Data Distribution Service (DDS) is a communication middleware standard based on a publish-subscribe model for composable, scalable, real-time, dependent applications. As a result, it is very useful in industrial IoT (IIoT) applications that demand high communication quality. The major challenge in DDS application development is that DDS programming is quite different from traditional socket programming and RPC programming. In addition, DDS programming involves complex QoS settings, which may affect application behavior in many aspects, such as reliability and scalability. Therefore, it is hard to know how a DDS-based application will perform in the design phase. To this end, we present a DDS-based emulator, namely the IIoT Testbed. The application developers can use the VI of the IIoT Testbed to create a DDS application prototype with QoS settings in a short time, and then obtain performance results by emulations. With the help of the emulator, the developers can easily understand several non-functional properties of their design and adjust the design accordingly.