Overview
Regression testing is essential whenever code is modified, whether for a new feature, a bug fix, or refactoring. It ensures that the changes haven't introduced new bugs in existing functionality.
Automation
Because regression testing involves running many tests repeatedly, it is a prime candidate for automation. A robust CI/CD pipeline will run regression tests on every commit.
Scope
Can range from a small set of critical tests (Smoke Tests) to the entire test suite.