The system under test may be composed of electromechanical or computer hardware, or software, or hardware with embedded software, or hardware/software with human-in-the-loop testing.
SIT is typically performed on a larger integrated system of components and subassemblies that have previously undergone subsystem testing.
SIT consists, initially, of the "process of assembling the constituent parts of a system in a logical, cost-effective way, comprehensively checking system execution (all nominal and exceptional paths), and including a full functional check-out.
"[1] In technology product development, the beginning of system integration testing is often the first time that an entire system has been assembled such that it can be tested as a whole.
With multiple integrated systems, assuming that each have already passed system testing,[2] SIT proceeds to test their required interactions.