reproduce-bug

SKILL.md

Bug Reproduction Framework

Given a Linear ticket context ($ARGUMENTS), systematically reproduce the bug
with a failing regression test.

Step 1: Parse Signals

Extract the following from the provided ticket context:

Error message / stack trace (if provided)

Reproduction steps (if provided)

Workflow JSON (if attached)

Affected area (node, execution engine, editor, API, config, etc.)

Version where it broke / last working version

Step 2: Route to Test Strategy

Based on the affected area, pick the test layer and pattern:

Area
Test Layer
Pattern
Key Location

Node operation
Jest unit
NodeTestHarness + nock
packages/nodes-base/nodes/*/test/

Node credential
Jest unit
jest-mock-extended
packages/nodes-base/nodes/*/test/

Trigger webhook
Jest unit
mock IHookFunctions + jest.mock GenericFunctions
packages/nodes-base/nodes/*/test/

Binary data
Jest unit
NodeTestHarness assertBinaryData
packages/core/nodes-testing/

Execution engine
Jest integration
WorkflowRunner + DI container
packages/cli/src/__tests__/

CLI / API
Jest integration
setupTestServer + supertest
packages/cli/test/integration/

Config
Jest unit
GlobalConfig + Container
packages/@n8n/config/src/__tests__/

Editor UI
Vitest
Vue Test Utils + Pinia
packages/frontend/editor-ui/src/**/__tests__/

E2E / Canvas
Playwright
Test containers + composables
packages/testing/playwright/

Step 3: Locate Source Files

Find the source code for the affected area:

Search for the node/service/component mentioned in the ticket

Find the GenericFunctions file (common bug location for nodes)

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/ 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 node/service 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 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 from the package directory (e.g., cd packages/nodes-base && pnpm test <file>).

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 can't 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.ts
XX-YY
Description of the problem

Failing Test

path/to/test/file.test.ts — 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)

Run tests from the package directory (e.g., pushd packages/nodes-base && pnpm test <file> && popd)

Always redirect build output: pnpm build > build.log 2>&1

DO NOT look at existing fix PRs — the goal is to reproduce from signals alone