System testing is the process of verification of the modular systems for the functionality they are programmed for. A system consists of a set of units thoroughly unit tested and seamlessly integrated with reusable components and libraries to possess the business requirements for that system. The following diagram shows the integration of elementary components (units) that make a system that should be tested with the request content as input and executing it to get the desired system output:

The preceding diagram represents a system components as a series of units integrated with multiple operations to be performed in them. A system receives the request content that needs to be processed by each unit that the request content is sent for; failure at any unit should stop the processing of that message and give a corresponding failure message. Once all the units and operations process the message, it can be given as the output from that system.

With system testing, the system is tested for a set of valid and invalid request content and the behavior is recorded. Based on the failure scenarios and criticality of those defects, the development team needs to fix them based on priority and handover the corrected system for another round of testing.