Regression Testing

Regression testing re-runs previously passing tests after a code change, confirming that existing functionality hasn't been accidentally broken by new work.

Why Regressions Happen

A "regression" is a defect introduced into functionality that previously worked correctly, usually as an unintended side effect of a seemingly unrelated code change. As a codebase grows, the number of ways a small change can ripple outward and break something distant increases significantly.

Building a Regression Suite

A regression suite is a curated set of tests, typically automated, covering the application's core functionality, run after every meaningful change to catch regressions immediately rather than discovering them after release.

Common Mistakes

• Skipping regression testing for "small" changes, which are often exactly the changes that produce unexpected side effects.
• Letting a regression suite grow stale, never adding new tests as new features and edge cases are discovered.
• Running regression tests manually every time when automation would make them far faster and more consistent to execute.
• Removing a regression test simply because it's inconvenient, rather than fixing the underlying issue it's catching.