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principle-test-behavior-not-implementation

principle-test-behavior-not-implementation is a skill for Claude Code, Codex from edlng/agents. It costs 50 tokens per session (540 once invoked), scanned A, original, no licence file.

A testing rule that checks software through the way its users call it and verifies the exact result they should see. It avoids tests that only check internal implementation details.

In plain words
What is it for?
Use it when writing, changing, or deciding whether to keep a test, especially when choosing assertions.
Why use it?
It prevents tests from passing while the user-facing behaviour is broken or while imported functions return no meaningful result.

Skill for Claude CodeCodex

Which agent this was written for is unclear — body not stored (licence); the path alone says nothing.

not rated 2repo changed 14d ago A scan 50 tokens no licence

Good fit Use it when writing, changing, or deciding whether to keep a test, especially when choosing assertions.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/edlng/agents/principle-test-behavior-not-implementation
View source ↗ edlng/agents edlng.github.io
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 edlng/agents --skill principle-test-behavior-not-implementation
Clone the repo
git clone --depth 1 https://github.com/edlng/agents

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 principle-test-behavior-not-implementation

README.md
[![agentmods](https://agentmods.dev/badge/skills/edlng/agents/principle-test-behavior-not-implementation/github.svg)](https://agentmods.dev/skills/edlng/agents/principle-test-behavior-not-implementation)
Your own site
<a href="https://agentmods.dev/skills/edlng/agents/principle-test-behavior-not-implementation"><img src="https://agentmods.dev/badge/skills/edlng/agents/principle-test-behavior-not-implementation/github.svg" alt="Measured on agentmods" height="20"></a>

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.

agentmods 80×15 button for principle-test-behavior-not-implementation

Your own site · 80×15
<a href="https://agentmods.dev/skills/edlng/agents/principle-test-behavior-not-implementation"><img src="https://agentmods.dev/badge/skills/edlng/agents/principle-test-behavior-not-implementation.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 50 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 540 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 unknown 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 $0.00050 $0.00540
Opus 5.5 $0.00020 $0.00216
Sonnet 5.5 $0.00010 $0.00108
Haiku 4.5 $0.00005 $0.00054

Measured 14d ago against content hash 0d1092aefb21, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

principle-test-behavior-not-implementation 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 14d 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/universal/principle-test-behavior-not-implementation/SKILL.md · 20 lines

The source is not reproduced here

No licence file

A repository with no LICENSE is all rights reserved by default, so the body is not copied here. The metadata, the measurements and the link are.

Read it on GitHub

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. 14d ago Changed · -7 lines · -13 tokens per session 0d1092aefb21
  2. 1mo ago First seen · 27 lines · 63 tokens per session scan A dd4631068333

Subscribe to this mod's changes

principle-test-behavior-not-implementation is a skill published in the GitHub repository edlng/agents (2 stars, last pushed 8d ago), with no licence file. It adds 50 tokens to every session and 540 once invoked, about $0.0002 per session on Opus 5.5. 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 2026-10-06.

Testing
Related

principle-test-behavior-not-implementation compared with skills from other repositories

principle-test-behavior-not-implementation next to 6 skills from other repositories
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principle-test-behavior-not-implementationedlng/agentsSkill28d agononeA50Claude Code, Codex
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playwright-climicrosoft/playwrightSkill99ktodayApache-2.0A19Claude Code
local-ai-agentsmicrosoft/ai-agents-for-beginnersSkill79ktodayMITA200Claude Code, Codex
systematic-debuggingobra/superpowersSkill314k3d agoMITA21Claude Code
next-cache-components-adoptionvercel/next.jsSkill143kyesterdayMITA95Claude Code
next-partial-prefetching-adoptionvercel/next.jsSkill143kyesterdayMITA103Claude Code