Reproduce bug
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npx -y skills add yunseo-kim/agent-toolbox --skill reproduce-bugAssembled from the repository path, not quoted from the project. Check it against their README if it does not work.
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Systematically reproduce a bug from a ticket or report with a failing regression test, using a structured hypothesis-driven methodology.
The file declares its own license as Sustainable Use License 1.0. That is the author’s claim about this one file, and it is not the same thing as the license GitHub reports for the repository, which is listed with the other numbers below.
SKILL.md
4.9 KB, as published. Nobody here has run it
Bug Reproduction Framework
Given a bug report or ticket context ($ARGUMENTS), systematically reproduce the bug with a failing regression test.
Step 1: Parse Signals
Extract the following from the provided ticket/report context:
- Error message / stack trace (if provided)
- Reproduction steps (if provided)
- Sample data or configuration (if attached)
- Affected area (module, component, service, API, etc.)
- Version where it broke / last working version
Step 2: Route to Test Strategy
Based on the affected area, pick the appropriate test layer and pattern:
| Area | Test Layer | Approach |
|---|---|---|
| Business logic / service | Unit test | Mock dependencies, test pure logic |
| API endpoint | Integration test | HTTP client + test server |
| Database operation | Integration test | Test database + fixtures |
| UI component | Component test | Render + simulate interaction |
| CLI command | Integration test | Spawn process + assert output |
| Configuration | Unit test | Load config + validate values |
| End-to-end flow | E2E test | Full stack + browser/client automation |
Adapt the test layer to your project's testing infrastructure. Look for existing test patterns in the codebase and follow them.
Step 3: Locate Source Files
Find the source code for the affected area:
- Search for the module/service/component mentioned in the report
- Find shared utility files (common location for bugs)
- Check for existing test files in the same area
- Look at recent git history on affected files (
git log --oneline -10 -- <path>)
Step 4: Trace the Code Path
Read the source code and trace the execution path that triggers the bug:
- Follow the call chain from entry point to the failure
- Identify the specific line(s) where the bug manifests
- Note any error handling (or lack thereof) around the bug
Step 5: Form Hypothesis
State a clear, testable hypothesis:
- "When [input/condition], the code does [wrong thing] because [root cause]"
- Identify the exact line(s) that need to change
- Predict what the test output will show
Step 6: Find Test Patterns
Look for existing tests in the same area:
- Check
test/or__tests__/directories near the affected code - Identify which mock/setup patterns they use
- Use the same patterns for consistency
- If no tests exist, find the closest similar module's tests as a template
Step 7: Write Failing Test
Write a regression test that:
- Uses the patterns found in Step 6
- Targets the specific hypothesis from Step 5
- Includes a comment referencing the ticket/issue ID
- Asserts the CORRECT behavior (test will fail on current code)
- Also includes a "happy path" test to prove the setup works
Step 8: Run and Score
Run the test using the project's test runner.
Classify the result:
| Confidence | Criteria | Output |
|---|---|---|
| CONFIRMED | Test fails consistently, failure matches hypothesis | Reproduction Report |
| LIKELY | Test fails but failure mode differs slightly | Report + caveat |
| UNCONFIRMED | Cannot trigger the failure | Report: what was tried |
| SKIPPED | Hit a hard bailout trigger | Report: why skipped |
| ALREADY_FIXED | Bug no longer reproduces on current code | Report: when fixed |
Step 9: Iterate or Bail
If UNCONFIRMED after first attempt:
- Revisit hypothesis -- re-read the code path
- Try a different test approach or layer
- Maximum 3 attempts before declaring UNCONFIRMED
Hard bailout triggers (stop immediately):
- Requires real third-party API credentials
- Race condition / timing-dependent
- Requires specific cloud/enterprise infrastructure
- Requires manual UI interaction that cannot be scripted
Output: Reproduction Report
Present findings in this format:
Ticket: [ID] -- [title] Confidence: [CONFIRMED | LIKELY | UNCONFIRMED | SKIPPED | ALREADY_FIXED]
Root Cause
[1-2 sentences explaining the bug mechanism]
Location
| File | Lines | Issue |
|---|---|---|
path/to/file | XX-YY | Description of the problem |
Failing Test
path/to/test/file -- X/Y tests fail:
test name-- [failure description]
Fix Hint
[Pseudocode or description of the fix approach]
Important
- DO NOT fix the bug -- only reproduce it with a failing test
- Leave test files in place as evidence (don't commit unless asked)
- Always redirect build output:
command > build.log 2>&1 - DO NOT look at existing fix PRs -- the goal is to reproduce from signals alone