Wireless communication technologies between cars and infrastructure (Car2X communication) will play a major role for future driver assistance. Many new applications and services in the fields of vehicle safety, comfort and infotainment will be possible. New test and evaluation procedures are required to cover future cooperative traffic scenarios with many cars and infrastructure equipment involved. An enrichment of real test situations with simulated environment scenarios (“Extended Reality”) is proposed as an approach to develop and test such systems. An integrated development and test environment provides a flexible and configurable combination of both, real and simulated units including OnBoardUnits, RoadSideUnits, MonitoringDevices and on-board displays with modules e. g. for wireless communication (WAVE, DSRC, WLAN, UMTS), positioning (GPS), vehicle and infrastructure interfaces (CAN-Bus), which can be combined in any manner. Based on the integrated architecture a real Car2X testing scenario consisting of a car communicating with RoadSideUnit(s) providing traffic sign and traffic light information was first developed and tested in full simulation mode in the lab. Then the same scenario was validated in a real test car on the real test track of the Connected Vehicle Proving Center in USA still with a simulated infrastructure environment. Based on that received information warning messages appeared on the on-board display. Active driver assistance functions can be triggered as well. The novel approach allows evaluation of the technology benefits and effectiveness with significantly reduced efforts as compared to traditional operational testing methods. This paper will cover the technology employed; the assistance and safety scenarios evaluated and give an outlook on the future use of the technology in combination with field operational tests.