QA Fundamentals
Regression Bug
A bug introduced by a code change that breaks previously working functionality.
Full definition
A regression bug is a defect that appears in previously working functionality after a code change — a new feature, bug fix, or configuration change.
Why regressions happen:
- Code changes have unintended side effects
- Dependencies between modules aren't fully understood
- Insufficient test coverage in affected areas
- Configuration changes impacting other features
Preventing regressions:
- Comprehensive automated regression test suite
- CI/CD running tests on every commit
- Good code architecture (loose coupling)
- Code reviews checking for side effects
- Feature flags for gradual rollouts
Regression bugs are especially frustrating because they break user trust — something that used to work suddenly doesn't. This is why regression testing (and especially automated regression testing) is so important.
Every bug fix should include a regression test that specifically checks for that bug. This prevents the same bug from reappearing in the future.