What is Regression Testing?
Regression testing verifies that previously working functionality still works after code changes.
Regression testing verifies that previously working functionality still works after code changes. It catches "regressions" — bugs introduced by new code that break existing behavior. Regression testing is the safety net that enables continuous deployment.
Approaches: Automated regression suite (run the full test suite on every deployment), Selective regression (run only tests affected by changed code — tools like Jest --changedSince), Visual regression (screenshot comparison to catch UI changes — Percy, Chromatic), and Smoke testing (quick subset of critical tests run immediately after deployment).
Regression testing ROI: Without regression tests, every deployment requires manual verification of everything that could break. With regression tests, verification is automated, allowing daily (or hourly) deployments with confidence.
Why It Matters
Every line of code you change could break something else. Regression testing automates the verification that "everything still works." Without it, deployment speed is limited by manual testing capacity.
Frequently Asked Questions
What is regression testing?
Testing that verifies existing functionality still works after code changes. Catches "regressions" — new code breaking old behavior. The safety net that enables continuous deployment.
How long should regression tests take?
Target: < 15 minutes for the full suite. If longer, you need test optimization (parallelization, selective testing, faster infrastructure). Slow tests = slow deployments = slow feedback.
Related Terms
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