test-driven-development

A test-first way to change software: write a failing test, make the smallest code change that passes it, then improve the code while the test stays green. TDD means test-driven development.

In plain words
What is it for?
Use it for new behavior, bug fixes, refactoring that must preserve existing behavior, and regression tests, except when tests are unsuitable for disposable or documentation-only work.
Why use it?
It checks the intended behavior before implementation and helps prevent bugs from returning, while keeping changes focused.

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/thiientv/godmode/test-driven-development
Any agent
npx skills add thiientv/godmode --skill test-driven-development
Clone the repo
git clone --depth 1 https://github.com/thiientv/godmode

Made for: Claude Code, Codex.

Per session 75 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 463 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 $0.00075 $0.00463
Opus 5 $0.00037 $0.00231
Sonnet 5 $0.00015 $0.00093
Haiku 4.5 $0.00007 $0.00046

Measured 2d ago against content hash 7113614524d5, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

test-driven-development 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 2d 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.

skills/test-driven-development/SKILL.md · 51 lines

What it actually says

Test-Driven Development

The test is an executable statement of behavior, not a coverage decoration.

Red-green-refactor

  1. Red: name one behavior and write the smallest test at the highest seam that can fail for the missing behavior.
  2. Verify red: run the focused command. Confirm it fails because the behavior is absent, not because of a typo, broken fixture, or setup error.
  3. Green: implement the simplest production change that makes the test pass. Do not add speculative options or unrelated cleanup.
  4. Verify green: run the focused test and relevant existing tests.
  5. Refactor: improve names, duplication, and boundaries while keeping the suite green. Add the next behavior only after the current loop is stable.

Honest tests

  • Assert user-visible or contract-visible behavior, not private call counts.
  • Prefer real collaborators; mock only an expensive, nondeterministic, or unavailable boundary and state why.
  • Make failures diagnostic: clear name, small fixture, one cause.
  • Include error, empty, boundary, retry, ordering, and permission cases when they are part of the contract.

Exceptions

For a prototype, generated output, or docs-only change, state why test-first is not useful and choose another observable check. “I will test later” is not an exception for production behavior.

Use test-design.md when the test seam or fixture quality is unclear. Pair with root-cause-debugging for an existing failure and completion-verification at the final gate.

Completion condition

The loop is credible when the test was observed failing for the intended reason, passes after the change, neighboring checks remain green, and the remaining untested behavior is named.

Files

What ships with it

1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

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. 2d ago First seen · 51 lines · 75 tokens per session scan A 7113614524d5

Subscribe to this mod's changes

test-driven-development is a skill published in the GitHub repository thiientv/godmode (93 stars, last pushed 6d ago), licensed MIT. It adds 75 tokens to every session and 463 once invoked, about $0.0004 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.

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