Question:

What if you do container->get() some services in tests.

Answer:

The proper solution would be to create a public alias for the service you want to test in the test environment only:

# app/config/config_test.yml
services:
    test_alias.AppBundle\Service\MyService:
        alias: 'AppBundle\Service\MyService'
        public: true # require on SF4, where everything is private by default

Then, you would actually fetch test_alias.AppBundle\Service\MyService out of the container in your unit test. It's a nice idea too: you only need to expose your service as public in the test environment.