Borrowing it
Nothing to install: this file belongs to wbern/agent-instructions. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/wbern/agent-instructions/main/.claude/skills/tdd/SKILL.mdgit clone --depth 1 https://github.com/wbern/agent-instructionsWrote 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/wbern/agent-instructions/tdd)<a href="https://agentmods.dev/skills/wbern/agent-instructions/tdd"><img src="https://agentmods.dev/badge/skills/wbern/agent-instructions/tdd/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.
<a href="https://agentmods.dev/skills/wbern/agent-instructions/tdd"><img src="https://agentmods.dev/badge/skills/wbern/agent-instructions/tdd.svg" alt="Reviewed on agentmods" width="80" 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 5.1 | $0.00013 | $0.01101 |
| Opus 5.5 | $0.00005 | $0.00440 |
| Sonnet 5.5 | $0.00003 | $0.00220 |
| Haiku 4.5 | $0.00001 | $0.00110 |
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 2mo 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 — 103 lines — stays where its author put it; the contents beside it link to each section on GitHub.
TDD Reminder
General Guidelines
Output Style
- Never explicitly mention TDD in code, comments, commits, PRs, or issues
- Write natural, descriptive code without meta-commentary about the development process
- The code should speak for itself - TDD is the process, not the product
Beads is available for task tracking. Use mcp__beads__* tools to manage issues (the user interacts via bd commands).
Plan File Restriction
NEVER create, read, or update plan.md files. Claude Code's internal planning files are disabled for this project. Use other methods to track implementation progress (e.g., comments, todo lists, or external tools).
TDD Fundamentals
The TDD Cycle
The foundation of TDD is the Red-Green-Refactor cycle:
-
Red Phase: Write ONE failing test that describes desired behavior
- The test must fail for the RIGHT reason (not syntax/import errors)
- Only one test at a time - this is critical for TDD discipline
- Exception: For browser-level tests or expensive setup (e.g., Storybook
*.stories.tsx), group multiple assertions within a single test block to avoid redundant setup - but only when adding assertions to an existing interaction flow. If new user interactions are required, still create a new test. Split files by category if they exceed ~1000 lines.
- Exception: For browser-level tests or expensive setup (e.g., Storybook
- Adding a single test to a test file is ALWAYS allowed - no prior test output needed
- Starting TDD for a new feature is always valid, even if test output shows unrelated work
- For DOM-based tests, use
data-testidattributes to select elements rather than CSS classes, tag names, or text content - Avoid hard-coded timeouts both in form of sleep() or timeout: 5000 etc; use proper async patterns (
waitFor,findBy*, event-based sync) instead and rely on global test configs for timeout settings
-
Green Phase: Write MINIMAL code to make the test pass
- Implement only what's needed for the current failing test
- No anticipatory coding or extra features
- Address the specific failure message
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.
- 2mo ago First seen · 103 lines · 13 tokens per session scan A e1b8bfaf1f2e
tdd is a skill published in the GitHub repository wbern/agent-instructions (168 stars, last pushed 5mo ago), licensed MIT. It adds 13 tokens to every session and 1,101 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.
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