A regression test checks that software behavior that worked before still works after a change. It helps catch unintended side effects from a feature, bug fix, configuration or data update, or relevant environment change. Teams can run regression tests manually or automate them; the right scope depends on the change’s risk and the workflows that matter most.
What regression testing means
Regression testing is testing previously tested software after a modification to check that the change has not introduced defects—or exposed defects—in areas that were not meant to change. The ISTQB Glossary definition, presented by ISTQB’s glossary, captures this focus on behavior that had already been tested.
In practical terms, the question is: “After this update, do the important things that used to work still work?” Microsoft Learn describes regression testing as testing after changes or updates to a solution to verify it continues to work as expected and that the change has not caused problems. It can apply to code, configuration, data, and relevant parts of the operating environment—not only newly written code.
A regression test is not a separate level of testing, such as unit, integration, or system testing. It describes the purpose of a test: checking for unintended consequences of a change. A regression check can therefore be performed at different levels, depending on where the affected behavior is best verified.
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Software components and user workflows are connected. A change intended to fix one issue can affect a neighboring feature, an integration, or a process that was not explicitly part of the change. Regression testing provides evidence that selected existing behavior remains sound before the modified software is released.
For example, if a team changes checkout, an illustrative regression scope could include existing checks for payment, discount application, shipping calculations, and order confirmation. The team should test the intended checkout change too, but the regression checks ask whether related behavior still works as before. The specific tests depend on how the application is built and which workflows the change could affect.
Microsoft’s Dynamics 365 implementation guidance gives a similar example: when an update adds order-processing functionality, run tests for key connected business processes and verify their expected outcomes. Regression testing is especially useful before a change enters production, when failures in existing functionality could affect users or business operations.
When to do regression testing
Run regression tests after a change that could affect previously working behavior. Typical triggers include:
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- A new feature or modification to an existing feature.
- A bug fix, alongside a check that the original defect is actually resolved.
- A configuration or data change that may alter other processes.
- An update to a relevant dependency, platform, or environment.
- A release candidate or other change before it is introduced into production.
Not every change requires the same test suite. A small, isolated change may justify targeted checks; a change with broad dependencies or high business impact may call for wider coverage. The team should make that choice based on risk, affected workflows, and the cost of running and maintaining tests.
Regression testing vs. confirmation testing (retesting)
Confirmation testing and regression testing answer different questions, and both may be needed after a bug fix.
| Testing activity | Question it answers | What to run |
|---|---|---|
| Confirmation testing (often called retesting) | Did the fix resolve the defect that caused the original failure? | Repeat the relevant failed test, using the conditions needed to verify the fix. |
| Regression testing | Did the modification cause a failure in other behavior that previously worked? | Run relevant existing tests for potentially affected areas beyond the specific defect. |
ASTQB’s explanation of ISTQB Foundation Level material distinguishes the two by noting that subsequent regression testing checks whether fixes cause failures elsewhere in the test object. In a bug-fix release, first confirming the fix does not replace checking for side effects.
How to choose a practical regression scope
There is no single scope that fits every release. Microsoft Learn describes broad testing, business-impact prioritization, change-focused testing, and combinations of these approaches. A useful selection process is to start with the consequences of failure, then account for what the change touches.
- Protect critical workflows. Identify the user journeys or business processes whose failure would matter most. These are candidates for inclusion even if they are not the code’s most obvious neighbors.
- Cover the changed area. Include tests for the feature, component, or process directly modified. For a fix, keep the confirmation test distinct from checks for other behavior.
- Add nearby dependencies. Consider integrations, data flows, and adjacent workflows that rely on the changed area or share its components.
- Expand according to risk. Broaden the suite when the change has wide reach, failure consequences are high, or earlier test results reveal unexpected effects.
- Review after failures. Use defects and missed impacts to improve future test selection rather than assuming the current suite covers every risk.
| Scope approach | Coverage and effort | Main trade-off |
|---|---|---|
| Broad suite | Tests nearly all relevant processes; generally takes more effort to run and maintain. | Provides wider coverage, but costs more than a focused selection. |
| Business-impact prioritized | Emphasizes mission-critical processes and high-consequence failures. | Uses effort where failure matters most, but does not establish that lower-priority areas are free of regressions. |
| Change-focused | Targets areas affected by the modification, reducing the amount of testing. | Efficient for a well-understood change, but may miss effects outside the selected area. |
| Combined | Pairs critical workflows with directly affected areas and expands where risk warrants. | Balances cost and coverage, but still depends on sound impact analysis. |
Focused testing is not proof that untested parts of the application remain unaffected. Conversely, running everything after every small change can consume time and make tests expensive to maintain. Choose a deliberate balance and revisit it as the application and its risks change.
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Is regression testing manual or automated?
It can be either. A tester can manually repeat checks, or a team can automate tests and run them repeatedly. Manual testing can suit exploratory investigation, unusual cases, or checks that are not yet practical to automate. Automation is particularly useful for important workflows that need recurring, consistent verification.
Microsoft recommends building automation progressively around key business processes. Azure Well-Architected guidance supports integrating tests into CI/CD and scheduling full-suite runs for tests that are too long to run on every commit. A practical arrangement is to run a suitably quick, focused set during frequent development checks and schedule longer coverage separately; the exact cadence depends on the suite and delivery process.
Automated tests do not eliminate the need to choose good coverage or maintain reliable checks. A test that does not represent a real expected behavior can create false confidence, while a brittle test may require ongoing repair. Keep expected outcomes clear and update tests when intended product behavior changes.
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How regression testing fits into a release
- Understand the change. Record what changed and what behavior is intended to be different.
- Identify impact and risk. Map direct dependencies and the user or business workflows that could be affected.
- Run confirmation checks where relevant. For a bug fix, verify the original failure no longer occurs.
- Run the selected regression suite. Check previously working behavior at the test levels that fit the affected components.
- Assess results before release. Investigate failures, determine whether they are regressions or unrelated test issues, and make the release decision using the team’s quality criteria.
- Improve coverage from what you learn. Add or refine checks when a real failure reveals a gap in the suite.
Common mistakes to avoid
- Testing only the new feature. That can confirm the intended change while leaving side effects in existing workflows unchecked.
- Calling a fix check regression testing. Repeating the failed test confirms the fix; regression testing looks for other affected behavior.
- Assuming a small code change has small impact. Shared components, configuration, and data can connect apparently separate workflows.
- Assuming a focused suite proves broad safety. Areas outside the chosen scope remain less checked.
- Automating everything without prioritization. Maintenance and execution effort are part of the scope decision; prioritize recurring, important checks.
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Frequently Asked Questions
Is regression testing the same as end-to-end testing?
No. Regression testing describes why a test is run—checking for unintended effects after a change—while end-to-end testing describes a test scope or approach that follows behavior across a complete workflow. An end-to-end test can be part of a regression suite.
Does every software change need the full regression suite?
No. Choose scope according to impact and risk. A full suite offers broader coverage but costs more to run and maintain; a focused suite is more efficient but leaves untested areas less checked.
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