Automated driving functions and intelligent assistance systems have become an integral part of our everyday lives. In the future, traffic will be even more characterised by them. But how can we trust automated vehicles? The answer from the DLR Institute of Transportation Systems is clear: the testing of automated driving functions must also continue to develop so that it can guarantee safety. Simulation is becoming increasingly important for this, but testing in real traffic is also essential in order to validate the results of the simulation. To this end, the institute has built up an extensive landscape of large-scale research facilities (Test Bed Lower Saxony) and is developing solutions for testing future automated road users in numerous projects.