In Industry 4.0 large-scale discrete event systems (DES) are becoming increasingly dependent on internet of things (IoT) based real-time distributed supervisory control systems. In order to meet the IoT growing demand, new technologies and skills are being developed which require an automated systematic testing to achieve success in adoption. Testing such systems requires an integration of computation, communication and control in the test architecture. This may pose number of issues that may not be suitably addressed by traditional centralized test architectures. In this paper, a distributed test framework for testing distributed real-time systems is presented, where online monitors (executable code as annotations) are integrated to systems to record relevant events. The proposed test architecture is more scalable than centralized architectures in the sense of timing constraints and geographical distribution. By assuming the existence of a coverage correct centralized remote tester, we give a partitioning algorithm of it to produce distributed local testers which enables to meet more flexible performance constraints while preserving the remote tester's functionality. The proposed approach not only preserves the correctness of the centralized tester but also allows to meet stronger timing constraints for solving test controllability and observability issues. The effectiveness of the proposed architecture is demonstrated by an illustrative example.