tdd

A Test-Driven Development guide for high-risk code. TDD means writing a failing test first, then the smallest code that passes it, and finally improving the code safely.

In plain words
What is it for?
Use it to define expected behavior before implementation, cover successful and failure cases, and refactor with tests protecting the behavior.
Why use it?
It reduces the chance that silent errors remain in authentication, permissions, billing, core rules, data handling, or irreversible operations.

Skill for Claude CodeCodex

Install

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.

agentmods
npx agentmods add skills/oreum-ai/smartstack/tdd
Any agent
npx skills add oreum-ai/smartstack --skill tdd
Clone the repo
git clone --depth 1 https://github.com/oreum-ai/smartstack

Made for: Claude Code, Codex.

Per session 0 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 375 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5 $0.00000 $0.00375
Opus 5 $0.00000 $0.00187
Sonnet 5 $0.00000 $0.00075
Haiku 4.5 $0.00000 $0.00038

Measured yesterday against content hash 90f5b9cfdc5a, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

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 yesterday.

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.

ai-rules/skills/tdd/SKILL.md · 31 lines

What it actually says

Skill: TDD (Test-Driven Development)

When to use

Before writing any high-risk logic: authentication, authorization, money/billing, core domain rules, data integrity, anything irreversible. Required there because a silent bug is dangerous or expensive.

The cycle: Red → Green → Refactor

  1. Red — write a failing test first. State the expected behavior as a test before the code exists. Name it like a sentence. Run it; watch it fail. A test that passes before you write the code tests nothing.
  2. Green — write the minimum code to pass. Don't gold-plate; just make it green.
  3. Refactor — clean it up with the test as a safety net. Improve names/structure; the test proves you didn't change behavior.
  4. Repeat for the next behavior / the next failure path.

What to cover before moving on

  • The happy path (valid input → expected result).
  • Every failure path (invalid input, missing data, unauthorized, boundary values).

Rules

  • One behavior per test; deterministic; independent (no shared mutable state, no order dependence).
  • Test the contract (inputs → outputs/side-effects), not internal implementation.
  • For data logic, use fakes/mocks or a disposable test database — never prod data.
  • A red test blocks the ship. Never comment out a failing test to "make it pass."

Procedure with your AI assistant

  1. Read rules/testing.md and the relevant context/ file.
  2. Write the failing test(s) for the next behavior; confirm they fail for the right reason.
  3. Implement the minimum code; run until green.
  4. Refactor; keep green.
  5. Record any bug found along the way in the error ledger.
Changes

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.

  1. yesterday First seen · 31 lines · 0 tokens per session scan A 90f5b9cfdc5a

Subscribe to this mod's changes

tdd is a skill published in the GitHub repository oreum-ai/smartstack (5 stars, last pushed 3mo ago), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 375 tokens. 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 2026-08-31.

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