Regression Testing: Engineering for Vibe Coders
Most bugs do not come from new features.
They come from old features breaking.
Regression testing is how you protect what already works while you keep building. It is not about perfection or test coverage numbers. It is about confidence.
For vibe coders moving fast with AI tools, regression testing is often skipped because everything looks fine right now. The problem is that systems change faster than memory.
What Regression Testing Is
Regression testing checks that existing behavior still works after changes are made.
It answers simple but critical questions:
- Did this change break something that used to work?
- Did a fix introduce a new bug somewhere else?
- Did refactoring change behavior accidentally?
Regression tests can be automated or manual, but they must be repeatable.
🟢 Pre-prototype habit:
Write down the behaviors that must never change, even as features evolve.
Why Regression Testing Matters for Vibe Coders
AI coding tools are great at generating new code.
They are not great at understanding everything the system already does.
That means changes are often broad and confident, but not careful.
Without regression tests:
- Small tweaks cause surprising breakage
- Bugs reappear weeks later
- Fear replaces momentum
Regression testing lets you move fast without relying on memory.
🟢 Pre-prototype habit:
Identify which workflows would be most embarrassing or costly to break in a demo or launch.
What Should Be Covered by Regression Tests
Not everything needs regression tests.
Focus on:
- Core user flows
- Critical business rules
- Security and permissions
- Data integrity checks
- Integrations with external systems
If a feature matters enough to keep, it matters enough to protect.
🟢 Pre-prototype habit:
List the top five actions users will perform and mark which ones must always work.
Automated vs Manual Regression Testing
Manual regression testing does not scale.
Automated regression testing does.
Manual testing works early, but it relies on people remembering what to test. Automated tests remember for you.
Good automated regression tests:
- Are stable
- Are deterministic
- Check behavior, not implementation details
The goal is trust, not test volume.
🟢 Pre-prototype habit:
Decide which behaviors should eventually be locked in with automated tests.
Regression Testing and Refactoring
Refactoring without regression tests is gambling.
When tests exist, refactoring becomes safer and faster because you can change structure without changing behavior.
Regression tests give you permission to improve code instead of freezing it.
🟢 Pre-prototype habit:
Assume you will rewrite parts of your app later and decide how you will know nothing broke.
Regression Testing as a Feedback Loop
Regression testing is not a one time task.
Each bug you fix should raise a question:
- Should this bug ever be allowed to happen again?
If the answer is no, it deserves a regression test.
Over time, your test suite becomes a history of lessons learned.
🟢 Pre-prototype habit:
Plan to turn painful bugs into permanent protections rather than temporary fixes.
Regression Testing Is About Confidence
Regression testing does not slow you down.
It removes fear.
When vibe coders skip regression testing, progress feels fast until it suddenly stops. When regression testing exists, change becomes routine instead of risky.
Build fast.
Protect what works.
That is the real purpose of regression testing.
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