Developing and testing software and configuration variants for Industrial Internet of Things (IIoT) applications & systems is a challenge. The systems can be physically large, and often contain 1000s of nodes, which is tough to manage in a physical lab. Testing software that will run across these nodes requires the ability to automate, inspect and control tests, but automating tests across hordes of physical machines is not easy. These challenges can be overcome by using virtual platforms and simulations of wireless networks and the environment. This converts the difficult hardware into software simulations that can be created, configured, and controlled with ease. In this session, we cover the techniques for IoT system simulation and testing that we have developed and discovered over the past year, and how to build scalable testing systems.