What kind of testing would provide evidence for the successful completion of a project phase?

System testing is designed to validate the entire system's behavior against specified requirements. It is a comprehensive form of testing that evaluates the end-to-end specifications of an application after all components have been integrated. This type of testing ensures that the system meets the stated requirements and performs as expected when it is subjected to realistic usage scenarios.

Completing system testing provides significant evidence that a project phase has been successfully completed, as it confirms that the application operates as a whole and delivers the desired functionality. Since it looks at the system in its entirety, it offers insights into overall behavior, performance, security, and usability.

Unit testing focuses on individual components or modules, and while it verifies the correctness of specific pieces of code, it does not provide insight into how these components function together. Integration testing assesses interactions between components but does not cover the full system behavior or overall requirements. Regression testing, on the other hand, checks for defects in existing functionalities after changes have been made, but it does not necessarily signify the completion of a project phase. Thus, system testing is the most suitable approach for demonstrating that the project phase is complete.