---
name: tdd
description: The test-first gate. Routed to by /feature (after the spec is approved), /fix, and /refactor before any implementation code is written. Six gated phases — obligation scan, red, green, obligation verify, coverage, lint. No feature code exists before Phase 1 clears; nothing reaches commit-gate until all six are green.
disable-model-invocation: true
---

# tdd

Test-first, or it does not ship. Routed to by `/feature` (after spec approval), `/fix`, and `/refactor`.

## Pre-flight

Read these, or STOP and surface the gap — never guess a command or a threshold:

- `{{PROJECT_DIR}}/.codearbiter/CONTEXT.md` — the `stage:` frontmatter (the maturity value) and project context.
- `{{PROJECT_DIR}}/.codearbiter/tech-stack.md` — test, coverage, and lint invocations; file layout; mock patterns.
- `{{PROJECT_DIR}}/.codearbiter/coding-standards.md` — style, structure, naming. Required for Phase 3.
- `{{PROJECT_DIR}}/.codearbiter/specs/<slug>.md` — the approved spec, when `/feature` produced one. It is the primary obligation source.
- `{{PROJECT_DIR}}/.codearbiter/security-controls.md` — only when the change touches a security boundary (auth, crypto, secrets, a trust boundary). Optional; absent on most changes.
- `{{PROJECT_DIR}}/.codearbiter/code-map.md` — if present, a coarse concern→path→role map to orient before writing tests and code. Absent is fine — it is read-on-demand, populated by context-creation or commit-gate heal.

## Phase 1 — Obligation scan · gate: BLOCK

An **obligation** is one verifiable claim about the change: (a) a unique ID, (b) a source citation,
(c) a status. Status moves `OPEN → MAPPED → COVERED`; an obligation Phase 4 cannot tie to a passing
test is `MISSING`. "We should test X" is not an obligation.

Derive every obligation before any code is written, and record each as `ID · source · OPEN`:

- **Spec** — one obligation per acceptance criterion in the approved spec.
- **Contract** — API and input-validation invariants, error responses, boundary conditions.
- **Security** — only when `security-controls.md` applies: the assertion that the security-relevant boundary holds.

Gate: the obligation list is complete. **Auto-pass** when every obligation maps one-to-one onto the
acceptance criteria of an already-approved spec (full-lane spec or small-lane mini-spec) — the user
approved that list once; do not re-ask. **User review is required** only for obligations derived
BEYOND the spec (Contract and Security rows): surface just those additions, not the whole list.
Under `/sprint`, spec-derived obligations auto-pass the same way and beyond-spec additions are
SMARTS-decided and logged like any other auto-decision. A partial list never passes either way.

## Phase 2 — Red · gate: BLOCK

Write one or more failing tests per obligation. Bind each test ID to its obligation ID and move that
obligation `OPEN → MAPPED`. Run the test command from `tech-stack.md`.

- Every new test MUST fail, and fail **for the right reason** — the assertion, not an import error or a typo. A new test that passes with no implementation is wrong; fix it before continuing.
- Every pre-existing test MUST stay green. One that breaks here is a conflict — stop and surface it.

Reject the standard traps: asserting on a mock instead of behavior; a test that can never fail; a
snapshot so broad it asserts nothing; coupling to an implementation detail instead of observable
behavior; asserting on the framework's behavior rather than your own.

The reasons to skip red are known. Hearing one is the tell that this gate is about to be waived —
never the license to waive it:

| excuse | reality |
|---|---|
| "Too simple to fail first." | Simple changes have the cheapest red tests — and "too simple to test" and "too simple to break" have never been the same claim. |
| "I'll write the test right after." | A test written after green has never been seen red: it is authored against the implementation it was meant to constrain, and its power to catch the bug is never demonstrated. |
| "The test would just restate the implementation." | Then it is aimed at the wrong seam — assert the observable behavior, not the wiring. A change with no observable behavior to assert is a design finding, not an exemption. |
| "The existing suite already covers this." | Then the failing test is impossible to write — try it. If it genuinely cannot go red, the obligation is already COVERED and Phase 4 records exactly that; if it goes red, the claim was wrong and you are holding the proof. |

Gate: the runner confirms new tests red (for the right reason) and existing tests green, with every
obligation `MAPPED` to a failing test. No implementation code is written until this gate clears.

## Phase 3 — Green · gate: BLOCK

Write the **minimum** implementation that satisfies the Phase 2 tests — no speculative logic, no
gold-plating — to the conventions in `coding-standards.md`. Run the full suite. A broken pre-existing
test is a regression: fix it.

Gate: full suite green, reached by satisfying the Phase 2 tests — not by weakening them. A test's
assertions MUST be unchanged between red and green; only fixtures and setup may move. A relaxed
assertion is a gate violation.

## Phase 4 — Obligation verify · gate: BLOCK

Walk the Phase 1 list item by item. Each `MAPPED` obligation moves to `COVERED` (a real passing test
that exercises the claim) or `MISSING` (no test truly covers it). For security-relevant or
contract-critical logic, dispatch the `coverage-auditor` agent
(`{{PLUGIN_ROOT}}/agents/coverage-auditor.md`) to confirm the tests exercise the claim.

A `MISSING` obligation returns the workflow to Phase 2 — author a correct failing test, then re-run
Phase 3 — and loops until it is `COVERED`.

**Stakes:** when you block on a `MISSING` obligation, state what the untested seam leaves exposed, not
just that it is `MISSING` — one line naming the consequence: "this error path is untested; a 500 here
would reach users silently." The block is the rule; the stakes are why it is worth the friction.

Gate: every obligation `COVERED`, each backed by a passing test. Any `MISSING` blocks Phase 5.

## Phase 5 — Coverage · gate: BLOCK

Coverage scales with the maturity value (`stage:` in `CONTEXT.md`) — a rigor knob, not a promotion
gate. The threshold table is the shared `{{PLUGIN_ROOT}}/includes/maturity-coverage.md` (the
single source of truth, also used by `refactor` Phase 2).

Run the coverage command from `tech-stack.md`. **Lines and branches must both clear the threshold**
— a report satisfying one and not the other does not pass (issue #507). Below it on either → add
tests until both are met.

**Name the host you measured on**, and for a tree `tech-stack.md` marks as platform-forked, the
figure is the UNION across its supported hosts — a single-host report scores the other platform's
arm as permanently uncovered (issue #521, conditions in `{{PLUGIN_ROOT}}/includes/maturity-coverage.md`).
Where only one host is available, say so and name what is missing rather than quoting it as the
whole.

Where the surface has no coverage tooling at all, take the no-tooling exemption in
`{{PLUGIN_ROOT}}/includes/maturity-coverage.md` — which requires QUOTING the `tech-stack.md`
Coverage section that omits a command for this surface — and pass the phase on the Phase 4
obligation verify alone. Without that citation the phase STOPs: "I could not find the command" and
"this surface has none" look identical from here and demand opposite responses. Do NOT invent a
command, and do NOT silently skip the phase as though it had been run — a gate that cannot execute
still reads as satisfied, which is worse than an absent one.

**Stakes:** when coverage blocks below threshold, name the class of code left dark — the paths a later
regression could rot unnoticed — not just "below threshold." The number is the rule; the untested paths
are why it matters.

Gate: threshold met on BOTH lines and branches for the current maturity value, or the no-tooling
exemption taken WITH its citation. A test added only to move the percentage fails this gate in
spirit — it converts an honest red into a green that asserts nothing.

## Phase 6 — Lint · gate: BLOCK

Run lint, and the type-check if the project is statically typed, from `tech-stack.md`. Resolve every
error.

Gate: clean lint and type-check, zero errors — this is what clears the path to `commit-gate`.
"Mostly passes" is not passing.

## Hard rules

- MUST NOT skip, suppress, or comment out a test to clear any gate.
- MUST NOT mark an obligation `COVERED` without a passing test that exercises the claim.
- MUST NOT lower a coverage threshold without a decision recorded in `CONTEXT.md`.
- MUST NOT inline-suppress a lint rule without a written reason, and never to bypass a security-relevant rule.
- MUST NOT guess the test, coverage, or lint command — read `tech-stack.md` or STOP.
- MUST, at exit, run the follow-up harvest (`{{PLUGIN_ROOT}}/includes/harvest.md`) over any `[NEEDS-TRIAGE]` raised this run — batch-confirm promoting work to `open-tasks.md` and decisions to `open-questions.md` so nothing languishes; nothing auto-promotes interactively.