tdd

name	tdd
description	Build features and fix bugs using a strict Test-Driven Development workflow (Red-Green-Refactor), with regression-first bugfixing and explicit clarification when expected behavior is ambiguous. Use when Codex must implement or repair behavior with high confidence, test evidence, and minimal-risk changes.

TDD

Use this skill to implement features and fix bugs with a test-first workflow.

Workflow

1. Classify task and goal.

• Determine whether the request is feature, bugfix, or mixed.
• Capture expected behavior, acceptance criteria, and non-functional constraints.
• If behavior is ambiguous, ask concise clarifying questions before writing tests.

2. Resolve ambiguity before test design.

• Ask only high-impact questions that change expected behavior or test assertions.
• Ask up to 2 rounds of clarifying questions.
• If still unresolved, proceed with explicit assumptions and mark risk.

3. Write failing test first (Red).

• Add or update tests that express expected behavior before production changes.
• For bugfixes, reproduce the bug with a regression test that fails on current code.
• Prefer the smallest test scope that proves behavior.

4. Implement minimal change (Green).

• Modify production code only after the failing test exists.
• Make the minimal change needed for tests to pass.
• Avoid broad refactors during this step.

5. Refactor safely (Refactor).

• Improve design only with tests passing.
• Keep behavior unchanged while reducing complexity and duplication.

6. Strengthen test coverage.

• Add edge, negative, and boundary cases relevant to risk.
• Validate that original failing scenario is permanently covered.

7. Run verification.

• Run focused tests first, then broader suite as appropriate.
• If tests fail, return to Red and iterate.

8. Report outcome.

• Summarize failing test introduced, code change, and proof of pass state.
• List assumptions, residual risks, and follow-up tests if needed.

Mode Rules

• Never implement behavior without first expressing it in a failing test.
• For bugfixes, require a regression test that fails before the fix.
• Keep each cycle small and reversible.
• Prefer deterministic tests over brittle integration-only checks.

Output Rules

• Use tdd_output_template.md for final responses.
• Include the exact tests added/updated and what they verify.
• Explicitly separate facts from assumptions.
• If blocked by ambiguity, show the missing detail and why it affects test validity.

References

• tdd_cycle_checklist.md
• bugfix_regression_playbook.md
• test_design_heuristics.md
• tdd_output_template.md