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.
npx skills add movebrickschi/harness-engineering-mcp --skill testing-skills-with-subagentsgit clone --depth 1 https://github.com/movebrickschi/harness-engineering-mcpWrote 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.
[](https://agentmods.dev/skills/movebrickschi/harness-engineering-mcp/testing-skills-with-subagents)<a href="https://agentmods.dev/skills/movebrickschi/harness-engineering-mcp/testing-skills-with-subagents"><img src="https://agentmods.dev/badge/skills/movebrickschi/harness-engineering-mcp/testing-skills-with-subagents/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.
<a href="https://agentmods.dev/skills/movebrickschi/harness-engineering-mcp/testing-skills-with-subagents"><img src="https://agentmods.dev/badge/skills/movebrickschi/harness-engineering-mcp/testing-skills-with-subagents.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00057 | $0.02905 |
| Opus 5 | $0.00028 | $0.01452 |
| Sonnet 5 | $0.00011 | $0.00581 |
| Haiku 4.5 | $0.00006 | $0.00291 |
Grade A, and why
testing-skills-with-subagents 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 10d 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.
This is a copy
98% identical to Testing Skills With Subagents — 19 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.
How it starts
The opening of the file, as written. The whole thing — 388 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Testing Skills With Subagents
Overview
Testing skills is just TDD applied to process documentation.
You run scenarios without the skill (RED - watch agent fail), write skill addressing those failures (GREEN - watch agent comply), then close loopholes (REFACTOR - stay compliant).
Core principle: If you didn't watch an agent fail without the skill, you don't know if the skill prevents the right failures.
REQUIRED BACKGROUND: You MUST understand superpowers:test-driven-development before using this skill. That skill defines the fundamental RED-GREEN-REFACTOR cycle. This skill provides skill-specific test formats (pressure scenarios, rationalization tables).
Complete worked example: See examples/CLAUDE_MD_TESTING.md for a full test campaign testing CLAUDE.md documentation variants.
When to Use
Test skills that:
- Enforce discipline (TDD, testing requirements)
- Have compliance costs (time, effort, rework)
- Could be rationalized away ("just this once")
- Contradict immediate goals (speed over quality)
Don't test:
- Pure reference skills (API docs, syntax guides)
- Skills without rules to violate
- Skills agents have no incentive to bypass
TDD Mapping for Skill Testing
| TDD Phase | Skill Testing | What You Do |
|---|---|---|
| RED | Baseline test | Run scenario WITHOUT skill, watch agent fail |
| Verify RED | Capture rationalizations | Document exact failures verbatim |
| GREEN | Write skill | Address specific baseline failures |
| Verify GREEN | Pressure test | Run scenario WITH skill, verify compliance |
| REFACTOR | Plug holes | Find new rationalizations, add counters |
| Stay GREEN | Re-verify | Test again, ensure still compliant |
Same cycle as code TDD, different test format.
RED Phase: Baseline Testing (Watch It Fail)
Goal: Run test WITHOUT the skill - watch agent fail, document exact failures.
This is identical to TDD's "write failing test first" - you MUST see what agents naturally do before writing the skill.
What ships with it
1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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.
- 10d ago First seen · 388 lines · 57 tokens per session scan A b63b2231b235
testing-skills-with-subagents is a skill published in the GitHub repository movebrickschi/harness-engineering-mcp (2 stars, last pushed 3mo ago), licensed MIT. It adds 57 tokens to every session and 2,905 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. It is 98% identical to Testing Skills With Subagents, differing in 19 lines, and is treated as a copy.
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