Regression Testing in CI/CD Pipelines

Continuous integration and delivery pipelines are most effective when they include automated regression checks. Running key tests on every change reduces the window in which defects can slip through. However, simply adding all tests to the pipeline can make builds slow and unstable. The challenge is to design regression runs that fit the pipeline while still providing strong feedback.

Placing Regression Tests in CI/CD #

Many teams use a layered approach in CI/CD. Fast unit and component tests run first, followed by a small smoke regression suite on every merge. A larger core regression suite might run on a schedule, on release branches, or before deployment to production. Each layer is tuned to the time and stability requirements of that stage in the pipeline.

# Example CI job snippet (conceptual)

jobs:
  smoke-regression:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - name: Install dependencies
        run: npm ci
      - name: Run UI smoke regression
        run: npm test -- --group=regression:smoke

  nightly-regression:
    runs-on: ubuntu-latest
    schedule:
      - cron: "0 2 * * *"
    steps:
      - uses: actions/checkout@v4
      - name: Run extended regression suite
        run: npm test -- --group=regression:core

Another important aspect is feedback visibility. Pipeline results should make it easy to see which regression tests failed, what area they belong to, and whether the failure is new or known. Good reporting shortens the time from failure to fix.

Handling Flaky Regression Tests #

Flaky tests that sometimes pass and sometimes fail are especially damaging inside pipelines. When a regression test is flaky, treat that as a defect in the test or environment. Quarantine flaky tests, investigate the root cause, and only return them to the main suite when they are stable. This keeps the pipeline trustworthy.

Common Mistakes #

Mistake 1 — Pushing the entire regression suite into a single pipeline job #

This often leads to very long build times and unstable feedback.

❌ Wrong: Running thousands of UI tests on every pull request regardless of risk.

✅ Correct: Layer regression checks so quick, targeted suites run frequently and deeper suites run at appropriate times.

Mistake 2 — Ignoring flaky tests instead of fixing them #

Flaky tests erode confidence in the pipeline and slow teams down.

❌ Wrong: Re-running pipelines until tests happen to pass without investigating why they failed.

✅ Correct: Track flaky tests, treat them as issues, and stabilise or redesign them.