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 zacharygcook/agent-skills --skill expand-test-coveragegit clone --depth 1 https://github.com/zacharygcook/agent-skillsWrote 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/zacharygcook/agent-skills/expand-test-coverage)<a href="https://agentmods.dev/skills/zacharygcook/agent-skills/expand-test-coverage"><img src="https://agentmods.dev/badge/skills/zacharygcook/agent-skills/expand-test-coverage/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/zacharygcook/agent-skills/expand-test-coverage"><img src="https://agentmods.dev/badge/skills/zacharygcook/agent-skills/expand-test-coverage.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 | $0.00054 | $0.00467 |
| Opus 5.5 | $0.00022 | $0.00187 |
| Sonnet 5.5 | $0.00011 | $0.00093 |
| Haiku 4.5 | $0.00005 | $0.00047 |
Grade A, and why
expand-test-coverage 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 1mo 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.
How it starts
The opening of the file, as written. The whole thing — 52 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Expand Test Coverage
Add tests that increase confidence in reachable behavior, not just coverage percentages.
Establish Scope
- Prefer the user-named files, PR, branch, or commit.
- Otherwise inspect
git status,git diff, andgit diff --cached. - If the tree is clean, inspect the latest relevant commit.
- Read each changed file in full plus adjacent contracts and existing tests.
Before writing tests, identify the public behavior, critical invariants, error paths, state transitions, integration boundaries, and realistic edge cases. Follow the repository's existing framework, fixtures, naming, and command conventions.
Select Valuable Cases
Prioritize:
- critical happy paths and business invariants;
- realistic validation, authorization, not-found, and provider failures;
- boundary values and malformed external data;
- important state transitions and retry/idempotency behavior;
- regression cases for confirmed bugs;
- integration behavior where mocks would hide the risk.
Avoid tests that only restate implementation details, assert framework behavior, exercise unreachable branches, or preserve dead code. If a branch has no production path, simplify or delete it instead of inventing a test.
Iterate
- Write a small coherent batch.
- Run the narrowest relevant test command immediately.
- Diagnose every failure before editing.
- Fix production code when the test reveals a real defect; fix the test when its premise or setup is wrong.
- Repeat until the planned behavior passes.
- Run the broader affected suite, then the full suite when proportionate and practical.
Never weaken an assertion, over-mock a boundary, or change expected behavior merely to turn the suite green. When intent is ambiguous, use docs, call sites, and existing tests as evidence and report the uncertainty.
Handoff
Report:
- behavior covered and tests added;
- implementation bugs found and fixed;
- focused and full commands run with results;
- anything not run and why;
- remaining meaningful gaps, not raw uncovered-line counts.
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.
- 1mo ago First seen · 52 lines · 54 tokens per session scan A 314b81cb4b22
expand-test-coverage is a skill published in the GitHub repository zacharygcook/agent-skills (2 stars, last pushed 3mo ago), licensed MIT. It adds 54 tokens to every session and 467 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 2026-08-31.
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