tldr: Regression testing re-runs existing tests after a change to confirm nothing that used to work is now broken. It is the core of continuous quality, and it is where most QA time goes. The hard part is not running it, but keeping the suite current and fast.
What regression testing is and when to run it
A regression is a feature that used to work and now does not. Regression testing catches those by re-running known-good tests against new code.
Run it on every meaningful change. Before a merge, before a release, after a dependency bump, after a hotfix. The whole value is catching the break that a small, unrelated change caused somewhere you were not looking.
Manual vs automated
Manual regression works for a handful of flows. It stops scaling the moment your test count passes what a person can re-run on every release without burning out or cutting corners.
Automated regression is the only model that holds up under frequent deploys. The cost moves from running the tests to maintaining them as the app changes, which is the real long-term expense.
Test selection and prioritization
You rarely need to run everything on every commit. Prioritize by risk: critical user paths, recently changed areas, and historically flaky or bug-prone modules first.
Risk-based selection keeps feedback fast without giving up coverage where it counts. A full suite can run nightly while a focused subset gates each pull request.
Tooling
Regression suites run on frameworks like Playwright, Selenium, or Cypress, wired into CI so they fire on every change. The tooling is the easy part.
The hard part is maintenance. Locators drift, flows change, and a neglected suite turns red for the wrong reasons until people stop trusting it. Self-healing test automation and disciplined test maintenance are what keep a regression suite alive.
Bug0 and continuous regression coverage
Regression is the core product problem for any team shipping often. Bug0 delivers continuous regression coverage as a service: an engineer plans the suite, builds it on its AI engine, and the engine runs and self-heals it on every deploy with every result verified. For a contrasting take on the economics, the blog post on the regression testing ROI trap argues a related point from the cost angle.
See also confirmation testing and baseline testing for the adjacent concepts.
FAQs
What is the difference between regression and confirmation testing?
Confirmation testing checks that a specific fix works. Regression testing checks that the fix, or any other change, did not break something else.
How often should regression tests run?
On every meaningful change for a prioritized subset, and on a full schedule (often nightly) for the complete suite.
Can you do regression testing manually?
For a small app, yes. It stops being practical once the suite is larger than a person can reliably re-run on every release.
Why does regression testing get so expensive?
Maintenance, not execution. Keeping tests current as the UI and flows change is the dominant cost. Self-healing and managed services like Bug0 exist to absorb it.