Test Doubles Design includes explicit scope boundaries (an explicit 'when not to use' or 'out of scope' section); pricing or quota commentary. At roughly 1,509 words the SKILL.md is on the longer end of the catalog distribution.
Test Doubles Design sits in the Engineering category under the testing sub-topic in the ClaudSkills catalog. There are 10 related skills indexed alongside it; comparing a few before installing usually reveals which fits your workflow best.
These notes are auto-generated from features detected in the SKILL.md file and from this catalog's structure — they aren't part of the source repository.
Test Doubles Design is a community-contributed Claude Code skill in the testing sub-category. It ships as a SKILL.md file that Claude Code auto-discovers under ~/.claude/skills/test-doubles-design/ and loads when your prompt matches the skill's trigger.
When to invoke it: Use when designing or reviewing test doubles — the stand-in objects that replace real collaborators in a test: the five-kind taxonomy (dummy, stub, spy, fake, mock) from Meszaros's xUnit Test Patterns, the difference between state verification (Detroit-school, classicist) and interaction verification (London-school, mockist) and how it determines which doubles fit, the cost of doubles (fragility, false confidence, divergence from real behavior), the role of fakes as the under-used middle ground, the verify_with relationship to test-driven-development, and the heuristics for when to use a real collaborator instead of any double. Do NOT use for choosing test levels or what to test (use testing-strategy), the design discipline of writing tests first (use test-driven-development), specific mocking-library API choice (library docs), or general production stubs and feature flags (use feature-gating or domain-specific skills).
The Test Doubles Design Claude Code skill is built for software engineers, backend developers, full-stack teams, and technical leads building and maintaining production systems. It's part of ClaudSkills (also referred to as Claude Skills or Claude Code Skills) — the open community-curated registry of 146,000+ SKILL.md files for Anthropic's Claude Code agent and the wider Claude ecosystem (Claude API, Claude Agent SDK).
mkdir -p ~/.claude/skills/test-doubles-design curl -L https://claudskills.com/skills/test-doubles-design/SKILL.md \ -o ~/.claude/skills/test-doubles-design/SKILL.md
Or just download SKILL.md directly and drop it into ~/.claude/skills/test-doubles-design/. Claude Code auto-discovers it on next session.
Skills live at ~/.claude/skills/test-doubles-design/SKILL.md on macOS/Linux, or %USERPROFILE%\.claude\skills\test-doubles-design\SKILL.md on Windows. See the full install guide for step-by-step instructions.
Open @claudskills_bot on Telegram, tap Open Desktop App, and the desktop app installs this skill for you. Or share the bot link with a colleague — they get the same one-tap install. Learn more →
The ClaudSkills desktop app installs any skill directly into ~/.claude/skills/ with one click — no terminal required. Pro starts at $9/mo or $149 lifetime.
For the full experience including quality scoring and one-click install features for each skill — upgrade to Pro.
SKILL.md from the source repository to ~/.claude/skills/test-doubles-design/SKILL.md and restart Claude Code. Both flows are detailed at claudskills.com/install/.SKILL.md file that lives under ~/.claude/skills/<name>/ and tells the Claude Code CLI agent how to perform a specific task (instructions, prompts, allowed tools). Skills are auto-discovered at session start. Test Doubles Design is one of 67,000+ skills indexed in the open ClaudSkills catalog, classified under the Engineering category. Learn more at /learn/what-is-a-claude-skill/.If you reference this skill in a blog post, paper, or documentation, you can cite it as:
@misc{test-doubles-design-2026,
author = {jacob-balslev},
title = {Test Doubles Design [Claude Code skill]},
year = {2026},
publisher = {ClaudSkills},
url = {https://claudskills.com/skills/test-doubles-design/}
}Grade A · scanned 2026-07-06 — free static scan against the OWASP Agentic Skills Top 10.
No risk patterns were found in any of the ten OWASP-aligned categories. How grading works ›
Browse all Engineering skills in the ClaudSkills registry, or explore these other picks from the same category:
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SKILL.md files, not affiliated with, endorsed by, or sponsored by Anthropic.