Regression testing

Regression testing is re-running existing tests after a code change to confirm that features that worked before still work. It catches bugs that a new change accidentally introduces in other parts of the application.

When to run regression tests

• After every bug fix or new feature, before merging.
• Before each release, as a full or risk-based suite.
• After upgrades to libraries, browsers or infrastructure.

Full vs selective regression

A full regression run executes the whole suite. A selective run picks the tests related to the changed code or the highest-risk features. Teams often run a fast selective set on every pull request and the full suite nightly or before a release.

Why automate it

Regression suites grow with every release, so running them by hand gets slow and error-prone. Automated UI, API and unit tests in a CI pipeline give feedback in minutes. Keep the suite healthy by fixing or removing flaky tests, because a suite people stop trusting stops catching regressions.

Read the full guide: GitHub Actions for Test Automation 2026 — Complete SDET Guide