FILE: lib/todo.dart
class Todo {
  Todo(this.title, {this.done = false});

  final String title;
  final bool done;

  Todo toggled() => Todo(title, done: !done);
}
END_FILE
FILE: test/todo_test.dart
import 'package:flutter_test/flutter_test.dart';
import 'package:todo_app/todo.dart';

void main() {
  test('toggled flips done', () {
    expect(Todo('a').toggled().done, isTrue);
  });
}
END_FILE
