System integration testing (SIT) involves the overall testing of a complete system of many subsystem components or elements. 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." Following integration, system test is a process of "verifying that the system meets its requirements, and validating that the system performs in accordance with the customer or user expectations."
