// Copyright 2014 The Flutter Authors. All rights reserved. // Use of this source code is governed by a BSD-style license that can be // found in the LICENSE file. import 'package:flutter/scheduler.dart'; import 'package:flutter/widgets.dart'; import 'package:flutter_test/flutter_test.dart'; void main() { testWidgets('Does not animate if already at target position', (WidgetTester tester) async { final ScrollController controller = ScrollController(); await tester.pumpWidget( Directionality( textDirection: TextDirection.ltr, child: ListView( controller: controller, children: List<Widget>.generate(80, (int i) => Text('$i', textDirection: TextDirection.ltr)), ), ), ); expectNoAnimation(); final double currentPosition = controller.position.pixels; controller.position.animateTo(currentPosition, duration: const Duration(seconds: 10), curve: Curves.linear); expectNoAnimation(); expect(controller.position.pixels, currentPosition); }); testWidgets('Does not animate if already at target position within tolerance', (WidgetTester tester) async { final ScrollController controller = ScrollController(); await tester.pumpWidget( Directionality( textDirection: TextDirection.ltr, child: ListView( controller: controller, children: List<Widget>.generate(80, (int i) => Text('$i', textDirection: TextDirection.ltr)), ), ), ); expectNoAnimation(); final double halfTolerance = controller.position.physics.tolerance.distance / 2; expect(halfTolerance, isNonZero); final double targetPosition = controller.position.pixels + halfTolerance; controller.position.animateTo(targetPosition, duration: const Duration(seconds: 10), curve: Curves.linear); expectNoAnimation(); expect(controller.position.pixels, targetPosition); }); testWidgets('Animates if going to a position outside of tolerance', (WidgetTester tester) async { final ScrollController controller = ScrollController(); await tester.pumpWidget( Directionality( textDirection: TextDirection.ltr, child: ListView( controller: controller, children: List<Widget>.generate(80, (int i) => Text('$i', textDirection: TextDirection.ltr)), ), ), ); expectNoAnimation(); final double doubleTolerance = controller.position.physics.tolerance.distance * 2; expect(doubleTolerance, isNonZero); final double targetPosition = controller.position.pixels + doubleTolerance; controller.position.animateTo(targetPosition, duration: const Duration(seconds: 10), curve: Curves.linear); expect(SchedulerBinding.instance.transientCallbackCount, equals(1), reason: 'Expected an animation.'); }); } void expectNoAnimation() { expect(SchedulerBinding.instance.transientCallbackCount, equals(0), reason: 'Expected no animation.'); }