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Agent skill

Python Mock Isolation Design

by hashgraph-online in hashgraph-online/awesome-codex-plugins

Use Python mocks and fakes as a design tool without losing behavioral confidence.

MITAuto-check passedDevelopment

Install Python Mock Isolation Design

skills CLI
$ npx skills add hashgraph-online/awesome-codex-plugins --skill python-mock-isolation-design -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI
$ gh skill install hashgraph-online/awesome-codex-plugins python-mock-isolation-design --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy
$ git clone --depth 1 https://github.com/hashgraph-online/awesome-codex-plugins.git skills-src && mkdir -p .claude/skills && cp -r skills-src/plugins/LVTD-LLC/skills/skills/python-mock-isolation-design .claude/skills/python-mock-isolation-design && rm -rf skills-src

Use ~/.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/

Facts

Skill name
python-mock-isolation-design
GitHub stars
1.2k
Token cost
~877 tokens
SKILL.md length
394 words
Files
4 (incl. references)
Skills in repo
736
Repo updated
First seen
Licence
MIT

At a glance

Use Python mocks and fakes as a design tool without losing behavioral confidence.

  • Works in 4 steps: Name the boundary. → Choose the replacement. → Keep behavior assertions primary. → …
  • Testing external dependencies
  • SKILL.md covers Source Traceability, Workflow, Decision Rules and Guardrails, plus 1 more section
  • Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md

What it does

Python Mock Isolation Design is an agent skill from hashgraph-online/awesome-codex-plugins. Use Python mocks and fakes as a design tool without losing behavioral confidence. Use when testing external dependencies, choosing monkeypatch versus unittest.mock.patch, isolating slow boundaries, avoiding mock-heavy tests, interpreting mock call assertions, or refactoring toward clearer dependency seams.

Its SKILL.md is about 880 tokens, which your agent loads only when the skill is triggered. The skill folder holds 6 other files, including reference files (for example `agents/openai.yaml`, `evals/evals.json` and `references/mock-isolation-patterns.md`). Compatibility notes: Codex, Claude Code, and other Agent Skills-compatible clients.

It sits in Development, covering Refactoring. It works with Python. The repository describes itself as: A curated list of awesome OpenAI Codex / ChatGPT plugins, skills, and resources. The 1 Codex Marketplace. See live plugins at: https://hol.org/plugins/best-codex-plugins. The licence is MIT.

When your agent uses it

  • Testing external dependencies
  • Choosing monkeypatch versus unittest.mock.patch
  • Isolating slow boundaries
  • Avoiding mock-heavy tests

Example prompts

  • “/python-mock-isolation-design”

Requirements

  • Python 3
  • Compatibility (from SKILL.md): Codex, Claude Code, and other Agent Skills-compatible clients.

Workflow steps

4 steps, taken from the first numbered list in SKILL.md.

  1. Name the boundary.
  2. Choose the replacement.
  3. Keep behavior assertions primary.
  4. Watch for design feedback.

What it can do on your machine

Read from SKILL.md and the folder at commit 16b4156. 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.

  • Compatibility

    Codex, Claude Code, and other Agent Skills-compatible clients.

    From compatibility in the SKILL.md frontmatter.

Context cost

Python Mock Isolation Design loads about 877 tokens when it runs, and up to ~1.4k if it reads all its reference files. Until then it costs about 84 tokens; SKILL.md has 394 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~84
When it runs · the whole SKILL.md, loaded when a task matches
~877
With references · SKILL.md plus every file in references/, read only if the agent opens them
~1.4k

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 hashgraph-online/awesome-codex-plugins at commit 16b4156, republished under its MIT licence (© hashgraph-online). 394 words, ~877 tokens.

Download SKILL.mdSave it as .claude/skills/python-mock-isolation-design/SKILL.md (or your agent's skills folder). This skill also uses 3 other files; get the full folder from GitHub.
name
python-mock-isolation-design
description
Use Python mocks and fakes as a design tool without losing behavioral confidence. Use when testing external dependencies, choosing monkeypatch versus unittest.mock.patch, isolating slow boundaries, avoiding mock-heavy tests, interpreting mock call assertions, or refactoring toward clearer dependency seams.
compatibility
Codex, Claude Code, and other Agent Skills-compatible clients.
license
MIT
metadata.version
0.1.0
metadata.displayName
Python Mock Isolation Design
metadata.category
Testing
metadata.tags
python,tdd,testing,mocking,architecture

Python Mock Isolation Design

Use this skill when replacing a dependency in a Python test changes what the test proves. Mocks are useful at slow, nondeterministic, or external boundaries; they become harmful when they replace the behavior the test is supposed to validate.

Source Traceability

Primary source: Harry Percival, Test-Driven Development with Python, 3rd ed. Guidance is transformed and paraphrased from chapters 20, 21, 27, and Appendix A, especially manual monkeypatching, unittest.mock.patch, mock coupling, call argument inspection, test isolation, and the architectural route out of mock-heavy suites.

Workflow

  1. Name the boundary.

    • External service, email, clock, filesystem, network, framework adapter, or expensive side effect.
    • If the dependency is local domain logic, prefer real code.

  2. Choose the replacement.

    • Use a fake when state and behavior are simple and meaningful.
    • Use patch when replacing a collaborator looked up by the module under test.
    • Use monkeypatching sparingly and restore state automatically.
    • Use autospec/spec when interface drift matters.

  3. Keep behavior assertions primary.

    • Assert user-visible or domain-visible outcomes first.
    • Assert mock calls only when the interaction is the contract.
    • Inspect call arguments when they clarify the behavior, not as a substitute for it.

  4. Watch for design feedback.

    • If setup requires many mocks, the code may have hidden dependencies.
    • If tests break on harmless refactors, the test is too coupled to implementation.
    • Consider introducing a boundary interface, service object, or functional core.

Read mock-isolation-patterns.md for replacement choices and smell handling.

Show full SKILL.md (157 more words)Show less

Decision Rules

  • Patch where the code under test looks up the dependency.
  • Prefer fakes for small stable protocols.
  • Use mock.return_value and side_effect deliberately; do not let default mocks create imaginary object graphs.
  • Avoid broad MagicMock objects without specs for important interfaces.
  • Keep at least one integration or contract test for each important boundary.

Guardrails

  • Do not mock Django settings, HTTP, time, or command output by hand if a framework helper exists; use django-targeted-mocking for Django-specific boundaries.
  • Do not assert only that a mocked method was called unless that call is the behavior.
  • Do not use mocks as the primary strategy for making all tests fast; architecture should carry that work.
  • Do not keep mocks that prevent refactoring from changing implementation safely.

Verification

Before finishing, record:

  • Boundary being replaced and why.
  • Fake, patch, or real dependency choice.
  • Behavior assertion that proves the outcome.
  • Mock interaction assertion only when interaction is the contract.
  • Integration/contract coverage for the real boundary.

© hashgraph-online, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

SKILL.md and 3 other files (references) in plugins/LVTD-LLC/skills/skills/python-mock-isolation-design of hashgraph-online/awesome-codex-plugins.

  • SKILL.md
  • agents/openai.yaml
  • evals/evals.json
  • references/mock-isolation-patterns.md

Open the folder on GitHubat commit 16b4156

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Works with

Categories

Questions about Python Mock Isolation Design

What does Python Mock Isolation Design do?

Use Python mocks and fakes as a design tool without losing behavioral confidence. Python Mock Isolation Design is an agent skill from hashgraph-online/awesome-codex-plugins. Use Python mocks and fakes as a design tool without losing behavioral confidence.

When should I use Python Mock Isolation Design?

Python Mock Isolation Design fits situations like: testing external dependencies; choosing monkeypatch versus unittest.mock.patch; isolating slow boundaries; avoiding mock-heavy tests.

How do I install Python Mock Isolation Design in Claude Code?

Run `npx skills add hashgraph-online/awesome-codex-plugins --skill python-mock-isolation-design -a claude-code`. Or copy the skill folder (plugins/LVTD-LLC/skills/skills/python-mock-isolation-design in hashgraph-online/awesome-codex-plugins) into .claude/skills/python-mock-isolation-design in your project. Claude Code loads it when a task matches its description.

How do I install Python Mock Isolation Design in Codex?

Run `npx skills add hashgraph-online/awesome-codex-plugins --skill python-mock-isolation-design -a codex`. Or copy the skill folder (plugins/LVTD-LLC/skills/skills/python-mock-isolation-design in hashgraph-online/awesome-codex-plugins) into .agents/skills/python-mock-isolation-design in your project. Codex loads it when a task matches its description.

Can I use Python Mock Isolation Design 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 hashgraph-online/awesome-codex-plugins --skill python-mock-isolation-design -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/python-mock-isolation-design, .gemini/skills/python-mock-isolation-design, .github/skills/python-mock-isolation-design and .opencode/skills/python-mock-isolation-design in your project.

What does Python Mock Isolation Design need to run?

SKILL.md names no scripts, command-line tools or credentials: Python Mock Isolation Design is instructions for the agent only. Our summary lists: Python 3. Compatibility (from SKILL.md): Codex, Claude Code, and other Agent Skills-compatible clients..

Does Python Mock Isolation Design 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 Python Mock Isolation Design 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 Python Mock Isolation Design use?

Python Mock Isolation Design is published under the MIT licence (declared in SKILL.md). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does Python Mock Isolation Design use?

About 877 tokens (SKILL.md is roughly 3.5k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full. Its references folder adds about 560 tokens, read only when the agent opens those files.

What are the alternatives to Python Mock Isolation Design?

Skills that share tags, products or a category with Python Mock Isolation Design: Dignified Python Standards (docling-project/docling, 68k stars), Readable Py (crazyguitar/pysheeet, 8.2k stars), Nexus Mapper (Haaaiawd/Nexus-skills, 166 stars) and Refactor Op (CVCUDA/CV-CUDA, 2.7k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Python Mock Isolation Design?

hashgraph-online (a GitHub organization) maintains it in hashgraph-online/awesome-codex-plugins, which has 1,232 GitHub stars. The repository holds 736 skills in this directory. The repository was last updated on October 6, 2026.

Source: hashgraph-online/awesome-codex-plugins on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.