In Symfony 4.1 appeared nice feature: https://symfony.com/blog/new-in-symfony-4-1-simpler-service-testing
As mentioned symfony/symfony#26499 (comment) removing unused private services from test.service_container is intended behaviour.

In my bundle (call it bundle A) I've private service which will be type-hinted in other bundles, but not in bundle A.
Is there optimal way to write tests for this service in bundle A?