Oh, yes. The constructors!
I missed that. Thank you.

Could you add a small tests for this too? Have a look at AddToList.php, AddToList.config.php, AddToList.output.php and add something similar (but simpler) to that. I can help out if you need me to.

Well thank you for the ConfigBuilder 😁

Could I just replace

$config->messenger([
    'routing' => [
        'Foo\\Message' => [
            'senders' => ['workqueue'],
        ],
        'Foo\\DoubleMessage' => [
            'senders' => ['sync', 'workqueue'],
        ],
    ]
]);

?

Sure, but dont replace anything. Just add a third message.

$config->messenger([
    'routing' => [
        'Foo\\MyArrayMessage' => [
            'senders' => ['workqueue'],
        ],
    ]
]);
 $config->messenger() 
     ->routing('Foo\\Message')->senders(['workqueue']); 
 $config->messenger() 
     ->routing('Foo\\DoubleMessage')->senders(['sync', 'workqueue']); 

Done 👌

Travis failure seems unrelated.

Thanks for fixing this bug Mathieu.