tdd

A development method called test-driven development, or TDD, where you write a failing test, add the smallest code that passes it, and then improve the code. It applies this red-green-refactor cycle across the application.

In plain words
What is it for?
Use it to build domain logic and application or infrastructure behavior from tests, with optional acceptance tests for complete use cases and a required coverage target.
Why use it?
It makes expected behavior explicit before implementation and helps detect regressions as the code changes.

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/fmflurry/settings-opencode/tdd
Any agent
npx skills add fmflurry/settings-opencode --skill tdd
Clone the repo
git clone --depth 1 https://github.com/fmflurry/settings-opencode

Made for: Claude Code, Codex.

Per session 107 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 3,783 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 $0.00107 $0.03783
Opus 5 $0.00053 $0.01892
Sonnet 5 $0.00021 $0.00757
Haiku 4.5 $0.00011 $0.00378

Measured 2d ago against content hash ddf2ac9ac245, 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/skills/tdd/SKILL.md · 249 lines

How it starts

The opening of the file, as written. The whole thing — 249 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Test-Driven Development — RED-GREEN-REFACTOR (mandatory baseline + optional ATDD outer loop)

The Core Mandate: RED-GREEN-REFACTOR

Features are built via strict TDD discipline: every behavior emerges via a failing test, minimal production code makes it green, then refactor while tests stay green. Tests and production code never change in the same commit. Hardcoding/faking is expected in the green step, then triangulated away during refactoring or by new tests.

This discipline applies to all layers: domain aggregates, Application handlers, Infrastructure implementations.

Optional: Double-Loop Method (ATDD Outer Loop)

For explicit use-case specification, you may adopt a two-loop structure: the outer loop turns a specification into acceptance tests at the handler level (Application layer); the inner loop builds domain behavior via strict RED-GREEN-REFACTOR. The outer loop helps document and test integration points; it is not mandatory.

OPTIONAL OUTER (ATDD): write the WHOLE shopping list of stub acceptance tests (all scenarios)
                                              │
                                              ▼  then, one stub at a time:
              flesh stub into real red test ──► create Application artifacts ──► still red
                                              │
                                              ▼  domain behavior missing?
                            INNER (TDD): red ─► green ─► refactor   (repeat)
                                              │
                                              ▼
                       acceptance test goes green ─► refactor ─► next stub ─► … ─► done


MANDATORY (all features, all layers):
              write test ─► compile shells ─► green code ─► refactor ──┐
                                                                       └─► next behavior

Input: Specification

Before writing any test, a specification exists. It may come from:

  • OpenSpec change spec (openspec/changes/<change>/specs/<capability>/spec.md) with #### Scenario: WHEN/THEN blocks.
  • Product Owner work item (issue, backlog story, design doc) enumerating scenarios and examples.
  • Finalized use-case documentation in docs/usecases/<context>/ (less common going forward; prefer OpenSpec).

Read the full file on GitHub · 249 lines

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 · 249 lines · 0 tokens per session scan A ddf2ac9ac245

Subscribe to this mod's changes

tdd is a skill published in the GitHub repository fmflurry/settings-opencode (172 stars, last pushed 20d ago), licensed MIT. It adds 107 tokens to every session and 3,783 once invoked, about $0.0005 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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