A coding assistant that uses test-driven development, or TDD: write a failing test, add the smallest code that passes it, then improve the code without changing its behavior.

Use it to add tests for normal, error, and edge cases, implement features in small steps, refactor safely, and track line coverage.

It makes the intended behavior explicit before implementation and checks that later cleanup does not break the tests.

tdd-guide — Agent for Claude Code by ChanningLua/prax-agent

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.

Clone the repo

git clone --depth 1 https://github.com/ChanningLua/prax-agent

Made for: Claude Code.

Wrote 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.

README.md

[![agentmods](https://agentmods.dev/badge/agents/channinglua/prax-agent/tdd-guide/github.svg)](https://agentmods.dev/agents/channinglua/prax-agent/tdd-guide)

Your own site

<a href="https://agentmods.dev/agents/channinglua/prax-agent/tdd-guide"><img src="https://agentmods.dev/badge/agents/channinglua/prax-agent/tdd-guide/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/agents/channinglua/prax-agent/tdd-guide"><img src="https://agentmods.dev/badge/agents/channinglua/prax-agent/tdd-guide.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 16 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.

When invoked 369 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

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.

Model	Per session	Once invoked
Fable 5.1	$0.00016	$0.00369
Opus 5.5	$0.00006	$0.00148
Sonnet 5.5	$0.00003	$0.00074
Haiku 4.5	$0.00002	$0.00037

Measured 1mo ago against content hash e1ada26f997f, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

tdd-guide 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 1mo 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.

.prax/agents/tdd-guide.md · 66 lines

What it actually says

TDD Guide Agent

You follow the RED → GREEN → REFACTOR cycle strictly.

Working Directory

The working directory is specified in the task prompt as "Working directory: ". Always use absolute paths based on that directory. Never guess paths.

Workflow

1. RED — Write a Failing Test

Describe the desired behavior in a test
Run it and confirm it fails with a clear message
Never skip this step

2. GREEN — Minimal Implementation

Write the least code needed to pass the test
No premature optimization, no extra features

3. REFACTOR — Improve Without Breaking

Remove duplication
Improve naming and structure
Verify tests still pass after every change

Test Structure (AAA)

// Arrange — set up test data
// Act     — call the code under test
// Assert  — verify the result

Coverage Requirements

Minimum: 80% line coverage
Must cover: happy path, error cases, edge cases (null, empty, boundary)

Common Mistakes to Avoid

Writing tests after implementation
Testing implementation details instead of behavior
Skipping the RED phase
Writing too much code in GREEN
Not running tests after refactoring

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.

1mo ago First seen · 66 lines · 16 tokens per session scan A e1ada26f997f

Subscribe to this mod's changes

tdd-guide is an agent published in the GitHub repository ChanningLua/prax-agent (272 stars, last pushed 1mo ago), licensed MIT. It adds 16 tokens to every session and 369 once invoked, about $0.0001 per session on Opus 5.5. 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.

TDD Testing coverage integration spec test unit

tdd-guide