The fundamental test process activity where the sufficiency of testing and resulting information are assessed is Evaluating exit criteria and reporting. This activity involves checking whether the test objectives have been met and whether there are any unresolved issues or risks that could affect the release or deployment decision.
This activity also involves preparing and communicating a test summary report that summarizes the test activities and results and provides recommendations and feedback for improvement. You can find more information about Evaluating exit criteria and reporting in [A Study Guide to the ISTQB Foundation Level
2018 Syllabus], Chapter 3, Section 3.5.