packages/flutter/test/rendering/sliver_cache_test.dart

// Copyright 2018 The Chromium 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/foundation.dart';
import 'package:flutter/rendering.dart';
import 'package:test/test.dart';

import 'rendering_tester.dart';

void main() {
  test('RenderViewport calculates correct constraints, RenderSliverToBoxAdapter calculates correct geometry', () {
    final List<RenderSliver> children = new List<RenderSliver>.generate(30, (int index) {
      return new RenderSliverToBoxAdapter(
        child: new RenderSizedBox(const Size(400.0, 100.0)),
      );
    });

    // Viewport is 800x600, can show 6 children at a time.

    final RenderViewport root = new RenderViewport(
      axisDirection: AxisDirection.down,
      crossAxisDirection: AxisDirection.right,
      offset: new ViewportOffset.zero(),
      cacheExtent: 250.0,
      children: children,
    );
    layout(root);

    RenderSliver firstVisible = children[0];
    expectSliverConstraints(
      sliver: firstVisible,
      cacheOrigin: 0.0,
      remainingPaintExtent: 600.0,
      remainingCacheExtent: 600.0 + 250.0,
      scrollOffset: 0.0,
    );
    expectSliverGeometry(
      sliver: firstVisible,
      paintExtent: 100.0,
      cacheExtent: 100.0,
      visible: true,
    );

    RenderSliver lastVisible = children[5];
    expectSliverConstraints(
      sliver: lastVisible,
      cacheOrigin: 0.0,
      remainingPaintExtent: 100.0,
      remainingCacheExtent: 350.0,
      scrollOffset: 0.0,
    );
    expectSliverGeometry(
      sliver: lastVisible,
      paintExtent: 100.0,
      cacheExtent: 100.0,
      visible: true,
    );

    RenderSliver firstInCache = children[6];
    expectSliverConstraints(
      sliver: firstInCache,
      cacheOrigin: 0.0,
      remainingPaintExtent: 0.0,
      remainingCacheExtent: 250.0,
      scrollOffset: 0.0,
    );
    expectSliverGeometry(
      sliver: firstInCache,
      paintExtent: 0.0,
      cacheExtent: 100.0,
      visible: false,
    );

    RenderSliver lastInCache = children[8];
    expectSliverConstraints(
      sliver: lastInCache,
      cacheOrigin: 0.0,
      remainingPaintExtent: 0.0,
      remainingCacheExtent: 50.0,
      scrollOffset: 0.0,
    );
    expectSliverGeometry(
      sliver: lastInCache,
      paintExtent: 0.0,
      cacheExtent: 50.0,
      visible: false,
    );

    RenderSliver outsideCache = children[9];
    expectSliverConstraints(
      sliver: outsideCache,
      cacheOrigin: 0.0,
      remainingPaintExtent: 0.0,
      remainingCacheExtent: 0.0,
      scrollOffset: 0.0,
    );
    expectSliverGeometry(
      sliver: outsideCache,
      paintExtent: 0.0,
      cacheExtent: 0.0,
      visible: false,
    );

    // scroll down half a sliver
    root.offset = new ViewportOffset.fixed(50.0);
    pumpFrame();

    firstVisible = children[0];
    expectSliverConstraints(
      sliver: firstVisible,
      cacheOrigin: -50.0,
      remainingPaintExtent: 600.0,
      remainingCacheExtent: 50.0 + 600.0 + 250.0,
      scrollOffset: 50.0,
    );
    expectSliverGeometry(
      sliver: firstVisible,
      paintExtent: 50.0,
      cacheExtent: 100.0,
      visible: true,
    );

    lastVisible = children[6];
    expectSliverConstraints(
      sliver: lastVisible,
      cacheOrigin: 0.0,
      remainingPaintExtent: 50.0,
      remainingCacheExtent: 300.0,
      scrollOffset: 0.0,
    );
    expectSliverGeometry(
      sliver: lastVisible,
      paintExtent: 50.0,
      cacheExtent: 100.0,
      visible: true,
    );

    firstInCache = children[7];
    expectSliverConstraints(
      sliver: firstInCache,
      cacheOrigin: 0.0,
      remainingPaintExtent: 0.0,
      remainingCacheExtent: 200.0,
      scrollOffset: 0.0,
    );
    expectSliverGeometry(
      sliver: firstInCache,
      paintExtent: 0.0,
      cacheExtent: 100.0,
      visible: false,
    );

    lastInCache = children[8];
    expectSliverConstraints(
      sliver: lastInCache,
      cacheOrigin: 0.0,
      remainingPaintExtent: 0.0,
      remainingCacheExtent: 100.0,
      scrollOffset: 0.0,
    );
    expectSliverGeometry(
      sliver: lastInCache,
      paintExtent: 0.0,
      cacheExtent: 100.0,
      visible: false,
    );

    outsideCache = children[9];
    expectSliverConstraints(
      sliver: outsideCache,
      cacheOrigin: 0.0,
      remainingPaintExtent: 0.0,
      remainingCacheExtent: 0.0,
      scrollOffset: 0.0,
    );
    expectSliverGeometry(
      sliver: outsideCache,
      paintExtent: 0.0,
      cacheExtent: 0.0,
      visible: false,
    );

    // scroll down 1.5 slivers
    root.offset = new ViewportOffset.fixed(150.0);
    pumpFrame();

    RenderSliver firstInPreCache = children[0];
    expectSliverConstraints(
      sliver: firstInPreCache,
      cacheOrigin: -150.0,
      remainingPaintExtent: 600.0,
      remainingCacheExtent: 150.0 + 600.0 + 250.0,
      scrollOffset: 150.0,
    );
    expectSliverGeometry(
      sliver: firstInPreCache,
      paintExtent: 0.0,
      cacheExtent: 100.0,
      visible: false,
    );

    firstVisible = children[1];
    expectSliverConstraints(
      sliver: firstVisible,
      cacheOrigin: -50.0,
      remainingPaintExtent: 600.0,
      remainingCacheExtent: 50.0 + 600.0 + 250.0,
      scrollOffset: 50.0,
    );
    expectSliverGeometry(
      sliver: firstVisible,
      paintExtent: 50.0,
      cacheExtent: 100.0,
      visible: true,
    );

    // scroll down 10 slivers
    root.offset = new ViewportOffset.fixed(1000.0);
    pumpFrame();

    final RenderSliver first = children[0];
    expectSliverConstraints(
      sliver: first,
      cacheOrigin: -250.0,
      remainingPaintExtent: 600.0,
      remainingCacheExtent: 250.0 + 600.0 + 250.0,
      scrollOffset: 1000.0,
    );
    expectSliverGeometry(
      sliver: first,
      paintExtent: 0.0,
      cacheExtent: 0.0,
      visible: false,
    );

    firstInPreCache = children[7];
    expectSliverConstraints(
      sliver: firstInPreCache,
      cacheOrigin: -250.0,
      remainingPaintExtent: 600.0,
      remainingCacheExtent: 250.0 + 600.0 + 250.0,
      scrollOffset: 300.0,
    );
    expectSliverGeometry(
      sliver: firstInPreCache,
      paintExtent: 0.0,
      cacheExtent: 50.0,
      visible: false,
    );

    final RenderSliver lastInPreCache = children[9];
    expectSliverConstraints(
      sliver: lastInPreCache,
      cacheOrigin: -100.0,
      remainingPaintExtent: 600.0,
      remainingCacheExtent: 100.0 + 600.0 + 250.0,
      scrollOffset: 100.0,
    );
    expectSliverGeometry(
      sliver: lastInPreCache,
      paintExtent: 0.0,
      cacheExtent: 100.0,
      visible: false,
    );

    firstVisible = children[10];
    expectSliverConstraints(
      sliver: firstVisible,
      cacheOrigin: 0.0,
      remainingPaintExtent: 600.0,
      remainingCacheExtent: 600.0 + 250.0,
      scrollOffset: 0.0,
    );
    expectSliverGeometry(
      sliver: firstVisible,
      paintExtent: 100.0,
      cacheExtent: 100.0,
      visible: true,
    );
  });

  test('RenderSliverFixedExtentList calculates correct geometry', () {
    // Viewport is 800x600, can show 6 full children at a time
    final List<RenderBox> children = new List<RenderBox>.generate(30, (int index) {
      return new RenderSizedBox(const Size(400.0, 100.0));
    });
    final TestRenderSliverBoxChildManager childManager = new TestRenderSliverBoxChildManager(
      children: children,
    );
    RenderSliverFixedExtentList inner;
    final RenderViewport root = new RenderViewport(
      axisDirection: AxisDirection.down,
      crossAxisDirection: AxisDirection.right,
      offset: new ViewportOffset.zero(),
      cacheExtent: 250.0,
      children: <RenderSliver>[
        inner = childManager.createRenderSliverFixedExtentList(),
      ],
    );
    layout(root);

    expectSliverConstraints(
      sliver: inner,
      cacheOrigin: 0.0,
      remainingPaintExtent: 600.0,
      remainingCacheExtent: 600.0 + 250.0,
      scrollOffset: 0.0,
    );
    expectSliverGeometry(
      sliver: inner,
      paintExtent: 600.0,
      cacheExtent: 850.0,
      visible: true,
    );
    expect(children.sublist(0, 9).every((RenderBox r) => r.attached), true);
    expect(children.sublist(9, 30).any((RenderBox r) => r.attached), false);

    // scroll half an item down
    root.offset = new ViewportOffset.fixed(50.0);
    pumpFrame();

    expectSliverConstraints(
      sliver: inner,
      cacheOrigin: -50.0,
      remainingPaintExtent: 600.0,
      remainingCacheExtent: 50.0 + 600.0 + 250.0,
      scrollOffset: 50.0,
    );
    expectSliverGeometry(
      sliver: inner,
      paintExtent: 600.0,
      cacheExtent: 900.0,
      visible: true,
    );
    expect(children.sublist(0, 9).every((RenderBox r) => r.attached), true);
    expect(children.sublist(9, 30).any((RenderBox r) => r.attached), false);


    // scroll to the middle
    root.offset = new ViewportOffset.fixed(1500.0);
    pumpFrame();

    expectSliverConstraints(
      sliver: inner,
      cacheOrigin: -250.0,
      remainingPaintExtent: 600.0,
      remainingCacheExtent: 250.0 + 600.0 + 250.0,
      scrollOffset: 1500.0,
    );
    expectSliverGeometry(
      sliver: inner,
      paintExtent: 600.0,
      cacheExtent: 1100.0,
      visible: true,
    );

    expect(children.sublist(0, 12).any((RenderBox r) => r.attached), false);
    expect(children.sublist(12, 24).every((RenderBox r) => r.attached), true);
    expect(children.sublist(24, 30).any((RenderBox r) => r.attached), false);

    // scroll to the end
    root.offset = new ViewportOffset.fixed(2400.0);
    pumpFrame();

    expectSliverConstraints(
      sliver: inner,
      cacheOrigin: -250.0,
      remainingPaintExtent: 600.0,
      remainingCacheExtent: 250.0 + 600.0 + 250.0,
      scrollOffset: 2400.0,
    );
    expectSliverGeometry(
      sliver: inner,
      paintExtent: 600.0,
      cacheExtent: 850.0,
      visible: true,
    );
    expect(children.sublist(0, 21).any((RenderBox r) => r.attached), false);
    expect(children.sublist(21, 30).every((RenderBox r) => r.attached), true);
  });

  test('RenderSliverList calculates correct geometry', () {
    // Viewport is 800x600, can show 6 full children at a time
    final List<RenderBox> children = new List<RenderBox>.generate(30, (int index) {
      return new RenderSizedBox(const Size(400.0, 100.0));
    });
    final TestRenderSliverBoxChildManager childManager = new TestRenderSliverBoxChildManager(
      children: children,
    );
    RenderSliverList inner;
    final RenderViewport root = new RenderViewport(
      axisDirection: AxisDirection.down,
      crossAxisDirection: AxisDirection.right,
      offset: new ViewportOffset.zero(),
      cacheExtent: 250.0,
      children: <RenderSliver>[
        inner = childManager.createRenderSliverList(),
      ],
    );
    layout(root);

    expectSliverConstraints(
      sliver: inner,
      cacheOrigin: 0.0,
      remainingPaintExtent: 600.0,
      remainingCacheExtent: 600.0 + 250.0,
      scrollOffset: 0.0,
    );
    expectSliverGeometry(
      sliver: inner,
      paintExtent: 600.0,
      cacheExtent: 850.0,
      visible: true,
    );
    expect(children.sublist(0, 9).every((RenderBox r) => r.attached), true);
    expect(children.sublist(9, 30).any((RenderBox r) => r.attached), false);

    // scroll half an item down
    root.offset = new ViewportOffset.fixed(50.0);
    pumpFrame();

    expectSliverConstraints(
      sliver: inner,
      cacheOrigin: -50.0,
      remainingPaintExtent: 600.0,
      remainingCacheExtent: 50.0 + 600.0 + 250.0,
      scrollOffset: 50.0,
    );
    expectSliverGeometry(
      sliver: inner,
      paintExtent: 600.0,
      cacheExtent: 900.0,
      visible: true,
    );
    expect(children.sublist(0, 9).every((RenderBox r) => r.attached), true);
    expect(children.sublist(9, 30).any((RenderBox r) => r.attached), false);


    // scroll to the middle
    root.offset = new ViewportOffset.fixed(1500.0);
    pumpFrame();

    expectSliverConstraints(
      sliver: inner,
      cacheOrigin: -250.0,
      remainingPaintExtent: 600.0,
      remainingCacheExtent: 250.0 + 600.0 + 250.0,
      scrollOffset: 1500.0,
    );
    expectSliverGeometry(
      sliver: inner,
      paintExtent: 600.0,
      cacheExtent: 1100.0,
      visible: true,
    );

    expect(children.sublist(0, 12).any((RenderBox r) => r.attached), false);
    expect(children.sublist(12, 24).every((RenderBox r) => r.attached), true);
    expect(children.sublist(24, 30).any((RenderBox r) => r.attached), false);

    // scroll to the end
    root.offset = new ViewportOffset.fixed(2400.0);
    pumpFrame();

    expectSliverConstraints(
      sliver: inner,
      cacheOrigin: -250.0,
      remainingPaintExtent: 600.0,
      remainingCacheExtent: 250.0 + 600.0 + 250.0,
      scrollOffset: 2400.0,
    );
    expectSliverGeometry(
      sliver: inner,
      paintExtent: 600.0,
      cacheExtent: 850.0,
      visible: true,
    );
    expect(children.sublist(0, 21).any((RenderBox r) => r.attached), false);
    expect(children.sublist(21, 30).every((RenderBox r) => r.attached), true);
  });

  test('RenderSliverGrid calculates correct geometry', () {
    // Viewport is 800x600, each grid element is 400x100, giving us space for 12 visible children
    final List<RenderBox> children = new List<RenderBox>.generate(60, (int index) {
      return new RenderSizedBox(const Size(400.0, 100.0));
    });
    final TestRenderSliverBoxChildManager childManager = new TestRenderSliverBoxChildManager(
      children: children,
    );
    RenderSliverGrid inner;
    final RenderViewport root = new RenderViewport(
      axisDirection: AxisDirection.down,
      crossAxisDirection: AxisDirection.right,
      offset: new ViewportOffset.zero(),
      cacheExtent: 250.0,
      children: <RenderSliver>[
        inner = childManager.createRenderSliverGrid(),
      ],
    );
    layout(root);

    expectSliverConstraints(
      sliver: inner,
      cacheOrigin: 0.0,
      remainingPaintExtent: 600.0,
      remainingCacheExtent: 600.0 + 250.0,
      scrollOffset: 0.0,
    );
    expectSliverGeometry(
      sliver: inner,
      paintExtent: 600.0,
      cacheExtent: 850.0,
      visible: true,
    );
    expect(children.sublist(0, 18).every((RenderBox r) => r.attached), true);
    expect(children.sublist(18, 60).any((RenderBox r) => r.attached), false);

    // scroll half an item down
    root.offset = new ViewportOffset.fixed(50.0);
    pumpFrame();

    expectSliverConstraints(
      sliver: inner,
      cacheOrigin: -50.0,
      remainingPaintExtent: 600.0,
      remainingCacheExtent: 50.0 + 600.0 + 250.0,
      scrollOffset: 50.0,
    );
    expectSliverGeometry(
      sliver: inner,
      paintExtent: 600.0,
      cacheExtent: 900.0,
      visible: true,
    );
    expect(children.sublist(0, 18).every((RenderBox r) => r.attached), true);
    expect(children.sublist(18, 60).any((RenderBox r) => r.attached), false);


    // scroll to the middle
    root.offset = new ViewportOffset.fixed(1500.0);
    pumpFrame();

    expectSliverConstraints(
      sliver: inner,
      cacheOrigin: -250.0,
      remainingPaintExtent: 600.0,
      remainingCacheExtent: 250.0 + 600.0 + 250.0,
      scrollOffset: 1500.0,
    );
    expectSliverGeometry(
      sliver: inner,
      paintExtent: 600.0,
      cacheExtent: 1100.0,
      visible: true,
    );

    expect(children.sublist(0, 24).any((RenderBox r) => r.attached), false);
    expect(children.sublist(24, 48).every((RenderBox r) => r.attached), true);
    expect(children.sublist(48, 60).any((RenderBox r) => r.attached), false);

    // scroll to the end
    root.offset = new ViewportOffset.fixed(2400.0);
    pumpFrame();

    expectSliverConstraints(
      sliver: inner,
      cacheOrigin: -250.0,
      remainingPaintExtent: 600.0,
      remainingCacheExtent: 250.0 + 600.0 + 250.0,
      scrollOffset: 2400.0,
    );
    expectSliverGeometry(
      sliver: inner,
      paintExtent: 600.0,
      cacheExtent: 850.0,
      visible: true,
    );
    expect(children.sublist(0, 42).any((RenderBox r) => r.attached), false);
    expect(children.sublist(42, 60).every((RenderBox r) => r.attached), true);
  });

  test('RenderSliverPadding calculates correct geometry', () {
    // Viewport is 800x600, each item is 100px high with 50px before and after = 200px

    final List<RenderSliverToBoxAdapter> adapters = <RenderSliverToBoxAdapter>[];
    final List<RenderSliverPadding> paddings = new List<RenderSliverPadding>.generate(30, (int index) {
      RenderSliverToBoxAdapter adapter;
      final RenderSliverPadding padding = new RenderSliverPadding(
        padding: const EdgeInsets.symmetric(vertical: 50.0),
        child: adapter = new RenderSliverToBoxAdapter(
          child: new RenderSizedBox(const Size(400.0, 100.0)),
        ),
      );
      adapters.add(adapter);
      return padding;
    });


    final RenderViewport root = new RenderViewport(
      axisDirection: AxisDirection.down,
      crossAxisDirection: AxisDirection.right,
      offset: new ViewportOffset.zero(),
      cacheExtent: 250.0,
      children: paddings,
    );
    layout(root);

    RenderSliverPadding firstVisiblePadding = paddings[0];
    expectSliverConstraints(
      sliver: firstVisiblePadding,
      cacheOrigin: 0.0,
      remainingPaintExtent: 600.0,
      remainingCacheExtent: 600.0 + 250.0,
      scrollOffset: 0.0,
    );
    expectSliverGeometry(
      sliver: firstVisiblePadding,
      paintExtent: 200.0,
      cacheExtent: 200.0,
      visible: true,
    );
    RenderSliverToBoxAdapter firstVisiblePadded = adapters[0];
    expectSliverConstraints(
      sliver: firstVisiblePadded,
      cacheOrigin: 0.0,
      remainingPaintExtent: 550.0,
      remainingCacheExtent: 600.0 + 250.0 - 50.0,
      scrollOffset: 0.0,
    );
    expectSliverGeometry(
      sliver: firstVisiblePadded,
      paintExtent: 100.0,
      cacheExtent: 100.0,
      visible: true,
    );

    RenderSliverPadding lastVisiblePadding = paddings[2];
    expectSliverConstraints(
      sliver: lastVisiblePadding,
      cacheOrigin: 0.0,
      remainingPaintExtent: 200.0,
      remainingCacheExtent: 200.0 + 250.0,
      scrollOffset: 0.0,
    );
    expectSliverGeometry(
      sliver: lastVisiblePadding,
      paintExtent: 200.0,
      cacheExtent: 200.0,
      visible: true,
    );
    RenderSliverToBoxAdapter lastVisiblePadded = adapters[2];
    expectSliverConstraints(
      sliver: lastVisiblePadded,
      cacheOrigin: 0.0,
      remainingPaintExtent: 150.0,
      remainingCacheExtent: 200.0 + 250.0 - 50.0,
      scrollOffset: 0.0,
    );
    expectSliverGeometry(
      sliver: lastVisiblePadded,
      paintExtent: 100.0,
      cacheExtent: 100.0,
      visible: true,
    );

    final RenderSliverPadding firstCachePadding = paddings[3];
    expectSliverConstraints(
      sliver: firstCachePadding,
      cacheOrigin: 0.0,
      remainingPaintExtent: 0.0,
      remainingCacheExtent: 250.0,
      scrollOffset: 0.0,
    );
    expectSliverGeometry(
      sliver: firstCachePadding,
      paintExtent: 0.0,
      cacheExtent: 200.0,
      visible: false,
    );
    final RenderSliverToBoxAdapter firstCachePadded = adapters[3];
    expectSliverConstraints(
      sliver: firstCachePadded,
      cacheOrigin: 0.0,
      remainingPaintExtent: 0.0,
      remainingCacheExtent: 250.0 - 50.0,
      scrollOffset: 0.0,
    );
    expectSliverGeometry(
      sliver: firstCachePadded,
      paintExtent: 0.0,
      cacheExtent: 100.0,
      visible: false,
    );

    final RenderSliverPadding lastCachePadding = paddings[4];
    expectSliverConstraints(
      sliver: lastCachePadding,
      cacheOrigin: 0.0,
      remainingPaintExtent: 0.0,
      remainingCacheExtent: 50.0,
      scrollOffset: 0.0,
    );
    expectSliverGeometry(
      sliver: lastCachePadding,
      paintExtent: 0.0,
      cacheExtent: 50.0,
      visible: false,
    );
    final RenderSliverToBoxAdapter lastCachePadded = adapters[4];
    expectSliverConstraints(
      sliver: lastCachePadded,
      cacheOrigin: 0.0,
      remainingPaintExtent: 0.0,
      remainingCacheExtent: 0.0,
      scrollOffset: 0.0,
    );
    expectSliverGeometry(
      sliver: lastCachePadded,
      paintExtent: 0.0,
      cacheExtent: 0.0,
      visible: false,
    );

    // scroll first padding off screen
    root.offset = new ViewportOffset.fixed(50.0);
    pumpFrame();

    firstVisiblePadding = paddings[0];
    expectSliverConstraints(
      sliver: firstVisiblePadding,
      cacheOrigin: -50.0,
      remainingPaintExtent: 600.0,
      remainingCacheExtent: 50.0 + 600.0 + 250.0,
      scrollOffset: 50.0,
    );
    expectSliverGeometry(
      sliver: firstVisiblePadding,
      paintExtent: 150.0,
      cacheExtent: 200.0,
      visible: true,
    );
    firstVisiblePadded = adapters[0];
    expectSliverConstraints(
      sliver: firstVisiblePadded,
      cacheOrigin: 0.0,
      remainingPaintExtent: 600.0,
      remainingCacheExtent: 600.0 + 250.0,
      scrollOffset: 0.0,
    );
    expectSliverGeometry(
      sliver: firstVisiblePadded,
      paintExtent: 100.0,
      cacheExtent: 100.0,
      visible: true,
    );

    // scroll to the end
    root.offset = new ViewportOffset.fixed(5400.0);
    pumpFrame();


    final RenderSliverPadding firstPadding = paddings[0];
    expectSliverConstraints(
      sliver: firstPadding,
      cacheOrigin: -250.0,
      remainingPaintExtent: 600.0,
      remainingCacheExtent: 250.0 + 600.0 + 250.0,
      scrollOffset: 5400.0,
    );
    expectSliverGeometry(
      sliver: firstPadding,
      paintExtent: 0.0,
      cacheExtent: 0.0,
      visible: false,
    );
    final RenderSliverToBoxAdapter firstPadded = adapters[0];
    expectSliverConstraints(
      sliver: firstPadded,
      cacheOrigin: -200.0,
      remainingPaintExtent: 600.0,
      remainingCacheExtent: 250.0 + 600.0 + 250.0,
      scrollOffset: 5350.0,
    );
    expectSliverGeometry(
      sliver: firstPadded,
      paintExtent: 0.0,
      cacheExtent: 0.0,
      visible: false,
    );

    final RenderSliverPadding firstPreCachePadding = paddings[25];
    expectSliverConstraints(
      sliver: firstPreCachePadding,
      cacheOrigin: -250.0,
      remainingPaintExtent: 600.0,
      remainingCacheExtent: 250.0 + 600.0 + 250.0,
      scrollOffset: 400.0,
    );
    expectSliverGeometry(
      sliver: firstPreCachePadding,
      paintExtent: 0.0,
      cacheExtent: 50.0,
      visible: false,
    );
    final RenderSliverToBoxAdapter firstPreCachePadded = adapters[25];
    expectSliverConstraints(
      sliver: firstPreCachePadded,
      cacheOrigin: -200.0,
      remainingPaintExtent: 600.0,
      remainingCacheExtent: 250.0 + 600.0 + 250.0,
      scrollOffset: 350.0,
    );
    expectSliverGeometry(
      sliver: firstPreCachePadded,
      paintExtent: 0.0,
      cacheExtent: 0.0,
      visible: false,
    );

    final RenderSliverPadding lastPreCachePadding = paddings[26];
    expectSliverConstraints(
      sliver: lastPreCachePadding,
      cacheOrigin: -200.0,
      remainingPaintExtent: 600.0,
      remainingCacheExtent: 200.0 + 600.0 + 250.0,
      scrollOffset: 200.0,
    );
    expectSliverGeometry(
      sliver: lastPreCachePadding,
      paintExtent: 0.0,
      cacheExtent: 200.0,
      visible: false,
    );
    final RenderSliverToBoxAdapter lastPreCachePadded = adapters[26];
    expectSliverConstraints(
      sliver: lastPreCachePadded,
      cacheOrigin: -150.0,
      remainingPaintExtent: 600.0,
      remainingCacheExtent: 150.0 + 600.0 + 250.0,
      scrollOffset: 150.0,
    );
    expectSliverGeometry(
      sliver: lastPreCachePadded,
      paintExtent: 0.0,
      cacheExtent: 100.0,
      visible: false,
    );

    lastVisiblePadding = paddings[29];
    expectSliverConstraints(
      sliver: lastVisiblePadding,
      cacheOrigin: 0.0,
      remainingPaintExtent: 200.0,
      remainingCacheExtent: 200.0 + 250.0,
      scrollOffset: 0.0,
    );
    expectSliverGeometry(
      sliver: lastVisiblePadding,
      paintExtent: 200.0,
      cacheExtent: 200.0,
      visible: true,
    );
    lastVisiblePadded = adapters[29];
    expectSliverConstraints(
      sliver: lastVisiblePadded,
      cacheOrigin: 0.0,
      remainingPaintExtent: 150.0,
      remainingCacheExtent: 150.0 + 250.0,
      scrollOffset: 0.0,
    );
    expectSliverGeometry(
      sliver: lastVisiblePadded,
      paintExtent: 100.0,
      cacheExtent: 100.0,
      visible: true,
    );
  });
}

void expectSliverConstraints({RenderSliver sliver, double cacheOrigin, double remainingPaintExtent, double remainingCacheExtent, double scrollOffset}) {
  expect(sliver.constraints.cacheOrigin, cacheOrigin, reason: 'cacheOrigin');
  expect(sliver.constraints.remainingPaintExtent, remainingPaintExtent, reason: 'remainingPaintExtent');
  expect(sliver.constraints.remainingCacheExtent, remainingCacheExtent, reason: 'remainingCacheExtent');
  expect(sliver.constraints.scrollOffset, scrollOffset, reason: 'scrollOffset');
}

void expectSliverGeometry({RenderSliver sliver, double paintExtent, double cacheExtent, bool visible}) {
  expect(sliver.geometry.paintExtent, paintExtent, reason: 'paintExtent');
  expect(sliver.geometry.cacheExtent, cacheExtent, reason: 'cacheExtent');
  expect(sliver.geometry.visible, visible, reason: 'visible');
}

class TestRenderSliverBoxChildManager extends RenderSliverBoxChildManager {
  TestRenderSliverBoxChildManager({
    this.children,
  });

  RenderSliverMultiBoxAdaptor _renderObject;
  List<RenderBox> children;

  RenderSliverList createRenderSliverList() {
    assert(_renderObject == null);
    _renderObject = new RenderSliverList(childManager: this);
    return _renderObject;
  }

  RenderSliverFixedExtentList createRenderSliverFixedExtentList() {
    assert(_renderObject == null);
    _renderObject = new RenderSliverFixedExtentList(
      childManager: this,
      itemExtent: 100.0,
    );
    return _renderObject;
  }

  RenderSliverGrid createRenderSliverGrid() {
    assert(_renderObject == null);
    _renderObject = new RenderSliverGrid(
      childManager: this,
      gridDelegate: const SliverGridDelegateWithFixedCrossAxisCount(
        crossAxisCount: 2,
        childAspectRatio: 4.0,
      ),
    );
    return _renderObject;
  }

  int _currentlyUpdatingChildIndex;

  @override
  void createChild(int index, { @required RenderBox after }) {
    if (index < 0 || index >= children.length)
      return null;
    try {
      _currentlyUpdatingChildIndex = index;
      _renderObject.insert(children[index], after: after);
    } finally {
      _currentlyUpdatingChildIndex = null;
    }
  }

  @override
  void removeChild(RenderBox child) {
    _renderObject.remove(child);
  }

  @override
  double estimateMaxScrollOffset(SliverConstraints constraints, {
    int firstIndex,
    int lastIndex,
    double leadingScrollOffset,
    double trailingScrollOffset,
  }) {
    assert(lastIndex >= firstIndex);
    return children.length * (trailingScrollOffset - leadingScrollOffset) / (lastIndex - firstIndex + 1);
  }

  @override
  int get childCount => children.length;

  @override
  void didAdoptChild(RenderBox child) {
    assert(_currentlyUpdatingChildIndex != null);
    final SliverMultiBoxAdaptorParentData childParentData = child.parentData;
    childParentData.index = _currentlyUpdatingChildIndex;
  }

  @override
  void setDidUnderflow(bool value) { }
}