Once a bug is fixed, it should be retested.

Confirmation testing, also known as re-testing, is the process of testing a defect that has been fixed to verify that it has been resolved and does not affect other parts of the system. Confirmation testing is usually done by the same tester who reported the defect and using the same test case that revealed the defect. You can find more information about confirmation testing in A Study Guide to the ISTQB® Foundation Level 2018 Syllabus, Chapter 3, Section 3.21.