tdd

A test-driven development guide for fixing bugs. TDD means writing a test that shows the bug before changing the code, then confirming the test passes after the fix.

In plain words
What is it for?
Use it for bugs with a clear, inexpensive test path, especially when adding a focused regression test would verify the fix.
Why use it?
It turns a bug report into a repeatable check and helps prevent the same problem from returning. It skips new tests when testing would require impractical setup.

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

Made for: Claude Code, Codex.

Per session 52 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 683 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 $0.00052 $0.00683
Opus 5 $0.00026 $0.00342
Sonnet 5 $0.00010 $0.00137
Haiku 4.5 $0.00005 $0.00068

Measured yesterday against content hash b4df402c414c, 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 yesterday.

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 — 1 line 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.

.opencode/skills/tdd/SKILL.md · 44 lines

How it starts

The opening of the file, as written. The whole thing — 44 lines — stays where its author put it; the contents beside it link to each section on GitHub.

TDD Bug Fix

When fixing a bug with a clear, cheap test path, make the broken behavior executable before changing production code. The goal is a focused regression test that fails before the fix and passes after it.

Do not force a test when it would be impractical. If the available test would require broad harness setup, brittle mocks, slow end-to-end infrastructure, production-only state, vague reproduction steps, or large unrelated fixture churn, skip adding a new test and use the closest useful verification instead.

Workflow

  1. Understand the bug. Identify the intended behavior, current behavior, affected path, and smallest observable reproduction.
  2. Choose the narrowest executable check. Prefer the closest unit, component, integration, or regression test already used for that codepath. If no practical test path is obvious, do not create one from scratch just to satisfy the workflow.
  3. Write the failing test first. Add the smallest focused test that would have caught the bug. The test should encode intended behavior, not mirror the current implementation.
  4. Run the new test before fixing. Confirm it fails for the intended reason. If it passes or fails for an unrelated reason, correct the test or reproduction before editing the implementation.
  5. Fix the bug. Make the smallest production change that satisfies the intended behavior while preserving nearby contracts.
  6. Rerun the regression test. Confirm the test now passes.
  7. Run nearby validation. Run relevant adjacent tests, type checks, lint, or scenario checks when the change has broader risk.

If a Failing Test Is Impractical

Do not silently skip the regression step. Before fixing, explicitly explain why a failing test is impossible or not worth the cost, then choose the closest executable regression check available. Examples include a targeted script, manual reproduction command, browser automation, snapshot comparison, log assertion, or focused integration check.

Read the full file on GitHub · 44 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. yesterday First seen · 44 lines · 52 tokens per session scan A b4df402c414c

Subscribe to this mod's changes

tdd is a skill published in the GitHub repository painhardcore/pstack (1 stars, last pushed 5d ago), licensed MIT. It adds 52 tokens to every session and 683 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. It is 98% identical to tdd, differing in 1 line, and is treated as a copy.

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