Flutter integration test - Check icon type has changed when pressing list row

I'm trying out flutter and I've basically followed along with the getting started Codelabs

• https://flutter.dev/docs/get-started/codelab
• https://codelabs.developers.google.com/codelabs/first-flutter-app-pt2/#0

But I'm attempting to add some integration tests to it. Basically what I want is to check if the icon is Icons.favourite when the list row is pressed. All other examples I've come across see only checks for text on a screen. Heres the test file:

import 'package:flutter_driver/flutter_driver.dart';
import 'package:test/test.dart';

void main() {
  group('My App', () {
    final firstListItem = find.byValueKey('list_title_0');

    FlutterDriver driver;

    setUpAll(() async {
      driver = await FlutterDriver.connect();
    });

    tearDownAll(() async {
      if (driver != null) {
        driver.close();
      }
    });

    test('name is favourited', () async {
      await driver.tap(firstListItem);

      final SerializableFinder firstFavourite = find.byValueKey('favourite_0_saved');

      await driver.waitFor(firstFavourite);

      // not sure what to expect for here..
    });
  });
}

Below is the code for the app. It's Basically the codelabs code. The only change I've made is the addition of key to Icon so I can use it for the finder during testing.

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

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Startup Name Generator',
      home: RandomWords(),
    );
  }
}

class RandomWords extends StatefulWidget {
  @override
  RandomWordsState createState() => RandomWordsState();
}

class RandomWordsState extends State<RandomWords> {
  final _suggestions = <WordPair>[];
  final Set<WordPair> _saved = Set<WordPair>();
  final _biggerFont = const TextStyle(fontSize: 18.0);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Startup Name Generator'),
        actions: <Widget>[
          IconButton(icon: Icon(Icons.list), onPressed: _pushSaved),
        ],
      ),
      body: _buildSuggestions(),
    );
  }

  void _pushSaved() {
    Navigator.of(context).push(
      MaterialPageRoute<void>(builder: 
        (BuildContext context) {
          final Iterable<ListTile> tiles = _saved.map((WordPair pair) {
            return ListTile(
              title: Text(
                pair.asPascalCase,
                style: _biggerFont,
              ),
            );
          });
          final List<Widget> divided = ListTile.divideTiles(
            context: context,
            tiles: tiles
          ).toList();

          return Scaffold(
            appBar: AppBar(
              title: Text('Saved Suggestions'),
            ),
            body: ListView(children: divided),
          );
        }
      )
    );
  }

  Widget _buildSuggestions() {
    return ListView.builder(
      padding: const EdgeInsets.all(16.0),
      itemBuilder: (context, i) {
        if (i.isOdd) return Divider();

        final index = i ~/ 2;
        if (index >= _suggestions.length) {
          _suggestions.addAll(generateWordPairs().take(10));
        }
        return _buildRow(_suggestions[index], i);
      },
    );
  }

  Widget _buildRow(WordPair pair, int i) {
    final bool alreadySaved = _saved.contains(pair);

    return ListTile(
      title: Text(
        pair.asPascalCase,
        style: _biggerFont,
      ),
      key: Key('list_title_$i'),
      trailing: Icon(
        alreadySaved ? Icons.favorite : Icons.favorite_border,
        color: alreadySaved ? Colors.red : null,
        key: alreadySaved ? Key('favourite_${i}_saved') : Key('favourite_${i}_unsaved'),
      ),
      onTap: () {
        setState(() {
          if (alreadySaved) {
            _saved.remove(pair);
          } else {
            _saved.add(pair);
          }
        });
      },
    );
  }
}