msd-core/gsd-core/references/execute-mvp-tdd.md

Execute-Phase — TDD Gate (Runtime Enforcement)

Loaded by execute-phase workflow and gsd-executor agent when TDD_MODE=true for the phase (#4011 — the gate no longer requires MVP mode; MVP may imply TDD, but TDD never requires MVP). Defines the runtime gate that blocks behavior-adding tasks until a failing-test commit exists.

When this gate fires

• TDD_MODE is true (resolved from --tdd flag → workflow.tdd_mode config). MVP mode is NOT required (#4011).
• The current task being executed has tdd="true" in its <task> frontmatter (set by the planner per Phase 1).
• The task's <behavior> block lists at least one expected behavior.

If any of these is false, the gate is inactive — execution proceeds normally.

What the gate checks

For each task gated by TDD, the executor MUST verify (before running the implementation step):

1. A failing-test commit exists. Search git log on the current branch for a commit matching test({phase}-{plan}) whose subject mentions the same plan as the current task. The commit must touch a test file (*.test.*, *.spec.*, tests/**).
2. The test was actually red — INTENTIONALLY (#3770). A nonzero exit is not RED by itself: syntax errors, zero-test discovery, fixture crashes, parser errors, and unrelated assertions are INVALID_RED. The executor must persist the RED evidence record (command, exit code, failing test, expected result from <behavior>, actual result) and verify it:

   gsd_run check tdd-red-evidence <record.json> --raw
   

   • RED_EVIDENCE_OK (reason target_test_failed): the TARGET test named by the plan failed on a real assertion — the ONLY verdict that authorizes GREEN.
   • INVALID_RED (reasons unexpected_green, zero_tests_discovered, nonzero_exit_without_test_failure, fixture_or_load_failure, no_target_test_failure, invalid_record, unreadable_record): the gate trips — halt, fix the RED phase (test identity, fixture, discovery), and re-verify before any implementation step. A RED: prefix or (RED) tag in the commit message is NOT sufficient evidence on its own.
3. No implementation commit yet. No feat({phase}-{plan}) commit may exist for the same plan ID before the failing-test commit.

If any check fails, the gate trips. For check 2, an INVALID_RED verdict (check tdd-red-evidence) trips the gate — the executor MUST halt and block the implementation step.

What "behavior-adding task" means

A task is behavior-adding when:

• Its frontmatter has tdd="true" AND
• Its <behavior> block names at least one user-visible outcome (not a config-only or doc-only task) AND
• Its <files> list includes at least one source file (not exclusively docs/tests/config files such as *.md, *.json, *.test.*, *.spec.*, *.yml, *.yaml, *.toml, *.ini, .env*)

Pure documentation, configuration, or test-only tasks are skipped by this gate even when both modes are active.

What happens when the gate trips

The executor MUST:

1. Halt before running the task's implementation step.

2. Emit a structured halt report:

TDD GATE TRIPPED — Plan {plan_id}, Task {task_id}

Reason: {missing_red_commit | red_commit_not_failing | feat_before_test | invalid_red}

Behavior expected to be tested:

• {first behavior bullet}

Required next step:

1. Write a failing test for the behavior above.
2. Commit it as: test({phase}-{plan}): {short description}
3. Re-run /gsd execute-phase

3. Exit the current execution wave cleanly. Do NOT roll back any prior commits in the same wave.
4. Update `STATE.md` with `last_gate_trip: {plan_id}/{task_id}` so the user can resume after writing the test.

## Escalation: end-of-phase TDD review under TDD

The existing end-of-phase TDD review (in `workflows/execute-phase.md`'s `tdd_review_checkpoint` step) is normally **advisory** — it surfaces gate violations but does not block phase completion.

Under TDD mode, escalate this to **blocking**:
- If any TDD plan is missing a RED or GREEN commit, the executor MUST refuse to mark the phase complete.
- The user is shown the same review table, but the verdict line reads:
> "Phase blocked: {N} TDD plan(s) violate the RED→GREEN gate sequence under TDD. Resolve and re-run /gsd execute-phase, or override with `/gsd execute-phase {phase} --force-mvp-gate` to ship anyway."

The `--force-mvp-gate` flag is documented but not introduced by this plan — it is the escape hatch the spec mentions; if the user later builds it, the workflow already references the contract.

## What this gate does NOT do

- It does not enforce REFACTOR commits. REFACTOR remains optional (per `gsd-core/references/tdd.md`).
- It does not check test quality (the test could be trivially weak). That's the planner's job. It DOES check that the RED failure was intentional — the target test failing an assertion (#3770).
- It does not run tests. The executor only inspects git log + file system. Running tests is the implementation step's job.
- It does not gate config-only or doc-only tasks (see "behavior-adding task" definition).

## Compatibility with existing TDD discipline

This gate is additive to `gsd-core/references/tdd.md`. Tasks not under TDD mode continue to use the existing advisory TDD discipline (RED/GREEN/REFACTOR commits with end-of-phase review checkpoint). Only the runtime gate and the blocking escalation are new.