Modify axis size

main.dart

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

class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Row(
      mainAxisSize: MainAxisSize.max,
      children: [
        BlueBox(),
        BlueBox(),
        BlueBox(),
      ],
    );
  }
}

class BlueBox extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    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 {
  final completer = Completer<void>();
  
  runApp(MyApp());

  WidgetsFlutterBinding.ensureInitialized()
      .addPostFrameCallback((timestamp) async {
    completer.complete();
  });
  
  await completer.future;

  final controller = LiveWidgetController(WidgetsBinding.instance);

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

  if (rows.length == 0) {
    _result(false, ['Couldn\'t find 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.mainAxisSize != MainAxisSize.min) {
    _result(false, ['Row lays out the BlueBox widgets with extra space. Change MainAxisSize.max to MainAxisSize.min']);
    return;
  }
  
  if (row.children.length != 3 || row.children.any((w) => w is! BlueBox)) {
    _result(false, ['There should only be three children, all BlueBox widgets.']);
    return;
  }

  _result(true, ['Row lays out the BlueBox widgets without extra space, and the BlueBox widgets are positioned at the middle of Row\'s main axis.']);
}