Ln 42 Acceptance Test Builder Skill for Claude

Acceptance Test Builder

Goal: Create executable evidence that stated requirements work through the boundary users or external systems observe. Modify only the approved test and test-documentation scope. If a test exposes a product defect, preserve the evidence and report it instead of repairing production code.

Execution contract: Treat the ordered checkbox workflow below as this skill's Definition of Done. Work through every item in order, and mark it complete only when its action and required evidence are complete. N/A, skipped, unavailable, or delegated items remain incomplete.

Before returning, apply this skill's verdict, decision, and approval rules to every incomplete item and prepend Checklist: X/Y complete<br>Incomplete: None | section/item — reason; outcome impact; exact next action; list every incomplete item.

Tool Routing

| Need | Preferred tool | Use it when | Fallback |

|---|---|---|---|

| Workspace safety | Git status, diff, repository instructions, and branch or worktree inspection | Always before editing | Stop when user changes cannot be separated safely |

| Existing test conventions | File listing, search, manifests, runner configuration, CI, and focused reads | Selecting the project-native runner, layout, fixtures, and commands | Follow the nearest maintained test pattern |

| Behavior and wiring | Language server or host-native code intelligence | Locating observable entrypoints, registration, consumers, and state boundaries | Narrow search plus direct inspection |

| Test implementation | Native editing tools and project generators | Creating tests, fixtures, helpers, and narrowly required test documentation | Minimal project-consistent files; never hand-edit generated state |

| Observable execution | Repository-defined shell commands, browser, API client, CLI, or disposable integration environment | Proving UI, protocol, command, or durable state outcomes | Return INCOMPLETE with the exact missing check |

| External contract | Official version-matched documentation or specification | Expected behavior depends on a current external API or standard | Mark it UNVERIFIED; do not encode a guessed oracle |

Never run acceptance tests against production or an unapproved external target. Do not deploy, publish, migrate shared data, rotate credentials, or accept changed output merely to make a test pass.

Evidence Rules

• Derive expected behavior from requirements, public contracts, examples, invariants, or an independent reference; never from the implementation calculation being tested.
• Prefer a terminal durable or user-visible outcome over an intermediate status, mock call, log line, or internal method result.
• Use golden files or snapshots only for deterministic, reviewable contracts. Updating expected output is a specification change, not test verification.
• Make setup, data allocation, execution, cleanup, and rerun behavior reproducible; preserve the first failure before retries or cleanup obscure it.
• A passing command proves only the environment and scenarios it actually exercised. State every excluded cell and unavailable boundary.

Checklist

1. Establish the Change Boundary

• [ ] Resolve the requirements, acceptance criteria, actor, protected outcome, observable contract, explicit non-goals, allowed test paths, and allowed test-documentation paths; label inferred experience qualities as assumptions.
• [ ] Read applicable repository instructions and inspect Git state, untracked files, generated areas, and existing user changes before editing.
• [ ] Detect the project-native runner, directory layout, naming, fixtures, setup, cleanup, environment configuration, and CI invocation.
• [ ] Map each requirement to the boundary that can prove it: UI, API, CLI, message, integration, file, or durable state.
• [ ] Identify credentials, services, accounts, ports, devices, browsers, datasets, and destructive effects required by the scenarios.
• [ ] Return BLOCKED before editing when no safe target, reliable expected contract, or separable workspace exists.

2. Design Reproducible Acceptance Evidence

• [ ] Define the protected outcome, defect class, setup, action, terminal outcome, independent oracle, expected evidence, and cleanup for every requirement.
• [ ] Use the lowest production-shaped boundary that still proves the requirement; do not replace acceptance evidence with a unit-level implementation check or create acceptance coverage for an internal detail absent from the observable contract.
• [ ] Include invalid, authorization, boundary, partial-failure, retry, idempotency, recovery, and compatibility behavior only when it can materially change the protected outcome.
• [ ] Allocate unique or namespaced test data and control clock, randomness, locale, ordering, and concurrency where they affect reproducibility.
• [ ] Use real dependencies or approved emulators when mocks would bypass the behavior under acceptance; pin versions and verify readiness and reset behavior.
• [ ] For deterministic output, derive golden or diff expectations from an independent contract and keep the artifact small enough to review.
• [ ] For nondeterministic output, assert stable invariants and semantic fields instead of normalizing away failures or snapshotting noise.

3. Implement within Test Scope

• [ ] Create or update tests in the existing project layout with behavioral names and failure messages that identify the violated requirement, protected outcome, and detected defect.
• [ ] Reuse maintained fixtures and helpers only when their defaults and side effects remain visible; avoid a new abstraction for one scenario.
• [ ] Make setup fail fast on missing prerequisites and make cleanup safe after success, assertion failure, timeout, cancellation, or partial setup.
• [ ] Keep tests rerunnable and idempotent; do not depend on execution order or silently reuse state from a previous run.
• [ ] Add the narrowest required test documentation only when contributors otherwise cannot configure, run, interpret, or clean up the new evidence.
• [ ] Do not edit production code, weaken assertions, broaden timeouts without evidence, skip failing cases, or regenerate expected artifacts to obtain a pass.
• [ ] Inspect the diff for unrelated formatting, generated churn, secrets, environment-specific paths, and changes outside the approved scope.

4. Execute and Preserve Evidence

• [ ] Run the smallest new scenario first, then the relevant suite and required repository gate when available.
• [ ] Record the exact command, working directory, environment class, target, versions, exit status, duration, and artifact locations.
• [ ] Preserve the first failing output, seed, order, request, response, screenshot, diff, or durable state needed to reproduce the defect.
• [ ] Distinguish product failure, test defect, environment failure, unavailable dependency, and flaky evidence before changing the test.
• [ ] If the test exposes a product defect, stop modifying the implementation, retain the failing acceptance evidence, and report the smallest reproduction.
• [ ] Verify cleanup and rerun at least the affected scenario when state ownership or idempotency is material.
• [ ] Avoid retries unless they diagnose nondeterminism; a retry must not convert the initial failure into a silent pass.

5. Finalize without Overclaiming

• [ ] Map every requirement and protected outcome to its test path, command, oracle, and result as PASS, FAIL, or UNPROVEN.
• [ ] Use COMPLETE when the requested tests are created and all required acceptance evidence executes to a recorded PASS or FAIL; this verdict describes evidence completion, not product correctness.
• [ ] Use INCOMPLETE when tests are created but an environment, dependency, or interrupted run prevents complete execution; state the exact missing check.
• [ ] Use BLOCKED when tests cannot be created safely, requirements lack a reliable oracle, or the workspace cannot be protected.
• [ ] Return created and changed test files, commands, evidence, cleanup result, limitations, product defects, and residual risks.

Output Contract

# Acceptance Test Build

**Verdict:** COMPLETE | INCOMPLETE | BLOCKED

## Scope and environment
- Requirements and approved paths
- Runner, boundary, target, and prerequisites

## Requirements matrix
| Protected outcome | Requirement | Test | Oracle | Command | Result |
|---|---|---|---|---|---|
| ... | ... | ... | ... | ... | PASS / FAIL / UNPROVEN |

## Changes and evidence
- Created or changed test and documentation files
- Exact commands, outputs, and evidence artifacts
- Product defects preserved without repair

## Cleanup, limitations, and residual risks
State cleanup, unavailable environments, excluded cells, and remaining evidence needs.