pbt-pragmatic-adoption

pbt-pragmatic-adoption is a skill for Claude Code, Codex from saski/arnesto. It costs 38 tokens per session (1,314 once invoked), scanned A, original, Unlicense.

A practical guide for adding property-based testing to a listings web application monorepo, a repository containing several related projects. Property-based tests generate many inputs to check general rules, or invariants, in unit-tested logic.

In plain words
What is it for?
Use it to review or add unit tests for deterministic filters, parsers, validators, ranking, ordering, mappers, and state calculations.
Why use it?
It helps catch edge cases that a few hand-written examples may miss while keeping the first adoption focused and suitable for continuous integration.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one. Also seen: installed under .agents/ (shared by several agents).

Good fit Use it to review or add unit tests for deterministic filters, parsers, validators, ranking, ordering, mappers, and state calculations.

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Install with agentmods
npx agentmods add skills/saski/arnesto/pbt-pragmatic-adoption
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.

Any agent
npx skills add saski/arnesto --skill pbt-pragmatic-adoption
Clone the repo
git clone --depth 1 https://github.com/saski/arnesto

Made for: Claude Code, Codex.

Wrote 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.

agentmods badge for pbt-pragmatic-adoption

README.md
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Your own site
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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.

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Your own site · 80×15
<a href="https://agentmods.dev/skills/saski/arnesto/pbt-pragmatic-adoption"><img src="https://agentmods.dev/badge/skills/saski/arnesto/pbt-pragmatic-adoption.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 38 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,314 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
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 5.1 $0.00038 $0.01314
Opus 5 $0.00019 $0.00657
Sonnet 5 $0.00008 $0.00263
Haiku 4.5 $0.00004 $0.00131

Measured 7d ago against content hash ef5d274a9c6d, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-11, from the pricing page.

Security

Grade A, and why

pbt-pragmatic-adoption 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 7d 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.

.agents/skills/pbt-pragmatic-adoption/SKILL.md · 126 lines

How it starts

The opening of the file, as written. The whole thing — 126 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Pragmatic PBT Adoption Skill (listings-webapp)

Purpose

Use this skill to find and introduce high-signal property-based tests (PBT) in this repository without destabilizing CI, over-abstracting tests, or replacing clear example-based tests.

Primary goal: strengthen logic-heavy unit tests with a small number of meaningful invariants.

When to use

  • You are reviewing unit test quality in app/, packages/*, or cdk/.
  • You see repeated example-based tests over combinatorial inputs.
  • The code under test is deterministic and mostly pure.
  • You need stronger regression protection for filters, mappers, parsers, validators, ranking, ordering, or state calculations.

When not to use

  • Playwright or browser-flow tests in e2e-tests/.
  • Snapshot-heavy UI rendering assertions.
  • Highly mocked async integration flows where failures are mostly orchestration/network issues.
  • Timezone/clock-sensitive formatting logic unless inputs are tightly constrained and clocks are controlled.

Repository map for PBT decisions

  • app/src/components/**: mostly UI tests; only target pure helper modules.
  • app/src/utils/** and app/src/pages/**/utils.ts: strongest PBT zone.
  • packages/*/src/**: mixed; use PBT for pure format/order helpers, not component rendering.
  • cdk/test/**: infrastructure assertions; PBT usually lower value here.

Good candidate heuristics in this repo

Prefer modules that satisfy most of these:

  • Pure function, deterministic output.
  • No network, no timers, no DOM requirement.
  • Input space is broad (arrays, query params, optional fields, IDs).
  • Existing tests enumerate many examples that encode one invariant.
  • Failure can be explained as business rule breakage.

Strong candidates identified:

  • app/src/utils/arrayUtils.ts
  • app/src/pages/validation/slug.ts
  • app/src/pages/api/[eventId]/utils.ts (hasOnlyDonationTicketsAvailable, hasEarlyBirdTickets, isValidEventId)
  • app/src/components/Body/hooks/useTrackingBeacons/transform.ts
  • app/src/components/MoreOrganizerEvents/utils.ts (getEventsToShow, getMoreEventsFromThisOrganizerFiltered)
  • app/src/components/SEOTags/getBaseDeepLinkAppUrl.ts
  • app/src/utils/correlationId.ts

Read the full file on GitHub · 126 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. 7d ago First seen · 126 lines · 38 tokens per session scan A ef5d274a9c6d

Subscribe to this mod's changes

pbt-pragmatic-adoption is a skill published in the GitHub repository saski/arnesto (5 stars, last pushed today), licensed Unlicense. It adds 38 tokens to every session and 1,314 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 2026-09-03.