sliver_stack_issue_repo_test.dart

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

void main() {
  testWidgets('This succeeds', (tester) async {
    var result = 0;

    final sut = MaterialApp(
      home: Scaffold(
        body: Center(
          child: CustomScrollView(
            slivers: [
              SliverStack(
                children: [
                  SliverToBoxAdapter(
                    child: SizedBox(
                      height: 400,
                      width: 400,
                    ),
                  ),
                  SliverToBoxAdapter(
                    child: TextButton(
                      child: Text('test'),
                      onPressed: () {
                        result++;
                      },
                    ),
                  )
                ],
              )
            ],
          ),
        ),
      ),
    );

    await tester.pumpWidget(sut);
    await tester.pumpAndSettle();

    await tester.tap(find.text('test'));
    await tester.pumpAndSettle();

    expect(result, 1);
  });

  testWidgets('this fail', (tester) async {
    var result = 0;

    final sut = MaterialApp(
      home: Scaffold(
        body: Center(
          child: CustomScrollView(
            slivers: [
              SliverStack(
                children: [
                  SliverToBoxAdapter(
                    child: SizedBox(
                      height: 100,
                      width: 400,
                    ),
                  ),
                  SliverPositioned(
                    left: 40,
                    right: 40,
                    top: 225,
                    child: TextButton(
                      child: Text('test'),
                      onPressed: () {
                        result++;
                      },
                    ),
                  ),
                ],
              )
            ],
          ),
        ),
      ),
    );

    await tester.pumpWidget(sut);
    await tester.pumpAndSettle();

    await tester.tap(find.text('test'));
    await tester.pumpAndSettle();

    expect(result, 1);
  });
}