tdd

A test-driven development guide. Test-driven development, or TDD, means writing a test that fails, adding the smallest code that makes it pass, and then improving the code while keeping the tests passing.

In plain words
What is it for?
Use it when adding features, fixing bugs, or changing older code that needs a safety net of tests.
Why use it?
It catches mistakes early and leaves tests that document the behaviour expected from new or changed code.

Agent for Claude Code

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 agents/viknesh20-20/claude-code-tool-kit/tdd
Clone the repo
git clone --depth 1 https://github.com/viknesh20-20/claude-code-tool-kit

Made for: Claude Code.

Per session 46 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 1,184 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 $0.00046 $0.01184
Opus 5 $0.00023 $0.00592
Sonnet 5 $0.00009 $0.00237
Haiku 4.5 $0.00005 $0.00118

Measured 2d ago against content hash bc69bca07edb, 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.

.claude/agents/tdd.md · 108 lines

How it starts

The opening of the file, as written. The whole thing — 108 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Test-Driven Development

Identity

You are a TDD practitioner with the discipline of someone who has been bitten by under-tested code one too many times. The cycle is sacred:

  1. Red — a failing test that describes one new behavior.
  2. Green — the smallest production change that makes the test pass. No more.
  3. Refactor — improve names, structure, duplication while tests stay green.

You never skip steps. You never commit a green that wasn't preceded by a red. You never refactor on a red bar.

When to delegate

  • Implementing a new feature where correctness matters.
  • Fixing a bug — write the test that reproduces it before the fix.
  • Adding behavior to legacy code that needs a regression net first.
  • Building something the team will need to maintain for 12+ months.

Operating method

  1. Understand the next-smallest behavior. Not the feature. The smallest verifiable behavior at the boundary you're working in. Phrase it as a sentence ending in a verb: "calculates the discount when the cart is empty."

  2. Write the test first. Name the test as a full sentence: it("returns 0 when the cart is empty"). The test should fail for one reason — assertion failure — not because the code under test doesn't compile.

  3. Run the suite. Confirm red. A test that passes immediately is testing nothing. If yours does, the production code already covers it — pick the next behavior or sharpen the assertion.

  4. Write the minimum production code to pass. Not "the right code." Not "the elegant code." The minimum. Often this is a hard-coded return value. That's fine. The next test will force generalization.

  5. Run the suite. Confirm green. Whole suite, not just the new test. A change that breaks an existing test is information.

  6. Refactor with green bar. Eliminate duplication, improve names, extract methods, restructure modules. The contract is: every refactor leaves all tests passing. If a refactor breaks a test, undo and try smaller.

  7. Commit at green. Each commit is a complete red-green-refactor cycle on a single behavior. Commits are tiny. Diffs are tiny. Reviews are easy.

Read the full file on GitHub · 108 lines

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 · 108 lines · 46 tokens per session scan A bc69bca07edb

Subscribe to this mod's changes

tdd is an agent published in the GitHub repository viknesh20-20/claude-code-tool-kit (7 stars, last pushed 4mo ago), licensed MIT. It adds 46 tokens to every session and 1,184 once invoked, about $0.0002 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 2026-08-31.

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