System testing is probably the most important phase of complete testing cycle. This phase is started after the completion of other phases like Unit, Component and Integration testing. During the System Testing phase, non functional testing also comes in to picture and performance, load, stress, scalability all these types of testing are performed in this phase.

By Definition, System Testing is conducted on the complete integrated system and on a replicated production environment. System Testing also evaluates that system compliance with specific functional and non functional requirements both.