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appBar: AppBar(
title: const text(title),
),
body: ListView.builder(
// add a key to the ListView. this makes it possible to
// find the list and scroll through it in the tests.
key: const key('long_list'),
itemCount: items.length,
itemBuilder: (context, index) {
return ListTile(
title: text(
items[index],
// add a key to the text widget for each item. this makes
// it possible to look for a particular item in the list
// and verify that the text is correct
key: key('item_${index}_text'),
),
);
},
),
),
);
}
}
<code_end>
<topic_end>
<topic_start>
2. write a test that scrolls through the list
now, you can write a test. in this example, scroll through the list of items and
verify that a particular item exists in the list. the WidgetTester class
provides the scrollUntilVisible() method, which scrolls through a list
until a specific widget is visible. this is useful because the height of the
items in the list can change depending on the device.
rather than assuming that you know the height of all the items
in a list, or that a particular widget is rendered on all devices,
the scrollUntilVisible() method repeatedly scrolls through
a list of items until it finds what it’s looking for.
the following code shows how to use the scrollUntilVisible() method
to look through the list for a particular item. this code lives in a
file called test/widget_test.dart.
<code_start>
// this is a basic flutter widget test.
//
// to perform an interaction with a widget in your test, use the WidgetTester
// utility that flutter provides. for example, you can send tap and scroll
// gestures. you can also use WidgetTester to find child widgets in the widget
// tree, read text, and verify that the values of widget properties are correct.
import 'package:flutter/material.dart';
import 'package:flutter_test/flutter_test.dart';
import 'package:scrolling/main.dart';
void main() {
testWidgets('finds a deep item in a long list', (tester) async {
// build our app and trigger a frame.
await tester.pumpWidget(MyApp(
items: List<String>.generate(10000, (i) => 'item $i'),
));
final listFinder = find.byType(Scrollable);
final itemFinder = find.byKey(const ValueKey('item_50_text'));
// scroll until the item to be found appears.
await tester.scrollUntilVisible(
itemFinder,
500.0,
scrollable: listFinder,
);
// verify that the item contains the correct text.
expect(itemFinder, findsOneWidget);
});
}
<code_end>
<topic_end>
<topic_start>
3. run the test
run the test using the following command from the root of the project:
<topic_end>
<topic_start>
tap, drag, and enter text
many widgets not only display information, but also respond
to user interaction. this includes buttons that can be tapped,
and TextField for entering text.
to test these interactions, you need a way to simulate them
in the test environment. for this purpose, use the
WidgetTester library.
the WidgetTester provides methods for entering text,
tapping, and dragging.
in many cases, user interactions update the state of the app. in the test
environment, flutter doesn’t automatically rebuild widgets when the state
changes. to ensure that the widget tree is rebuilt after simulating a user
interaction, call the pump() or pumpAndSettle()
methods provided by the WidgetTester.
this recipe uses the following steps:
<topic_end>
<topic_start>
1. create a widget to test
for this example,
create a basic todo app that tests three features:
to keep the focus on testing,
this recipe won’t provide a detailed guide on how to build the todo app.
to learn more about how this app is built,
see the relevant recipes:
<code_start>