Tdd

Test-Driven Development

Implement a feature or bug fix test-first: for each behavior, write a failing test (Red), write the minimum code to pass it (Green), then clean up while tests stay green (Refactor). This skill builds new behavior — for restructuring without behavior change, use /optimus:refactor.

The Iron Law: no production code without a failing test first. If implementation code is written before its test, delete it entirely and begin the cycle fresh — do not keep it as reference, do not adapt it; write the implementation from scratch once the failing test exists.

Coming from plan mode? TDD runs in normal mode in a fresh conversation; plan-mode iterations that feed it are review-only — see $CLAUDE_PLUGIN_ROOT/skills/brainstorm/references/plan-mode-handoff.md.

Step 1: Pre-flight

If the current directory has no .git/ directory, read $CLAUDE_PLUGIN_ROOT/skills/init/references/multi-repo-detection.md and apply it; if a multi-repo workspace is detected, work inside the repo the user is targeting — ask which one if ambiguous.

If .claude/CLAUDE.md or .claude/docs/coding-guidelines.md is missing, recommend /optimus:init first; on the user's choice, continue with general best practices. Load:

• .claude/CLAUDE.md — project overview, tech stack, test runner command
• .claude/docs/coding-guidelines.md — applied during Refactor
• testing.md — test conventions: framework, file location, naming, mocking patterns. In a monorepo, load the target subproject's own docs/testing.md / docs/ files; shared guidelines come from root .claude/docs/
• docs/product/tech-stack.md and docs/product/mvp-prd.md, only if present — low-priority steering that informs decomposition and Refactor but never overrides the task source (precedence: $CLAUDE_PLUGIN_ROOT/references/sdd-mapping.md)

Verify test infrastructure

Locate the test runner command (from testing.md, CLAUDE.md, or project manifests) and run it once:

• Tests pass — proceed
• Tests fail — stop and report; a failing baseline makes Red/Green indistinguishable
• No runner found — stop and recommend /optimus:init to set up test infrastructure (its Scaffold option covers projects with no code yet)

Then find a coverage command — first match wins: the coverage section of testing.md, a runner flag (vitest --coverage, pytest --cov=., go test -cover, dotnet test --collect:"XPlat Code Coverage"), or a package.json coverage script. If found, run it once and record the Before percentage; Step 8 runs only the After measurement.

Step 2: Task and Suitability

Resolve the task with the cascade in $CLAUDE_PLUGIN_ROOT/skills/tdd/references/spec-context-detection.md. If nothing resolves and no inline argument was given, use AskUserQuestion — header "TDD scope", question "What feature or bug fix do you want to implement with TDD?", options New feature / Bug fix. Whatever the source, apply the reference's Distillation step to the final description. Resolved context feeds this step — it does not bypass Step 3 decomposition (except the scenario-driven shortcut).

Classify the task:

• Suitable — new features with testable behavior, bug fixes reproducible with a test, capabilities added to existing modules, large multi-component features (they just need careful decomposition). Proceed silently.
• Not suitable — stop and report the task, the reason, and the recommended alternative: refactoring → /optimus:refactor; documentation-only, pure styling, configuration changes, code deletion, or generated code → no testable behavior to build.
• Ambiguous — use AskUserQuestion — header "TDD fit", stating the specific concern, options Proceed with TDD / Use [alternative].

Step 3: Branch, Worktree, Decompose

Feature branch

All work happens on a new branch; the user's original branch is never modified.

1. Record the current branch (git rev-parse --abbrev-ref HEAD) — it becomes the PR/MR target.
2. Name the branch per $CLAUDE_PLUGIN_ROOT/skills/commit/references/branch-naming.md — type feat or fix from Step 2's classification.
3. Create and switch: git checkout -b <branch-name>. Report the new branch and its origin branch.

Worktree isolation (optional)

Run git worktree list; if the current directory is inside a linked worktree, skip this offer — the environment is already isolated. Otherwise use AskUserQuestion — header "Workspace", question "Use a git worktree for isolated development? Your main workspace stays on the original branch.", options Use worktree (Recommended) / Stay on branch. On yes, follow the Setup section of $CLAUDE_PLUGIN_ROOT/skills/worktree/references/worktree-setup.md with <branch-name> and <original-branch>; if creation fails, fall back to the branch workflow and say so. All subsequent commands run inside the worktree.

Decompose into behaviors

Each behavior must be observable (phrase as "When [input/action], then [outcome]"), independent (testable without the others being done), and small (one test, one assertion focus).

Scenario-driven shortcut: if the build spec contains a ## Scenarios section with ### Scenario: headings in Given/When/Then form, use those scenarios directly as the behavior list, in order — one cycle per scenario. They are stakeholder-approved acceptance criteria; do not re-derive a parallel list. Split a scenario only when a compound Then implies multiple sub-behaviors. For scenario-driven bug fixes, verify Scenario 1 reproduces the bug; prepend one if missing.

Otherwise decompose by task type: API endpoints — one behavior per response scenario; business logic — one per rule or edge case; bug fixes — the first behavior is always "reproduce the bug"; data transformations — one per step or boundary.

If more than 10 behaviors result, split into milestones of ~5-8 that each deliver a coherent slice; present the first as the current scope and list the rest as future milestones (the boundary prompt is in Step 7).

Present the numbered behavior list, then use AskUserQuestion — header "Behaviors", question "Does this decomposition look right?", options Start cycling / Adjust.

Anti-pattern — horizontal slicing. Never write all tests first, then all implementations: bulk-written tests check imagined shape, not behavior, and go insensitive to real changes. Work vertically — each cycle responds to what the previous one taught.

WRONG (horizontal):  RED: test1..test5   then   GREEN: impl1..impl5
RIGHT (vertical):    test1→impl1, test2→impl2, test3→impl3, ...

Step 4: Red — Write a Failing Test

Write one minimal test for the current behavior: follow testing.md conventions, test exactly one behavior, and name it as a behavior specification (e.g., "returns 401 when token is expired"). Before writing mocks, read $CLAUDE_PLUGIN_ROOT/skills/tdd/references/testing-anti-patterns.md — prefer real code over mocks, never assert on mock behavior.

Test-result honesty (every test run in Steps 4-8): run the command fresh, read the complete output, and state the actual result (e.g., "14 passed, 1 failed") — never "should pass". Red and Green both turn on a real observed result, so a guessed one silently breaks the discipline.

Run the test suite. The new test must fail on its assertion for the right reason, and all other tests must still pass.

• Fails for the wrong reason (import error, syntax error, infrastructure) — fix the test, not the source.
• Exception — the symbol under test doesn't exist yet: for the first behavior of a new module, class, or function, create a minimal stub (empty function, class, or module) so the run fails on the assertion instead. The stub is scaffolding, not an Iron Law violation — the failing test already exists.
• Passes unexpectedly — the behavior may already exist. Use AskUserQuestion — header "Test passed", options Skip this behavior / Strengthen the test / Investigate.

Step 5: Green — Minimal Implementation

Write the minimum code to make the failing test pass: no untested edge cases, no premature abstraction, no "while I'm here" improvements. A hardcoded return that passes is valid — later tests force generalization.

Run the test suite — all tests must pass.

• New test still fails — fix the implementation, not the test. Circuit breaker: after 3 failed attempts, stop and use AskUserQuestion — header "Implementation stuck", question "The test has failed after 3 fix attempts — this usually signals a design problem, not a code problem.":
  • Rethink the approach — reconsider the behavior's design or decomposition
  • Simplify the behavior — break it into smaller sub-behaviors
  • Skip for now — revert this cycle's implementation (git checkout -- <implementation files>; also delete implementation files the cycle newly created — git checkout does not remove untracked files), mark the test skipped per the project's convention, move to the next behavior
• Other tests broke — fix the regression before proceeding.

Bug-fix regression gate

Only when the current behavior is a bug reproduction (skip for feature behaviors). This proves the test catches the bug and the fix resolves it:

1. Commit the test separately: git add <test-file> && git commit -m "test: reproduce <bug-description>"
2. Revert only the fix: git stash push -u -- <implementation-files> (-u stashes newly created, still-untracked files). Confirm via git status/git diff that the implementation changes are actually gone.
3. Run the test — it must fail.
4. Restore the fix: git stash pop
5. Run the test — it must pass.

If the test passes at step 3 with the fix reverted, it isn't catching the bug: restore the fix (git stash pop), then rewrite the test to target the actual failure condition.

Lint / type-check

If a lint or type-check command is configured (CLAUDE.md or project manifest), run it — type errors can hide behind passing tests. Fix failures before proceeding.

Step 6: Refactor — Clean Up While Green

Review this cycle's test and implementation against coding-guidelines.md. Scope: code written in this session plus the files it directly imports, calls, or inherits from — extract duplication with those files, align naming, adjust an existing method to cleanly serve old and new usage. Do not restructure beyond that scope, add features, or handle untested edge cases. Also check the test: behavior-spec name, focused assertions, testing.md conventions.

Run the test suite when the cycle's cleanup is done; if it goes red, undo the change that broke it. Re-run the Step 5 lint / type-check as well — it last ran before this cleanup edited the code, and Step 7 commits without checking again.

Step 7: Commit and Loop

Auto-commit each completed cycle:

1. Stage the cycle's files specifically (git add <files>; git add -A only when many files changed). Never stage files that look like secrets (.env, credentials, keys) — warn the user if any appear in git status.
2. Commit with a conventional message per $CLAUDE_PLUGIN_ROOT/skills/commit/references/conventional-commit-format.md.

Then keep cycling — return to Step 4 for the next behavior without asking. Two things interrupt the loop:

• Milestone boundary — the completed behavior ends the current milestone and more remain: AskUserQuestion — header "Milestone complete", options Next milestone (present its behaviors for approval as in Step 3, then return to Step 4) / Stop here.
• The decomposition turns out to be wrong — a behavior that was really several, or one the implementation showed was misframed. Say what changed and confirm the revised list before continuing. (Step 5's circuit breaker covers the narrower case of a test that will not pass.)

Report at those boundaries rather than per cycle: which behaviors landed, their test names, and the commit hashes. If no behaviors remain, or the user stops, proceed to Step 8.

Step 8: Summary, Push, and PR/MR

Commit remaining work

If uncommitted changes exist (e.g., stopped mid-cycle), run the test suite first: mark a failing mid-cycle test skipped and note it in the summary — or surface the failure to the user before committing if skipping isn't appropriate. Stage and commit with a conventional message.

Present summary

## TDD Summary

### Behaviors Implemented
| # | Behavior | Test | Status |
|---|----------|------|--------|
| 1 | [description] | [test file]:[test name] | ✓ Complete |
| 2 | [description] | — | Not started |

### Stats
- Cycles completed: [N] of [total]
- Tests passing: [actual last-run result — e.g., "14 passed, 1 skipped"]
- Files created / modified: [lists]

### Coverage
[Run the After measurement with the Step 1 coverage command. Include this section only when both
Before and After produced a real percentage — never a half-filled block. Omit it entirely when no
coverage command was found or either run produced no parseable number.]
- Before: [X]%
- After: [Y]%
- Delta: +[Z]%

Push

Push the branch: git push -u origin <branch-name>. If the push fails, report the error and stop — skip the rest of Step 8 and leave any worktree in place; the user must push manually, then run /optimus:pr (a new /optimus:tdd invocation starts fresh — it does not resume this one). On success, report the branch, its origin branch, and the commit count.

If behaviors remain unfinished, note them and suggest a follow-up /optimus:tdd run with them as the task, started from this feature branch — each run is a fresh decomposition; there is no resume.

Next step

Recommend /optimus:code-review first: cross-cycle issues — duplication between behaviors, naming drift, coverage gaps that only surface once the whole feature shape exists — are invisible from inside a single cycle, and it reviews the branch diff with the full agent fan-out. Then /optimus:pr to create the PR/MR, which reads the ## TDD Summary block above for implementation context. Run both in this same conversation; TDD never runs gh/glab itself.

Worktree cleanup

Run this last — after the /optimus:pr recommendation, never before it. Removing the worktree deletes the directory this conversation is working in, so /optimus:pr must be able to run first.

If a worktree was used, offer cleanup rather than performing it: the user may want to keep the worktree for /optimus:pr or follow-up work. If they accept, follow the Cleanup section of $CLAUDE_PLUGIN_ROOT/skills/worktree/references/worktree-setup.md; if they decline, follow that section's keep-the-worktree note.