Flutter 如何测试小部件在'；它最初位于视口之外

我有一个自定义小部件组件：

class CollectAssetDataButton extends StatelessWidget {
  const CollectAssetDataButton({ Key key }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return RaisedButton(
        child: Text(
      context
          .translate(I18NKeys.appointmentDetails.collectAssetsData)
          .toUpperCase(),
    ),
    onPressed: () {},
  );
  }
}

我正在尝试使用以下方法进行测试：

  final collectAssetsButtonFinder = find.byKey(WidgetKeysAppointmentDetails.collectAssetsButton);
  expect(collectAssetsButtonFinder, findsOneWidget);

根据中的建议

但我仍然得到：

══╡ EXCEPTION CAUGHT BY FLUTTER TEST FRAMEWORK ╞════════════════════════════════════════════════════
The following TestFailure object was thrown running a test:
  Expected: exactly one matching node in the widget tree
  Actual: _KeyFinder:<zero widgets with key [<'___appointment_details_collect_assets_button___'>]
(ignoring offstage widgets)>
   Which: means none were found but one was expected

══╡ 颤振测试框架捕获异常╞════════════════════════════════════════════════════
运行测试时引发了以下TestFailure对象：
预期：小部件树中只有一个匹配节点
实际：_KeyFinder:
这意味着除了预期的一个之外，没有找到任何对象

提前谢谢