# Tdd > Apply Test-Driven Development workflow for new features and bugfixes. Use when this capability is needed. - Skill: `tomevault-io/tdd-21` (Agent Skill, multi-file: 2 files) - Install (CLI): `npx skillmds@latest add tomevault-io/tdd-21` - Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/tdd-21/raw - Safety review: pending (external: skill-scanner PASS, skillspector PASS) - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Productivity - Author: tomevault-io (https://skillmd.com/u/tomevault-io) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/tomevault-io/tdd-21 --- # TDD Protocol ## Core Principle - **TDD First**: Test-Driven Development is the default approach. - **Goal**: Prioritize behavioral correctness and regression safety over formal compliance. ## Workflow 1. **Requirement Synthesis**: Briefly summarize the requirements before coding. 2. **Test Specification**: Write tests describing the expected behavior (unit, integration, or E2E). 3. **Implementation**: Update the logic only to the extent required to satisfy those tests. ## Mandatory Rules - **No Test, No Code**: Every new feature or bugfix must include relevant test coverage. - **Black-Box Testing**: Validate observable behavior, not internal implementation details. - **Merge Requirement**: Tests are mandatory for completion unless an explicit exception is documented. ## Preferred Practice - **Red-Green-Refactor**: Start with a failing test whenever practical. - **Right-Sized Testing**: - **Unit Tests**: For pure logic and isolated functions. - **Integration Tests**: For system interactions and API boundaries. - **E2E Tests**: For critical user journeys and "happy paths." ## Explicit Exceptions (Must be justified) - Pure refactoring (where behavior remains identical). - Exploratory spikes or R&D. - UI/Styling iterations where unit tests offer diminishing returns. - Complex integrations where mocking is counterproductive. - Emergency hotfixes (requires a follow-up ticket for test debt). ## Quality Bar - **Readability**: Tests must serve as documentation for the feature. - **Reliability**: Tests must be deterministic (no flakes) and decoupled from implementation internals. --- > Converted and distributed by [TomeVault](https://tomevault.io/claim/smartfrog) — claim your Tome and manage your conversions.