Widget layout

main.dart

import 'package:flutter_web/material.dart';
import 'package:flutter_web_test/flutter_web_test.dart';
import 'package:flutter_web_ui/ui.dart' as ui;

// MyWidget displays a silver, horizontal box
// StatelessWidget indicates the UI is built from fixed data
class MyWidget extends StatelessWidget {
  @override
// BuildContext enables parent-child relationships between widgets
  Widget build(BuildContext context) {   
// Row is a parent widget to the BlueBox widget  
    return Row(      
      children: [
// BlueBox is a child widget to the Row widget
        BlueBox(),
      ],
    );
  }
}

// BlueBox displays a blue square
class BlueBox extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
// Container enables customizable widgets 
    return Container(
      width: 50,
      height: 50,
      decoration: BoxDecoration(
        color: Colors.blue,
        border: Border.all(),
      ),
    );
  }
}

test.dart

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Directionality(
      textDirection: TextDirection.ltr,
      child: Container(
        color: Color(0xffeeeeee),
        child: Center(
          child: Container(
            child: MyWidget(),
            color: Color(0xffcccccc),
          ),
        ),
      ),
    );
  }
}

Future<void> main() async {
  await ui.webOnlyInitializePlatform();
  
  runApp(MyApp());

  final controller = LiveWidgetController(WidgetsBinding.instance);

  final rows = controller.widgetList(find.byType(Row));

  if (rows.length == 0) {
    _result(false, ['Couldn\'t find a Row!']);
    return;
  }

  if (rows.length > 1) {
    _result(false, ['Found ${rows.length} Rows, rather than just one.']);
    return;
  }

  final row = rows.first as Row;

  if (row.children.length != 1 || row.children.any((w) => w is! BlueBox)) {
    _result(false, ['The Row should have one child, a BlueBox widget.']);
    return;
  }

  _result(true, ['A Row with one BlueBox widget.']);
}