如何在颤动中测试状态？

Question

所以我有一个简单的计数器应用程序，

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

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

class _CounterAppState extends State<CounterApp> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Text(_counter.toString()),
      ),
    );
  }
}

那么如何测试 _counter 状态？

我试过这样做，

testWidgets("counter", (tester) async {
  const key = Key("counter");
  await tester.pumpWidget(const CounterApp(key: key));

  final state = tester.state(find.byKey(key));

  expect(state._counter, 0);
});

但是我收到错误 Error: The getter '_counter' isn't defined for the class。我们甚至应该测试状态吗？

Answer 1

首先在使用state方法时需要指定类型，以免编译出错：

final _CounterAppState state = tester.state(find.byKey(key));

其次，_CounterAppState 和 _counter 是私有的，您不应该直接测试私有 classes/variables。您可以制作 class public 并为私有变量提供 public getter：

int get testCounter => _counter;

但是，有一种访问私有声明的方法我不推荐。用 @visibleForTesting 注释你的私人 variable/class 将使它 public 使代码可测试。不要忘记导入基础库或元库。

visibleForTesting top-level constant

Used to annotate a declaration that was made public, so that it is more visible than otherwise necessary, to make code testable.

Tools, such as the analyzer, can provide feedback if

the annotation is associated with a declaration not in the lib folder of a package, or a private declaration, or a declaration in an unnamed static extension, or

the declaration is referenced outside of its defining library or a library which is in the test folder of the defining package.

实现如下：

// Import the foundation library
import 'package:flutter/foundation.dart';

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

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

// Add the annotation above the class
@visibleForTesting
class _CounterAppState extends State<CounterApp> {
  // Add the annotation above the variable
  @visibleForTesting
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Text(_counter.toString()),
      ),
    );
  }
}

您可能希望在测试后删除注释。

如何在颤动中测试状态？

How to test state in flutter?

flutter

flutter-test

visibleForTesting top-level constant