System testing tests an integrated system to verify/validate that it meets its requirements.
System testing is testing conducted on a complete, integrated system to evaluate the system's compliance with its specified requirements. System testing falls within the scope of black box testing, and as such, should require no knowledge of the inner design of the code or logic.
As a rule, system testing takes, as its input, all of the "integrated" software components that have successfully passed integration testing and also the software system itself integrated with any applicable hardware system(s). The purpose of integration testing is to detect any inconsistencies between the software units that are integrated together (called assemblages) or between any of the assemblages and the hardware. System testing is a more limiting type of testing; it seeks to detect defects both within the "inter-assemblages" and also within the system as a whole.
Testing the Whole System:
System testing is actually done to the entire system against the Functional Requirement Specification(s) (FRS) and/or the System Requirement Specification (SRS). Moreover, the System testing is an investigatory testing phase, where the focus is to have almost a destructive attitude and test not only the design, but also the behaviour and even the believed expectations of the customer. It is also intended to test up to and beyond the bounds defined in the software/hardware requirements specification(s).
