In larger integrated systems, the overall system is comprised of subsystems or large components. Each of these subsystems was tested during Component Integration Testing to confirm it performs properly when taken on its own. Systems Integration testing confirms that the subsystem or components interact as designed and as required once integrated together. For example, a Systems Integration test of a material handling system’s emergency stop system would confirm that each subsystem stops and that each component subsystem turns on its e-stop indicators.

Since the goal of Systems Integration Testing is to confirm the interactions between subsystems, most tests confirm the interfaces between the subsystems and complex responses to stimuli. In many cases, testing requires stimulating the inputs to one subsystem and observing the outputs of another. Modeling the system simplifies identifying these interactions.

For Model Driven Systems Engineering projects, the activity diagrams developed during Design Synthesis allocate functional (actions) to the subsystems (swim lanes). Following the paths through the activity diagrams identify the functionality of the necessary test scenarios. Note that each path can be represented as a sequence diagram. The control flows and object flows that cross the swim lane boundaries represent the interfaces between the subsystems.