在Image小部件上测试GestureDetector

Question

我已经创建了一个简单的测试用例应用程序,您单击一个小部件,使用GestureDetector该小部件触发setState对tapCount变量的更新.

应用程序在模拟器中正常工作,如上所示正确更新文本,但是一旦我尝试Flutter小部件测试,小部件测试就会失败,因为文本在测试环境中没有正确更新.

可重复的例子:

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatefulWidget {
  MyApp();

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

class _MyAppState extends State<MyApp> {
  int tapCount = 0;

  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: SafeArea(
          child: Column(
            children: <Widget>[
              MyImage(
                onTap: () {
                  setState(() {
                    tapCount += 1;
                  });
                },
                imagePath: 'assets/my-image.jpg',
              ),
              Text(tapCount.toString())
            ],
          ),
        ),
      ),
    );
  }
}

class MyImage extends StatelessWidget {
  final Function() onTap;
  final String imagePath;

  const MyImage({
    Key key,
    @required this.onTap,
    @required this.imagePath,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onTap: () {
        this.onTap();
      },
      child: Image.asset(
        imagePath,
        height: 100.0,
      ),
    );
  }
}

在pubspec中,我下载了一个随机图像并验证了图像是否在模拟器中成功显示.

  assets:
    - assets/my-image.jpg

我的测试与添加await tester.pumpAndSettle();和点击图像的样本相同:

void main() {
  testWidgets('Counter increments smoke test', (WidgetTester tester) async {
    // Build our app and trigger a frame.
    await tester.pumpWidget(MyApp());
    await tester.pumpAndSettle();

    // Verify that our counter starts at 0.
    expect(find.text('0'), findsOneWidget);
    expect(find.text('1'), findsNothing);

    // Tap the image and trigger a frame.
    await tester.tap(find.byType(MyImage));
    await tester.pump();
    await tester.pumpAndSettle();

    // Verify that our counter has incremented.
    expect(find.text('0'), findsNothing); // this test fails
    expect(find.text('1'), findsOneWidget); // this test fails
  });
}

当我运行测试时,我收到此错误

??? EXCEPTION CAUGHT BY FLUTTER TEST FRAMEWORK ?????????????????????????????????????????????????????
The following TestFailure object was thrown running a test:
  Expected: no matching nodes in the widget tree
  Actual: ?:<exactly one widget with text "0" (ignoring offstage widgets): Text("0")>
   Which: means one was found but none were expected

When the exception was thrown, this was the stack:
#4      main.<anonymous closure> (file:///Projects/untitled/test/widget_test.dart:27:5)
<asynchronous suspension>
#5      testWidgets.<anonymous closure>.<anonymous closure> (package:flutter_test/src/widget_tester.dart:82:23)
#6      TestWidgetsFlutterBinding._runTestBody (package:flutter_test/src/binding.dart:566:19)
<asynchronous suspension>
#9      TestWidgetsFlutterBinding._runTest (package:flutter_test/src/binding.dart:550:14)
#10     AutomatedTestWidgetsFlutterBinding.runTest.<anonymous closure> (package:flutter_test/src/binding.dart:893:24)
#16     AutomatedTestWidgetsFlutterBinding.runTest (package:flutter_test/src/binding.dart:890:15)
#17     testWidgets.<anonymous closure> (package:flutter_test/src/widget_tester.dart:81:22)
#18     Declarer.test.<anonymous closure>.<anonymous closure>.<anonymous closure> (package:test_api/src/backend/declarer.dart:168:27)
<asynchronous suspension>
#19     Invoker.waitForOutstandingCallbacks.<anonymous closure> (package:test_api/src/backend/invoker.dart:249:15)
<asynchronous suspension>
#24     Invoker.waitForOutstandingCallbacks (package:test_api/src/backend/invoker.dart:246:5)
#25     Declarer.test.<anonymous closure>.<anonymous closure> (package:test_api/src/backend/declarer.dart:166:33)
#30     Declarer.test.<anonymous closure> (package:test_api/src/backend/declarer.dart:165:13)
<asynchronous suspension>
#31     Invoker._onRun.<anonymous closure>.<anonymous closure>.<anonymous closure>.<anonymous closure> (package:test_api/src/backend/invoker.dart:399:25)
<asynchronous suspension>
#45     _Timer._runTimers (dart:isolate/runtime/libtimer_impl.dart:382:19)
#46     _Timer._handleMessage (dart:isolate/runtime/libtimer_impl.dart:416:5)
#47     _RawReceivePortImpl._handleMessage (dart:isolate/runtime/libisolate_patch.dart:171:12)
(elided 28 frames from class _FakeAsync, package dart:async, and package stack_trace)

This was caught by the test expectation on the following line:
  file:///Projects/untitled/test/widget_test.dart line 27

The test description was:
Counter increments smoke test
????????????????????????????????????????????????????????????????????????????????????????????????????

Test failed. See exception logs above.
The test description was: Counter increments smoke test

如果我尝试相同的测试,但Image内部MyImage用另一个小部件(例如另一个Text小部件)替换main.dart,测试通过:

class MyImage extends StatelessWidget {
  final Function() onTap;
  final String imagePath;

  const MyImage({
    Key key,
    @required this.onTap,
    @required this.imagePath,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onTap: () {
        this.onTap();
      },
      child: Text( // replaced Image with Text and test passes!
        imagePath,
      ),
    );
  }
}

这让我觉得问题是由于使用了Image,但我无法弄清楚原因.

如果您想尝试测试,代码也会上传到GitHub上.

Answer 1

这是我对为什么它不能处理图像的看法。抖动测试在FakeAsync区域中运行，并且当您需要运行真正的异步代码（例如通过assetBundle加载资产）时，资产未加载且图像小部件的大小保持为零，因此命中测试失败。如果您事先设置图像的高度和宽度，则测试通过。