Explanation
According to the Project Management Professional (PMP) Reference Materials, a stakeholder register is a tool that the project manager should have used to prevent this situation. A stakeholder register is a document that identifies and analyzes the project stakeholders, their roles, interests, expectations, influence, and communication needs. A stakeholder register helps the project manager to plan and manage stakeholder engagement, and ensure that the project meets the stakeholder requirements and expectations. A stakeholder register also helps the project manager to identify and address any potential conflicts, risks, or issues that may arise from the stakeholder involvement. By using a stakeholder register, the project manager could have avoided the situation where a key stakeholder did not receive the functionality test status reports, and noticed that an important functionality for their area was not tested. The project manager could have ensured that the stakeholder was properly informed and involved in the testing process, and that their feedback and approval were obtained before moving to the next phase of the project. References: Project Management Professional (PMP) Exam Content Outline, A Guide to the Project Management Body of Knowledge (PMBOK Guide) - Seventh Edition, Stakeholder Register.