The development of Advanced Driver Assistance Systems (ADAS) requires a controlled testing environment for evaluating perception, decision-making, and control algorithms. This paper presents a connected infrastructure for ADAS testing, integrating roadside LiDAR and stereo cameras, a 5G-based communication network, and an instrumented prototype vehicle. The development included both a digital twin for virtual testing and a physically instrumented real-world area. The system supports key scenarios, including automated parking, safety-focused ADAS for Vulnerable Road Users (VRUs), and collaborative localization. A case study on LiDAR-based cooperative localization demonstrates improved positioning accuracy, highlighting the benefits of the connected infrastructure for autonomous driving and the potential of a custom-designed test area for this type of applications.