Definition
Regression testing is the practice of re-testing existing functionality after code changes to ensure nothing that previously worked has broken. When engineers add a feature, fix a bug, or refactor code, they may unintentionally affect other parts of the system. Regression tests catch these unintended side effects before they reach production.
The term "regression" means the software has regressed -- gone backward from a working state to a broken one. A classic example: an engineer optimizes the database query for the user profile page and inadvertently breaks the password reset flow because both share a database function. Without regression tests, this bug ships to production and users cannot reset their passwords.
Regression testing can be manual (a QA team clicks through test cases) or automated (a test suite runs on every commit). Most modern engineering teams automate the majority of regression tests and run them as part of their CI/CD pipeline. GitHub, for example, runs over 100,000 automated tests on every pull request.
Why It Matters for Product Managers
Regression bugs erode user trust faster than missing features. Users tolerate a product that lacks a feature they want. They do not tolerate a product where features they depend on randomly break. A Stripe customer whose payment processing silently fails will churn faster than a Stripe customer who wishes the dashboard had better filtering.
For PMs, regression testing is the guardrail that enables speed. Without it, every release is a gamble -- the team ships a new feature and hopes nothing else broke. With it, the team ships with confidence because automated tests have verified that critical paths still work. This is what makes continuous delivery possible.
PMs should care about regression test coverage for the same reason they care about product quality: it directly affects user experience, incident frequency, and the team's ability to iterate quickly. Teams with weak regression testing spend more time firefighting production bugs and less time building new features. The DORA research found that elite-performing teams have change failure rates below 5%, largely because they invest in automated testing.
How It Works in Practice
Identify critical paths -- Map the user flows that must never break: account creation, login, core workflow completion, checkout, billing, data export. These are your regression test priorities. At Shopify, the checkout flow has thousands of automated tests because any regression there directly costs merchants revenue.
Automate at multiple levels -- Build regression tests at three layers: unit tests (fast, test individual functions), integration tests (test how components work together), and end-to-end tests (test full user flows in a browser). The "testing pyramid" suggests many unit tests, fewer integration tests, and even fewer E2E tests.
Run on every commit -- Integrate regression tests into the CI/CD pipeline so they execute automatically on every pull request. Engineers see test results before their code is merged. A failing regression test blocks the merge until the issue is fixed.
Maintain the suite -- Regression test suites grow over time and need maintenance. Flaky tests (tests that pass and fail randomly) must be fixed or removed immediately, because they train engineers to ignore test failures. Slow tests should be optimized or moved to a nightly run.
Supplement with manual testing -- Automated tests cannot catch everything. Visual regressions (a button shifting 50 pixels), subtle UX issues (a flow that technically works but feels confusing), and edge cases in complex interactions benefit from human review. Some teams run manual regression on release candidates for major launches.
Common Pitfalls
No regression tests for the critical path. If your signup flow, core workflow, and billing system do not have automated regression tests, you are depending on luck every time you deploy. Prioritize these first.
Test suite so slow nobody runs it. A regression suite that takes 2 hours discourages engineers from running it locally and slows down the CI pipeline. Keep the main suite under 15 minutes. Move expensive tests to a nightly or pre-release run.
Testing everything at the E2E level. End-to-end tests (Selenium, Playwright, Cypress) are the most realistic but also the slowest and most brittle. Test business logic with fast unit tests. Reserve E2E tests for critical user flows.
Treating regression testing as purely QA's job. In modern development, engineers write and maintain regression tests as part of their definition of done. A dedicated QA team can supplement with exploratory testing, but the engineering team owns the automated suite.
Related Concepts
Definition of Done (DoD) -- often includes "regression tests passing" as a requirement before work is considered complete
Continuous Delivery -- relies on automated regression tests to confirm that software is always safe to deploy
Technical Debt -- codebases with high technical debt are more prone to regressions because tightly coupled code means changes in one area break anotherExplore More PM Terms
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