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Grok
Grok Bot+18 agentsBug to Regression Test Builder
Turn a real bug into a minimal regression test that proves the fix and prevents recurrence.
Free
Bug to Regression Test Builder
Example session with this skill installed
Turn this bug into the smallest regression test that proves the fix:
Bug: normalizeUser() crashes when aliases is missing.
Expected behavior: missing aliases should be treated as an empty list.
Current code
function normalizeUser(user) {
return {
...user,
aliases: user.aliases.map(a => a.trim())
}
}
- Read your context and instructions
- Compiled the bug to regression
BUG → REGRESSION TEST
1. Bug contract
Expected: normalizeUser() should accept a user with no aliases and return aliases: [].
Observed: It throws while calling .map() on undefined.
Minimal trigger: { id: "u1", aliases: undefined }.
2. Evidence
Observed
aliasesmay beundefined.- Current implementation calls
.map()directly. - User states missing aliases should be treated as an empty list.
Inferred
- The likely fix is to default
aliasesto[].
Unknown
- Whether
nullshould be treated the same way.
3. Regression target
Behavior to protect: Missing aliases do not crash normalization and produce an empty array.
Why this is the right target: It protects the user-visible contract rather than one implementation.
4. Minimal reproduction
Call normalizeUser({ id: "u1", aliases: undefined }).
5. Regression test
it("treats missing aliases as an empty list", () => {
const result = normalizeUser({ id: "u1", aliases: undefined });
expect(result.aliases).toEqual([]);
});
6. Before / after proof
Before fix: Test throws before reaching the assertion.
After fix: Test passes and returns aliases: [].
7. Binding check
Future implementations must preserve the no-crash + empty-list behavior for missing aliases.
8. Maintenance cost
Low. No external dependencies, mocks, or environment setup.
9. What would invalidate this test
- Product contract changes so missing aliases should be rejected.
- Repository schema guarantees aliases can never be missing.
10. Next action
Add the test first, confirm it fails on the current code, then implement the smallest fix.
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About this skill
From bug report to proof the fix will hold.
Most generated tests cover the happy path. This skill starts from a real bug, failed run, stack trace, or fix diff and builds the smallest regression test that stays tied to the actual failure.
It does not guess a root cause just to produce code. It separates what the evidence proves from what is still inferred, reconstructs the minimal trigger, defines the behavior that must be protected, and creates a test that should fail before the fix and pass after it.
What it does
-
Reconstructs the expected behavior, observed failure, and minimal trigger.
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Separates direct evidence from assumptions about the cause.
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Builds the smallest safe reproduction before generating the test.
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Creates a focused regression test instead of a broad generic test suite.
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Checks that the test proves the correction rather than merely matching the current implementation.
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Identifies what must remain different on future comparable runs for the fix to count as real.
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Flags brittle fixtures, expensive setup, false positives, and tests that shift maintenance burden into CI.
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States what evidence would invalidate the proposed regression test.
Use it when
- a bug was fixed and you need permanent coverage
- an AI agent failed and you want a reusable regression case
- a stack trace needs to become a failing test
- a bug report is too vague to turn directly into code
- you need a minimal repro before changing implementation
- you want to verify that a patch actually fixes the reported behavior
What you get
- Bug contract
- Observed / inferred / unknown evidence
- Minimal reproduction
- Regression target
- Runnable test or precise test plan
- Before / after proof
- Binding check
- Maintenance-cost check
- What would invalidate the test
- Next action
Why it is different
A passing test is not automatically a good regression test. This skill asks whether the test is attached to the real failure, whether the expected behavior is actually supported, and whether the same class of failure would be caught next time.
Known limitations
The skill cannot infer an intended product contract that is absent from the bug report, code, specification, or user context. When the behavior is genuinely ambiguous, it identifies the missing decision instead of inventing one.
How to install
Works the same in every agent - Claude, Cursor, Codex, Copilot and 20+ more.
- 1
Download the ZIP
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- 2
Unzip into your skills folder
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- 3
Ask your agent to use it
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