What is test-case-coach?

A coach for designing a small, meaningful test suite after you have an algorithm or implementation. It focuses on input groups, boundary values, and cases that challenge your assumptions.

Use it to choose representative inputs, find missing or adversarial cases, and predict the expected result for every selected test.

It helps you understand why each test matters instead of copying a long list of unrelated edge cases.

test-case-coach — Skill for Claude Code and Codex by Far-200: A coach for designing a small, meaningful test suite…

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/far-200/think-before-code/test-case-coach

Any agent

npx skills add Far-200/think-before-code --skill test-case-coach

Clone the repo

git clone --depth 1 https://github.com/Far-200/think-before-code

Made for: Claude Code, Codex.

Per session 102 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 2,416 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.

Model	Per session	Once invoked
Fable 5	$0.00102	$0.02416
Opus 5	$0.00051	$0.01208
Sonnet 5	$0.00020	$0.00483
Haiku 4.5	$0.00010	$0.00242

Measured 3d ago against content hash 552aac2ad75a, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

test-case-coach 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 3d 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.

skills/test-case-coach/SKILL.md · 256 lines

How it starts

The opening of the file, as written. The whole thing — 256 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Test Case Coach

Why this exists

Left alone, an LLM asked "what should I test?" produces a wall of thirty edge cases in one response. The learner copies them, runs them, and learns nothing about why those cases matter or how to find the next set themselves. The list is complete; the skill it was supposed to build never forms.

This skill exists to make the learner design the suite: partition the input space, pick boundary representatives, attack their own assumptions, and predict every expected output — one dimension at a time, with a justification attached to every case that survives.

Boundary with neighboring skills

vs. problem-decoder — reading the edge cases a problem statement implies before any solving happens is decoding. This skill starts later: the learner already has an approach or code, and the question is which concrete, executable inputs would meaningfully exercise it.
vs. dry-run-coach — dry-run-coach traces one selected input through explicit state, step by step. This skill decides which inputs deserve that attention in the first place. Once a case is chosen and needs a full trace, that's dry-run-coach's discipline.
vs. debug-coach — the moment a designed case actually fails — a concrete input with a concrete expected-vs-actual mismatch — this skill's job is done for that input. Hand off to debug-coach with the failing case; don't start diagnosing here. In the other direction, a bug debug-coach has fixed leaves behind a smallest failing input, which belongs in the suite as a regression case.
vs. dsa-tutor — no approach yet means nothing to test yet. Send the learner to dsa-tutor first.
vs. specification-coach — observable acceptance criteria for a feature that hasn't been built are part of defining it, not a test suite. This skill needs an approach or implementation to design executable cases against; before that exists, the criteria belong to specification-coach.
vs. complexity-coach — a degenerate input chosen to check Big-O behavior is complexity-coach's stress test, not a correctness test in this suite.

Read the full file on GitHub · 256 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.

3d ago First seen · 256 lines · 102 tokens per session scan A 552aac2ad75a

Subscribe to this mod's changes

test-case-coach is a skill published in the GitHub repository Far-200/think-before-code (8 stars, last pushed 18d ago), licensed MIT. It adds 102 tokens to every session and 2,416 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 2026-08-31.

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