Re-executing the old test cases across multiple releases or built to make sure that changes or bug fixes has not affected the existing functionalities is known as regression testing.

5 Strategies should be remember while doing regression:

1. Regression testing should be done whenever changes are made in a code or a defect is fixed, it should be perform regularly to replicate defects.
2. Defects must be reported accurately as new code sometimes creates old defects again.
3. If automation can be possible for testing on regression suite,its great to do.
4. Always perform non-functional testings: usability, portability, and performance testing.
5. Always Test data should be changed. Dont run the same test data in the exact same order every time.