provide types to Provider.of<Counter>()
  * Always use package imports. Ex: `import 'package:my_app/my_code.dart';
  * Ensure the correct `context` is being used.

If none of these solutions work, please file a bug at:
https://github.com/rrousselGit/provider/issues

When the exception was thrown, this was the stack:
#0      Provider.of (package:provider/src/provider.dart:264:7)
#1      main.<anonymous closure>.<anonymous closure> (file:///home/chinnonsantos/FlutterProjects/full_testing_flutter/test/unit/provider_test.dart:33:23)
<asynchronous suspension>
#2      testWidgets.<anonymous closure>.<anonymous closure> (package:flutter_test/src/widget_tester.dart:119:25)
<asynchronous suspension>
#3      TestWidgetsFlutterBinding._runTestBody (package:flutter_test/src/binding.dart:648:19)
<asynchronous suspension>
#6      TestWidgetsFlutterBinding._runTest (package:flutter_test/src/binding.dart:631:14)
#7      AutomatedTestWidgetsFlutterBinding.runTest.<anonymous closure> (package:flutter_test/src/binding.dart:1016:24)
#13     AutomatedTestWidgetsFlutterBinding.runTest (package:flutter_test/src/binding.dart:1013:15)
#14     testWidgets.<anonymous closure> (package:flutter_test/src/widget_tester.dart:116:22)
#15     Declarer.test.<anonymous closure>.<anonymous closure>.<anonymous closure> (package:test_api/src/backend/declarer.dart:168:27)
<asynchronous suspension>
#16     Invoker.waitForOutstandingCallbacks.<anonymous closure> (package:test_api/src/backend/invoker.dart:250:15)
<asynchronous suspension>
#21     Invoker.waitForOutstandingCallbacks (package:test_api/src/backend/invoker.dart:247:5)
#22     Declarer.test.<anonymous closure>.<anonymous closure> (package:test_api/src/backend/declarer.dart:166:33)
#27     Declarer.test.<anonymous closure> (package:test_api/src/backend/declarer.dart:165:13)
<asynchronous suspension>
#28     Invoker._onRun.<anonymous closure>.<anonymous closure>.<anonymous closure>.<anonymous closure> (package:test_api/src/backend/invoker.dart:400:25)
<asynchronous suspension>
#42     _Timer._runTimers (dart:isolate-patch/timer_impl.dart:382:19)
#43     _Timer._handleMessage (dart:isolate-patch/timer_impl.dart:416:5)
#44     _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:172:12)
(elided 28 frames from class _FakeAsync, package dart:async, package dart:async-patch, and package stack_trace)

The test description was:
  Update when the value changes
????????????????????????????????????????????????????????????????????????????????????????????????????
00:03 +0 -1: [Provider] Update when the value changes [E]                                                               
  Test failed. See exception logs above.
  The test description was: Update when the value changes

00:03 +0 -1: Some tests failed.                                                                                         
Collecting coverage information...

按照我的代码： - pubspec.yaml：

...
dependencies:
  flutter:
    sdk: flutter
  test: ^1.6.3
  provider: ^3.2.0

dev_dependencies:
  flutter_test:
    sdk: flutter
  flutter_driver:
    sdk: flutter
  pedantic: ^1.8.0+1
...

• lib/main.dart：

...
dependencies:
  flutter:
    sdk: flutter
  test: ^1.6.3
  provider: ^3.2.0

dev_dependencies:
  flutter_test:
    sdk: flutter
  flutter_driver:
    sdk: flutter
  pedantic: ^1.8.0+1
...

• lib/counter.dart：

import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'package:full_testing_flutter/counter.dart';

void main() {
  runApp(
    ChangeNotifierProvider(
      create: (context) => Counter(),
      child: MyApp(),
    ),
  );
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatelessWidget {
  final String title;

  MyHomePage({this.title});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Consumer<Counter>(
              builder: (context, counter, child) => Text(
                '${counter.value}',
                key: Key('counter'),
                style: Theme.of(context).textTheme.display1,
              ),
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        key: Key('increment'),
        onPressed: () =>
            Provider.of<Counter>(context, listen: false).increment(),
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
}

• test/unit/provider_test.dart：

import 'package:flutter/foundation.dart';

class Counter with ChangeNotifier {
  int value = 0;

  void increment() {
    value++;
    // print('Value++: $value');
    notifyListeners();
  }

  void decrement() {
    value--;
    // print('Value--: $value');
    notifyListeners();
  }
}

• test/unit/counter_test.dart，test/widget/widget_test.dart和test_driver/app_test.dart：

  现在不重要，但如果你想看，可以在full_testing_flutter（公共项目）存储库中找到

我可以做什么来测试提供者（隔离）？我的代码中的错误在哪里？

我从 Dart/Flutter 开始，尤其是 Provider 包，有人可以帮助我吗？

注意：我的应用程序运行良好，只有我对提供者的单元测试（我现在正在实施的）不起作用！！！

谢谢

Answer 1

This problem happens because you are using the BuildContext of the provider you want to obtain to call Provider.of:

Provider<T>(
  key: myKey,
  ...
)


Provider.of<T>(myKey.currentContext);

This is not possible, and only the descendants of the said provider can call Provider.of.

Consider changing your test to something like:

testWidget('Provider.of', (tester) async {
  await tester.pumpWidget(
    Provider(
      create: (_) => 42,
      child: Container(),
    ),
  );

  final context = tester.element(find.byType(Container));

  expect(Provider.of<int>(context), equals(42));
});