TDD

Use this skill only for one complete, human-accepted bounded issue. The issue is the scope boundary; do not turn an implementation request into planning, backlog generation, architecture work, or unrelated cleanup.

Entry Gate

Before inspecting project code, verify that the supplied issue artifact contains:

• one issue ID and one observable outcome;
• explicit acceptance criteria, layers, modules, tests, constraints, and non-goals;
• known project commands for every applicable fast check;
• no unresolved human decision, unsafe HITL work, credential requirement, irreversible operation, or unknown command.

Reject or block the issue when any item is absent. TYPE: hitl, STATUS: blocked, COMMANDS: UNKNOWN, unresolved HITL, or unsafe work is never implementable by this agent. Do not infer missing details.

Relevant Surface

Discover project-local instructions and the declared commands first. Inspect only the modules, tests, migration files, and configuration needed by the issue. Treat unrelated existing changes as read-only and preserve them. Do not add public modules or cross boundaries not named by the issue; stop and report a boundary conflict instead of expanding scope.

Red, Green, Refactor

For behavior that can be tested:

1. Red: add or strengthen the smallest acceptance-focused test, run the declared focused test command, and record a genuine non-zero result caused by the missing behavior. A syntax error, missing dependency, or broken setup is not red evidence.
2. Green: make the smallest implementation that satisfies the acceptance criteria, rerun the same test, and record the zero exit result.
3. Refactor: inspect the diff and simplify names, duplication, or structure without changing behavior; rerun the affected test and fast checks, recording the final result. Refactor evidence may be “no safe refactor needed” only when the diff review and final checks are recorded.

For migrations, red must be a failing migration/application assertion or rehearsal against a disposable database, green must show the migration and affected behavior passing, and refactor must rerun the migration checks after mechanical cleanup. Never run against production data.

If behavior is genuinely not executable-testable, state why, name the substitute evidence, and obtain the issue's explicit human gate. Do not claim TDD completion for unsafe or visual-taste-dependent work.

Checks and Evidence

Run the project's declared fast checks sequentially, not invented commands. Stop on the first blocking failure. Record each command exactly, cwd, command-scoped environment and inherited environment provenance, start/end or duration, exit code, and complete log or artifact path. FAIL blocks completion; BLOCKED and UNAVAILABLE require owner and residual-risk records.

Return an implementation-result artifact, not a completion assertion, containing:

• issue ID and outcome;
• files changed and tests added;
• red, green, and refactor evidence;
• every check's command, cwd, environment, duration, exit code, result, and complete evidence path;
• preserved unrelated changes and module-boundary notes;
• unresolved risks, unavailable checks, and any follow-up issue.

Implementation, project checks, independent review, and human acceptance are separate responsibilities. This skill never declares independent verification.