sliver_persistent_header_test.dart

import 'package:flutter/material.dart';
import 'package:flutter_test/flutter_test.dart';

void main() {
  testWidgets('SliverPersistentHeader - floating+pinned - inner scroll should not be overlapped by header', (WidgetTester tester) async {
    final GlobalKey _headerKey = new GlobalKey();
    final GlobalKey _subHeaderKey = new GlobalKey();
    final HeaderDelegate _headerDelegate = new HeaderDelegate();
    await tester.pumpWidget(
      new NestedScrollView(
          headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
            return [
              new SliverPersistentHeader(
                key: _headerKey,
                delegate: _headerDelegate,
                pinned: true,
                floating: true,
              )
            ];
          },
          body: new Stack(children: <Widget>[
            new ListView.builder(
              itemBuilder: (BuildContext context, int index) {
                return new Container(
                  color: Colors.red,
                  child: new Text("aaa${index}"),
                );
              },
              itemCount: 100,
            ),
            new Container(
              key: _subHeaderKey,
              color: Colors.black26,
              child: const Text('hhh'),
            )
          ])),
    );

    // Verify position first, offset should be same as maxExtent from persistent header
    expect(tester.getTopLeft(find.text('hhh')), new Offset(0.0, _headerDelegate.maxExtent));

    // Start scrolling
    final Offset point = tester.getCenter(find.text('aaa3'));
    // Creating gesture
    final TestGesture gesture = await tester.startGesture(point);
    await tester.pump(const Duration(milliseconds: 5000));

    // Scroll on 100 px down
    await gesture.moveBy(const Offset(0.0, -100.0));
    await tester.pump(const Duration(milliseconds: 10));

    // Offset should be as minExtent from persistent header
    expect(tester.getTopLeft(find.text('hhh')), new Offset(0.0, _headerDelegate.minExtent));

    // Scroll 100 px down more
    await gesture.moveBy(const Offset(0.0, 100.0));
    await tester.pump(const Duration(milliseconds: 10));

    // Offset should kepp staying same as minExtent from persistent header
    expect(tester.getTopLeft(find.text('hhh')), new Offset(0.0, _headerDelegate.minExtent));
  });
}

class HeaderDelegate extends SliverPersistentHeaderDelegate {
  @override
  double get maxExtent => 200.0;

  @override
  double get minExtent => 100.0;

  @override
  Widget build(
      BuildContext context, double shrinkOffset, bool overlapsContent) {
    return new Container(
      height: maxExtent,
      color: Colors.black26,
    );
  }

  @override
  bool shouldRebuild(HeaderDelegate oldDelegate) => false;
}