The increasing complexity of software in production systems leads to a growing relevance of testing. This trend will continue due to the flexibilization, and IT networking of production systems. This paper proposes a discussion about the requirements of future production systems which will be reconfigurable, decentralized controlled and will consist of autonomous components. From these predicted requirements, new challenges for functional testing are derived. To elucidate these challenges, three use cases illustrate when testing measures will be necessary within the operation phase of production systems.