agentmods.dev

tdd

A guide to Test-Driven Development (TDD), a method where you write a failing test, make it pass with minimal code, then clean up the code.

In plain words
What is it for?
Use it when writing tests first, following the red-green-refactor cycle, designing test data, or reviewing and improving test suites.
Why use it?
It gives coding agents a repeatable way to design tests and implement changes without losing the intended behavior.

Skill for Claude CodeCodex

3 12d ago A scan 96 tokens copy · 98% MIT
View the source file PyModel/react-frontend-skills
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/pymodel/react-frontend-skills/tdd
Any agent
npx skills add PyModel/react-frontend-skills --skill tdd
Clone the repo
git clone --depth 1 https://github.com/PyModel/react-frontend-skills

Made for: Claude Code, Codex.

Per session 96 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,341 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin 98% copy Near-identical to another mod 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 $0.00096 $0.01341
Opus 5 $0.00048 $0.00671
Sonnet 5 $0.00019 $0.00268
Haiku 4.5 $0.00010 $0.00134

Measured 2d ago against content hash 342067a0d37a, 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 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.

Origin

This is a copy

98% identical to tdd — 3 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

skills/tdd/SKILL.md · 123 lines

How it starts

The opening of the file, as written. The whole thing — 123 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Community Test-Driven Development Best Practices

Comprehensive guide to Test-Driven Development practices, designed for AI agents and LLMs. Contains 42 rules across 8 categories, prioritized by impact to guide test writing, refactoring, and code generation.

When to Apply

Reference these guidelines when:

  • Writing new tests using TDD workflow
  • Implementing the red-green-refactor cycle
  • Designing test structure and organization
  • Creating test data and fixtures
  • Reviewing or refactoring existing test suites

TDD Workflow

  1. RED: Write a failing test that defines desired behavior
  2. GREEN: Write minimal code to make the test pass
  3. REFACTOR: Clean up code while keeping tests green
  4. Repeat for each new behavior

Rule Categories by Priority

Priority Category Impact Prefix
1 Red-Green-Refactor Cycle CRITICAL cycle-
2 Test Design Principles CRITICAL design-
3 Test Isolation & Dependencies HIGH isolate-
4 Test Data Management HIGH data-
5 Assertions & Verification MEDIUM assert-
6 Test Organization & Structure MEDIUM org-
7 Test Performance & Reliability MEDIUM perf-
8 Test Pyramid & Strategy LOW strat-

Quick Reference

1. Red-Green-Refactor Cycle (CRITICAL)

  • cycle-write-test-first - Write the Test Before the Implementation
  • cycle-minimal-code-to-pass - Write Only Enough Code to Pass the Test
  • cycle-refactor-after-green - Refactor Immediately After Green
  • cycle-verify-test-fails-first - Verify the Test Fails Before Writing Code
  • cycle-small-increments - Take Small Incremental Steps
  • cycle-maintain-test-list - Maintain a Test List

2. Test Design Principles (CRITICAL)

  • design-test-behavior-not-implementation - Test Behavior Not Implementation
  • design-one-assertion-per-test - One Logical Assertion Per Test
  • design-descriptive-test-names - Use Descriptive Test Names
  • design-aaa-pattern - Follow the Arrange-Act-Assert Pattern
  • design-test-edge-cases - Test Edge Cases and Boundaries
  • design-avoid-logic-in-tests - Avoid Logic in Tests

Read the full file on GitHub · 123 lines

Files

What ships with it

45 files 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 · 123 lines · 96 tokens per session scan A 342067a0d37a

Subscribe to this mod's changes

tdd is a skill published in the GitHub repository PyModel/react-frontend-skills (3 stars, last pushed 12d ago), licensed MIT. It adds 96 tokens to every session and 1,341 once invoked, about $0.0005 per session on Opus 5. A static security scan graded it A with 0 findings. It is 98% identical to tdd, differing in 3 lines, and is treated as a copy.

FrontendTestingWriting and docsagent-skillsai-agentsai-coding-assistantclaude-codecodexcursor
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