Openspec Plus TDD

OpenSpec Plus TDD

Mission

Strict RED-GREEN-REFACTOR per test for OpenSpec change implementation. Every test — whether derived from a Gherkin scenario relevant to the slice in spec.md, written for a unit, edge case, helper, or error path — goes through its own atomic cycle before the next test begins. Production code exists only to make a previously-failing test pass. Surgical changes, simplicity first, no speculative abstractions, every changed line traces to a slice task.

Gherkin scenarios in spec.md are the canonical source for acceptance tests: every scenario relevant to the slice MUST become at least one test. The implementer is encouraged to add additional tests — unit tests for individual functions, edge-case tests, helper tests, error-path tests — when fast-feedback granularity is valuable. Every test follows the same cycle.

Loaded by openspec-plus-apply (subagent prompt + inline mode) before any code is written.

RIGID. NEVER write production code before a test fails for the right reason. NEVER write tests for multiple cases before the first one is GREEN. NEVER skip the REFACTOR assessment. NEVER mark a task [x] while a relevant test is failing or skipped. NEVER add comments for non-complex logic. NEVER refactor code outside the slice. NEVER write any code (test or production) before reading the project's referenced coding/testing standards. NEVER ship without covering every Gherkin scenario in spec.md with at least one test. Letter and spirit are the same.

Red flags — STOP, you are about to violate this skill:

• "I'll write the test after, it's faster"
• "Too simple to need a test"
• "Manually verified, that's enough"
• "Gherkin scenario is vague, generic test is fine"
• "Skip this failing test, circle back later"
• "Mark .skip to unblock the slice"
• "While I'm here, clean up the adjacent code"
• "Add an interface in case we swap implementations"
• "Short comment explains the obvious"
• "Error handling for cases that can't happen"
• "Test passed first run, must be right"
• "Let me write tests for all the cases first, then implement"
• "Test 1 done — I have a clear picture, let me write all the rest at once"
• "I have a clear picture of all 5 cases — let me write them all"
• "Writing one test at a time is slower"
• "These cases are related, I'll batch them"
• "The code I'm about to write covers test 2 anyway, no need to write its test separately first"
• "Acceptance tests cover the happy path — skip the unit/edge tests"
• "Scenarios covered, no need to add granular tests even though the helper has edge cases"
• "Nothing to refactor, skip the assessment"
• "I know the project conventions, no need to re-read AGENTS.md"
• "AGENTS.md has many rules — I'll apply the ones that feel relevant"

None justify production code without a red test, ignored failures, speculative abstractions, comments on obvious code, or scope expansion.

The Iron Law

NO PRODUCTION CODE WITHOUT A FAILING TEST

Every test — acceptance, unit, edge case, helper, error path — must be observed to fail for the right reason before the production code that makes it pass is written. Test not observed to fail = test proves nothing. Code written first = delete it, start over. No exceptions without explicit user permission.

Mandatory Acceptance Coverage

Every Gherkin scenario relevant to the slice in spec.md MUST become at least one test. The scenario IS the acceptance contract; the test IS the verification. A slice cannot ship with an uncovered scenario, even if all other tests pass.

Encouraged Granular Coverage

Beyond acceptance tests, add unit/edge/helper/error tests when valuable (non-trivial branches, null/empty inputs, boundary values, error paths). Same RED-GREEN-REFACTOR cycle — no special handling regardless of test origin.

Inputs

• Slice tasks (tasks.md)
• Slice spec requirements + Gherkin scenarios (spec.md)
• Slice design decisions (design.md)
• Project standards (AGENTS.md / CLAUDE.md / GEMINI.md if in context)
• Existing code in slice's affected files

NEVER read source outside the slice's affected files.

Workflow

Phase 0: Pre-RED — read project's coding/testing conventions; follow strictly

Phase 1+: Plan the test set for the slice:
  Mandatory:  one test per Gherkin scenario relevant to the slice in spec.md
  Encouraged: additional unit / edge-case / helper / error-path tests
              when fast-feedback granularity is valuable

Phase 2+: For each test, ONE AT A TIME (any test, in any order):
  Follow the Per-Test State Machine (digraph below) atomically.
  Do NOT begin the next test until the current one terminates at
  "Test Complete".

After all tests complete AND every Gherkin scenario relevant to the slice is covered, run
the slice's pre-mark gate.

Per-Test State Machine (MANDATORY)

Every test traverses this cycle end-to-end before work begins on the next. Atomic per test — no shortcuts, no batching, no skipping nodes. Applies to all test types (acceptance and granular).

Per-test cycle: START → RECORD STATE BEFORE (file path + count + names) → RED (write ONE failing test K) → VERIFY-RED (fails for expected reason? no → fix test, retry) → GREEN (minimum production code for K only) → VERIFY-GREEN (K passes, others green, output pristine? no → fix production code, retry) → REFACTOR ASSESS (needed? yes → act, verify green, revert if broken; no → record "not needed — reason") → RECORD STATE AFTER (count = previous + 1) → TEST K COMPLETE → return to START for K+1 (or end if all done AND all Gherkin scenarios covered).

The cycle forbids:

• Starting test K+1 before K reaches COMPLETE
• Skipping REFACTOR assessment — every test passes through it
• Skipping state recording — audit trail is mandatory
• Ending slice with uncovered Gherkin scenarios

Concrete Pattern: WRONG vs RIGHT

This is the single most-violated rule. Read both examples carefully.

WRONG — Batching (the model's training default)

Implementer opens empty test file.
Writes test 1, test 2, test 3, test 4, test 5 in one pass.
Runs tests — all 5 fail.
Writes production code covering all 5 cases in one pass.
Runs tests — all 5 pass.
Reports DONE.

This is NOT TDD. Each test passed immediately when production code arrived. You never observed test 1 failing in isolation. You never refactored after each green. You wrote the whole solution in your head and dumped it onto disk.

The end state (5 tests, 5 features) is identical to RIGHT — but the discipline is absent. The reviewer cannot tell from end state alone, but YOU know you batched.

RIGHT — One Test At A Time

State: 0 tests.

Test 1 (acceptance — Gherkin "valid login"):
  Write test 1 (1 test, 1 failing). RED: "expected `Email required`, got undefined" ✓
  Write minimum production. GREEN: 1 passing, pristine ✓
  Refactor: no duplication, names clear → "not needed."

Test 2 (acceptance — Gherkin "invalid password"):
  Write test 2 (2 tests, 1 failing). RED: "expected `Invalid password`, got `Internal error`" ✓
  Write minimum production. GREEN: 2 passing ✓
  Refactor: extracted `mapAuthError` helper. Tests green.

Test 3 (unit — edge case for `mapAuthError(null)`):
  Write test 3 (3 tests, 1 failing). RED: "expected `Invalid input`, got TypeError" ✓
  Add null guard. GREEN: 3 passing ✓. Refactor: not needed.

[repeat for each test...]

Tests 1-2: Gherkin scenarios (mandatory acceptance). Test 3: implementer-initiated edge case (granular). All follow the same per-test cycle.

If you find yourself thinking "I know all 5 cases, let me write them all at once" — STOP. That is the violation. Delete what you just wrote. Restart from test 1.

Why "I'll write all the tests, then implement" is wrong

• Test 2 might pass immediately when you implement test 1 — you'd never know if test 2 actually tests what you think.
• No checkpoint forces you to confront edge cases per test. Edge cases get glossed.
• You miss refactor opportunities that emerge between tests.
• The discipline is the value, not the end state.

Phase 0: Pre-RED — Read Referenced Conventions

Before ANY code (mandatory, once per slice):

1. AGENTS.md / CLAUDE.md / GEMINI.md (or equivalents at project root, .claude/, .opencode/, docs/)
2. Follow references inside those files to other docs (coding standards, testing conventions, patterns)
3. Slice's affected files — absorb local style

These files are the contract — follow every documented rule strictly, end-to-end (no cherry-picking). Re-read per slice (files may have been updated). Do NOT proceed to Phase 1 before reading is done.

Phase 1: RED — Failing Test (One At A Time)

The test you write at this phase is one of two kinds:

1. Acceptance test — translated from a Gherkin scenario.

A Gherkin scenario in spec.md:

#### Scenario: User logs in with valid credentials
GIVEN a user account exists with email `alice@example.com` and password `correct-pw`
WHEN the user submits the login form with those credentials
THEN the response sets a session cookie
AND the user is redirected to `/dashboard`

Translate directly into one minimal acceptance test:

test('logs in with valid credentials', async () => {
  await createUser({ email: 'alice@example.com', password: 'correct-pw' });

  const response = await submitLogin({ email: 'alice@example.com', password: 'correct-pw' });

  expect(response.headers['set-cookie']).toMatch(/session=/);
  expect(response.status).toBe(302);
  expect(response.headers.location).toBe('/dashboard');
});

2. Granular test — implementer-initiated for a unit, edge case, helper, or error path

Example: while implementing the login above, the implementer factors out a mapAuthError helper. They add a unit test for it:

test('mapAuthError handles null input', () => {
  expect(() => mapAuthError(null)).toThrow('Invalid input');
});

This test was not derived from a Gherkin scenario — it was added because the helper's null case needs fast-feedback coverage. It follows the same cycle.

Rules (both kinds):

• One test at a time — never batch. Test name describes behavior, not implementation.
• Real code paths; mocks ONLY when dependency unavailable. Test the OUTCOME, not call sequence.
• Acceptance: translate Gherkin faithfully. Granular: state the unit's contract explicitly.

Phase 2: VERIFY-RED — Watch It Fail Correctly

MANDATORY. NEVER SKIP.

Run the test. Confirm:

1. Test FAILS (not errors, not passes).
2. Failure message matches what scenario implies.
3. Failure is because feature is missing — not typo, not missing import, not setup bug.

Test passes immediately → feature exists or test is wrong. Fix the test. Test errors → fix error, re-run until it fails for the expected reason.

Phase 3: GREEN — Minimum Production Code

Simplest code that passes the test.

• No features beyond what the failing scenario requires
• No abstractions for single-use code
• No flexibility/configuration the scenario didn't ask for
• No error handling for impossible cases
• Match existing patterns

If 200 lines and 50 would do — rewrite.