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

The correct choice of system testing is appropriate because it encompasses the evaluation of the entire system's behavior against the specified requirements. System testing is performed after integration testing and is intended to validate that the integrated system meets the intended use and functionality within a complete environment. This level of testing simulates real-world usage and ensures that all components work together as expected, thereby providing tangible evidence that the project phase has been completed successfully.

In the context of project management and software development, system testing serves as the final check before the software goes live or is handed off to stakeholders. It verifies that the system functions as intended in terms of performance, usability, and reliability, which collectively provides assurance that the project is ready to advance to the next phase or to be delivered.

Unit testing focuses on individual components in isolation and may not reflect overall project completion since it's just one aspect of the development process. Integration testing checks the interactions between components, but it does not address the system as a whole. Regression testing, while important for ensuring previously functioning features continue to work, is more about confirming existing functionality rather than demonstrating the successful completion of a project phase. Thus, system testing is the most suitable choice for providing evidence of project phase completion.