  Internet of Things (IoT) applications promise to make many aspects of our
lives more efficient and adaptive through the use of distributed sensing and
computing nodes. A central aspect of such applications is their complex
communication behavior that is heavily influenced by the physical environment
of the system. To continuously improve IoT applications, a staging environment
is needed that can provide operating conditions representative of deployments
in the actual production environments -- similar to what is common practice in
cloud application development today. Towards such a staging environment, we
present Marvis, a framework that orchestrates hybrid testbeds, co-simulated
domain environments, and a central network simulation for testing distributed
IoT applications. Our preliminary results include an open source prototype and
a demonstration of a Vehicle-to-everything (V2X) communication scenario.
