Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add skills/codagent-ai/agent-skills/implement-with-tddnpx skills add Codagent-AI/agent-skills --skill implement-with-tddgit clone --depth 1 https://github.com/Codagent-AI/agent-skillsWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/codagent-ai/agent-skills/implement-with-tdd)<a href="https://agentmods.dev/skills/codagent-ai/agent-skills/implement-with-tdd"><img src="https://agentmods.dev/badge/skills/codagent-ai/agent-skills/implement-with-tdd.svg" alt="Measured on agentmods" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00046 | $0.02290 |
| Opus 5 | $0.00023 | $0.01145 |
| Sonnet 5 | $0.00009 | $0.00458 |
| Haiku 4.5 | $0.00005 | $0.00229 |
Grade A, and why
implement-with-tdd scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 5d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 320 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Test-Driven Development (TDD)
Overview
Write the test first. Watch it fail. Write minimal code to pass.
Core principle: Watch the test fail. Only then is it proven to test the right thing.
Violating the letter of the rules is violating the spirit of the rules.
When to Use
Always:
- New features
- Bug fixes
- Refactoring
- Behavior changes
Exceptions (skip TDD only for these; otherwise follow the full TDD cycle):
- Throwaway spikes that will never be merged (branch must be deleted before implementation begins; any code carried forward requires full TDD)
- Generated code (scaffolded, not behavior-bearing)
- Configuration-only changes
Thinking "skip TDD just this once"? Stop. That's rationalization.
The Iron Law
NO PRODUCTION CODE WITHOUT A FAILING TEST FIRST
Write code before the test? Delete it. Start over.
No exceptions:
- Don't keep it as "reference"
- Don't "adapt" it while writing tests
- Don't look at it
- Delete means delete
Implement fresh from tests. Period.
Choosing Test Type
Honor any integration or E2E coverage explicitly required by the task's supplied requirements or test plan. For behavior without a higher-layer requirement, prove it at the lowest layer that can adequately detect the relevant failure:
- Unit — pure logic, validation, transformations, calculations. No I/O, no wiring. Fast (<100ms).
- Integration — components wired together: database queries, middleware chains, API clients, config reaching runtime. If the bug would only manifest when components connect, it needs an integration test.
- E2E — critical user flows only (login, checkout, onboarding). Expensive, slow, flaky-prone. Don't use for logic that can be tested at a lower level.
Do not substitute a unit test for required integration or E2E coverage, and do not duplicate the same assertion at multiple layers without a distinct risk. When implementation tasks are supplied, keep each automated obligation in the same task as the behavior it protects.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 5d ago First seen · 320 lines · 46 tokens per session scan A e500c686033a
implement-with-tdd is a skill published in the GitHub repository Codagent-AI/agent-skills (30 stars, last pushed 1mo ago), licensed MIT. It adds 46 tokens to every session and 2,290 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
Other skills, from other repositories
engram-testing-coverage
TDD and coverage standards for Engram. Trigger: When implementing behavior changes in any package.
tdd
Test-driven development. Use when the user wants to build features or fix bugs test-first, mentions "red-green-refactor", or wants integration tests.
strict-tdd
Strict RED->GREEN->REFACTOR test-driven development with enforcement. Never write production code before a failing test. Atomic commits per TDD cycle.
tdd
This skill should be used when the user wants to implement features or fix bugs using test-driven development. Enforces the RED-GREEN-REFACTOR cycle with vertical slicing, context isolation between test writing and implementation, human checkpoints, and auto-test feedback loops. Uses multi-agent orchestration with the…
conductor-implement
Execute tasks from a track's implementation plan following TDD workflow.
mobiai-mobile-tdd
You MUST use this before writing any implementation code for a mobile feature, bug fix, refactor, or behavior change. Tests come before implementation — no exceptions.