Principle Redesign From First Principles
cursor/plugins
Apply when integrating a new requirement into an existing design.
Apply when writing or reviewing tests. An agent skill from jtaroreh/agystack.
MITAuto-check passed
Install Principle Test Behavior Not Implementation
$ npx skills add jtaroreh/agystack --skill principle-test-behavior-not-implementation -a claude-codeProject install by default; add -g for ~/.claude/skills/.
$ gh skill install jtaroreh/agystack principle-test-behavior-not-implementation --agent claude-codeProject scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).
$ git clone --depth 1 https://github.com/jtaroreh/agystack.git skills-src && mkdir -p .claude/skills && cp -r skills-src/skills/principle-test-behavior-not-implementation .claude/skills/principle-test-behavior-not-implementation && rm -rf skills-srcUse ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.
Claude Code skills documentation · loads skills from .claude/skills/
Install the "principle-test-behavior-not-implementation" agent skill from https://github.com/jtaroreh/agystack/tree/main/skills/principle-test-behavior-not-implementation into .claude/skills/principle-test-behavior-not-implementation/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "principle-test-behavior-not-implementation", then confirm the skill loads.Claude Code copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$skill-installer install https://github.com/jtaroreh/agystack/tree/main/skills/principle-test-behavior-not-implementationType this inside Codex. $skill-installer <name> installs a curated skill from openai/skills. The installer writes to $CODEX_HOME/skills (default ~/.codex/skills). Restart Codex if the skill does not show up.
$ npx skills add jtaroreh/agystack --skill principle-test-behavior-not-implementation -a codexProject install goes to .agents/skills/; add -g for ~/.codex/skills/.
$ gh skill install jtaroreh/agystack principle-test-behavior-not-implementation --agent codexProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/jtaroreh/agystack.git skills-src && mkdir -p .agents/skills && cp -r skills-src/skills/principle-test-behavior-not-implementation .agents/skills/principle-test-behavior-not-implementation && rm -rf skills-srcUse ~/.agents/skills/ instead of .agents/skills for a personal install.
Codex skills documentation · loads skills from .agents/skills/
Install the "principle-test-behavior-not-implementation" agent skill from https://github.com/jtaroreh/agystack/tree/main/skills/principle-test-behavior-not-implementation into .agents/skills/principle-test-behavior-not-implementation/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "principle-test-behavior-not-implementation", then confirm the skill loads.Codex copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add jtaroreh/agystack --skill principle-test-behavior-not-implementation -a cursorProject install goes to .agents/skills/; add -g for ~/.cursor/skills/.
$ gh skill install jtaroreh/agystack principle-test-behavior-not-implementation --agent cursorProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/jtaroreh/agystack.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/skills/principle-test-behavior-not-implementation .cursor/skills/principle-test-behavior-not-implementation && rm -rf skills-srcUse ~/.cursor/skills/ instead of .cursor/skills for a personal install.
Cursor skills documentation · loads skills from .cursor/skills/, .agents/skills/, .claude/skills/, .codex/skills/
Install the "principle-test-behavior-not-implementation" agent skill from https://github.com/jtaroreh/agystack/tree/main/skills/principle-test-behavior-not-implementation into .cursor/skills/principle-test-behavior-not-implementation/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "principle-test-behavior-not-implementation", then confirm the skill loads.Cursor copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gemini skills install https://github.com/jtaroreh/agystack.git --path skills/principle-test-behavior-not-implementation--scope user (default) or --scope workspace; --path is the subfolder of the repo that holds the skill; --consent skips the security confirmation prompt.
$ npx skills add jtaroreh/agystack --skill principle-test-behavior-not-implementation -a gemini-cliProject install goes to .agents/skills/; add -g for ~/.gemini/skills/.
$ gh skill install jtaroreh/agystack principle-test-behavior-not-implementation --agent gemini-cliProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/jtaroreh/agystack.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/skills/principle-test-behavior-not-implementation .gemini/skills/principle-test-behavior-not-implementation && rm -rf skills-srcUse ~/.gemini/skills/ instead of .gemini/skills for a personal install, then run /skills reload.
Gemini CLI skills documentation · loads skills from .gemini/skills/, .agents/skills/
Install the "principle-test-behavior-not-implementation" agent skill from https://github.com/jtaroreh/agystack/tree/main/skills/principle-test-behavior-not-implementation into .gemini/skills/principle-test-behavior-not-implementation/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "principle-test-behavior-not-implementation", then confirm the skill loads.Gemini CLI copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gh skill install jtaroreh/agystack principle-test-behavior-not-implementationInstalls for Copilot at project scope by default; add --scope user for a personal install. Preview a skill first with gh skill preview. Needs GitHub CLI 2.90.0 or later (public preview).
$ npx skills add jtaroreh/agystack --skill principle-test-behavior-not-implementation -a github-copilotProject install goes to .agents/skills/; add -g for ~/.copilot/skills/.
$ git clone --depth 1 https://github.com/jtaroreh/agystack.git skills-src && mkdir -p .github/skills && cp -r skills-src/skills/principle-test-behavior-not-implementation .github/skills/principle-test-behavior-not-implementation && rm -rf skills-srcUse ~/.copilot/skills/ instead of .github/skills for a personal install. Commit .github/skills so cloud agent and code review can use it.
GitHub Copilot skills documentation · loads skills from .github/skills/, .claude/skills/, .agents/skills/
Install the "principle-test-behavior-not-implementation" agent skill from https://github.com/jtaroreh/agystack/tree/main/skills/principle-test-behavior-not-implementation into .github/skills/principle-test-behavior-not-implementation/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "principle-test-behavior-not-implementation", then confirm the skill loads.GitHub Copilot copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add jtaroreh/agystack --skill principle-test-behavior-not-implementation -a opencodeOpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.
$ gh skill install jtaroreh/agystack principle-test-behavior-not-implementation --agent opencodeProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/jtaroreh/agystack.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/skills/principle-test-behavior-not-implementation .opencode/skills/principle-test-behavior-not-implementation && rm -rf skills-srcUse ~/.config/opencode/skills/ instead of .opencode/skills for a personal install.
OpenCode skills documentation · loads skills from .opencode/skills/, .claude/skills/, .agents/skills/
Install the "principle-test-behavior-not-implementation" agent skill from https://github.com/jtaroreh/agystack/tree/main/skills/principle-test-behavior-not-implementation into .opencode/skills/principle-test-behavior-not-implementation/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "principle-test-behavior-not-implementation", then confirm the skill loads.OpenCode copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
Facts
- Skill name
principle-test-behavior-not-implementation- GitHub stars
- 108
- Token cost
- ~416 tokens
- SKILL.md length
- 186 words
- Files
- 1
- Skills in repo
- 6
- Repo updated
- First seen
- Licence
- MIT
At a glance
Apply when writing or reviewing tests. An agent skill from jtaroreh/agystack.
- Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md
What it does
Principle Test Behavior Not Implementation is an agent skill from jtaroreh/agystack. Apply when writing or reviewing tests. Test what the system does from the outside (inputs, outputs, observable behavior, invariants), not how it is structured internally (private methods, call counts, internal state).
Its SKILL.md is about 420 tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts.
The repository describes itself as: Closed-loop engineering workflow and agentic swarm orchestration plugin for Google Antigravity. The licence is MIT.
Example prompts
- “/principle-test-behavior-not-implementation”
What it can do on your machine
Read from SKILL.md and the folder at commit d1a0466. It shows what the files ask for, not the result of running them.
Tool permissions
Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.
From allowed-tools in the SKILL.md frontmatter.
Runs code
No scripts in the folder and no shell commands in SKILL.md.
From the folder's file list and the shell code blocks in SKILL.md.
Network
No URLs in SKILL.md.
From URLs in SKILL.md, links to its own repository left out.
Credentials
Names no API keys, tokens, secrets or passwords.
From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.
Context cost
Principle Test Behavior Not Implementation loads about 416 tokens when it runs. Until then it costs about 65 tokens; SKILL.md has 186 words of instructions outside code blocks.
Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.
Safety
Auto-check passed
The automated check found no risky patterns in SKILL.md.
Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.
SKILL.md
The full file from jtaroreh/agystack at commit d1a0466, republished under its MIT licence (© jtaroreh). 186 words, ~416 tokens.
Download SKILL.mdSave it as
.claude/skills/principle-test-behavior-not-implementation/SKILL.md (or your agent's skills folder).- name
- principle-test-behavior-not-implementation
- description
- Apply when writing or reviewing tests. Test what the system does from the outside (inputs, outputs, observable behavior, invariants), not how it is structured internally (private methods, call counts, internal state).
- disable-model-invocation
- true
Test Behavior, Not Implementation
Write tests against observable behavior and contracts, not internal implementation details. Tests should survive refactoring without changes.
Why: Tests coupled to internal details (mocking internal methods, asserting specific call counts, inspecting private state) break when code is refactored, even when behavior is unchanged. This creates test maintenance burden and discourages refactoring.
Pattern: Ask: "If I rewrote the internals completely, would this test still pass?"
Good tests:
- Treat the unit or subsystem as a black box with defined inputs and outputs.
- Test contracts, invariants, and edge cases.
- Use public APIs and observable side effects.
- Verify state through public query methods or final output artifacts.
Avoid:
- Mocking functions you own (prefer real instances or lightweight fakes).
- Asserting on internal call counts or execution order when order is not part of the contract.
- Asserting on exact internal data structures rather than the public result.
- Writing tests that duplicate the implementation logic.
Refactoring test:
- If changing internal implementation breaks tests while the feature still works, the tests were testing implementation, not behavior.
- Rewrite the brittle tests to assert on public outcomes before proceeding with the refactor.
© jtaroreh, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file
Files
Just SKILL.md in skills/principle-test-behavior-not-implementation of jtaroreh/agystack.
Open the folder on GitHubat commit d1a0466
Compare with similar skills
Principle Test Behavior Not Implementation next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.
| Skill | Stars | Used in | Tokens | Auto-check | Licence | Repo updated |
|---|---|---|---|---|---|---|
| Principle Test Behavior Not Implementation this skilljtaroreh/agystack | 108 | — | ~416 | Automated safety check: Pass | MIT | |
| Principle Redesign From First Principlescursor/plugins | 10k | 8 repos | ~211 | Automated safety check: Pass | None | |
| Uxui Principlessickn33/agentic-awesome-skills | 47k | 2 repos | ~548 | Automated safety check: Pass | MIT | |
| First Principles Thinkingmindfold-ai/Trellis | 15k | — | ~4.1k | Automated safety check: Pass | MIT | |
| Editorial Burgundy Principles Templatenexu-io/open-design | 100k | — | ~461 | Automated safety check: Pass | Apache-2.0 | |
| Design PrinciplesOwl-Listener/designer-skills | 2.9k | 1 repos | ~300 | Automated safety check: Pass | MIT |
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Questions about Principle Test Behavior Not Implementation
What does Principle Test Behavior Not Implementation do?
Apply when writing or reviewing tests. An agent skill from jtaroreh/agystack. Principle Test Behavior Not Implementation is an agent skill from jtaroreh/agystack. Apply when writing or reviewing tests.
How do I install Principle Test Behavior Not Implementation in Claude Code?
Run `npx skills add jtaroreh/agystack --skill principle-test-behavior-not-implementation -a claude-code`. Or copy the skill folder (skills/principle-test-behavior-not-implementation in jtaroreh/agystack) into .claude/skills/principle-test-behavior-not-implementation in your project. Claude Code loads it when a task matches its description.
How do I install Principle Test Behavior Not Implementation in Codex?
Run `npx skills add jtaroreh/agystack --skill principle-test-behavior-not-implementation -a codex`. Or copy the skill folder (skills/principle-test-behavior-not-implementation in jtaroreh/agystack) into .agents/skills/principle-test-behavior-not-implementation in your project. Codex loads it when a task matches its description.
Can I use Principle Test Behavior Not Implementation in Cursor, Gemini CLI or GitHub Copilot?
Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add jtaroreh/agystack --skill principle-test-behavior-not-implementation -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/principle-test-behavior-not-implementation, .gemini/skills/principle-test-behavior-not-implementation, .github/skills/principle-test-behavior-not-implementation and .opencode/skills/principle-test-behavior-not-implementation in your project.
What does Principle Test Behavior Not Implementation need to run?
SKILL.md names no scripts, command-line tools or credentials: Principle Test Behavior Not Implementation is instructions for the agent only.
Does Principle Test Behavior Not Implementation access the network?
SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.
Is Principle Test Behavior Not Implementation safe to install?
Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.
What licence does Principle Test Behavior Not Implementation use?
Principle Test Behavior Not Implementation is published under the MIT licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.
How many tokens does Principle Test Behavior Not Implementation use?
About 416 tokens (SKILL.md is roughly 1.7k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.
What are the alternatives to Principle Test Behavior Not Implementation?
Skills that share tags, products or a category with Principle Test Behavior Not Implementation: Principle Redesign From First Principles (cursor/plugins, 10k stars), Uxui Principles (sickn33/agentic-awesome-skills, 47k stars), First Principles Thinking (mindfold-ai/Trellis, 15k stars) and Editorial Burgundy Principles Template (nexu-io/open-design, 100k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.
Who maintains Principle Test Behavior Not Implementation?
jtaroreh (a GitHub user) maintains it in jtaroreh/agystack, which has 108 GitHub stars. The repository holds 6 skills in this directory. The repository was last updated on October 1, 2026.
Source: jtaroreh/agystack on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.