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 rileyhilliard/agentrc --skill writing-testsgit clone --depth 1 https://github.com/rileyhilliard/agentrcWrote 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/rileyhilliard/agentrc/writing-tests)<a href="https://agentmods.dev/skills/rileyhilliard/agentrc/writing-tests"><img src="https://agentmods.dev/badge/skills/rileyhilliard/agentrc/writing-tests/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/rileyhilliard/agentrc/writing-tests"><img src="https://agentmods.dev/badge/skills/rileyhilliard/agentrc/writing-tests.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 | $0.00033 | $0.00644 |
| Opus 5.5 | $0.00013 | $0.00258 |
| Sonnet 5.5 | $0.00007 | $0.00129 |
| Haiku 4.5 | $0.00003 | $0.00064 |
Grade A, and why
writing-tests 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 — 86 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Writing Tests
Core principle: Test user-observable behavior with real dependencies. Tests should survive refactoring.
"The more your tests resemble the way your software is used, the more confidence they can give you." — Kent C. Dodds
Why this matters: Tests exist to give you confidence. The Testing Trophy prioritizes integration tests because they test real behavior across real modules — giving maximum confidence per test written. Unit tests in isolation often just test mocks, not your actual system.
Testing Trophy Model
| Priority | Type | When |
|---|---|---|
| 1st | Integration | Default - multiple units with real dependencies |
| 2nd | E2E | Complete user workflows |
| 3rd | Unit | Pure functions only (no dependencies) |
Mocking Guidelines
Default: Don't mock. Use real dependencies.
Only mock:
- External HTTP/API calls
- Time/randomness
- Third-party services (payments, email)
Never mock:
- Internal modules
- Database queries (use test DB)
- Business logic
- Your own code calling your own code
Before mocking, ask: "What side effects does this have? Does my test need those?" If unsure, run with real implementation first, then add minimal mocking only where needed.
Test Type Decision
Complete user workflow? → E2E test
Pure function (no side effects)? → Unit test
Everything else → Integration test
Assertion Strategy
| Context | Assert On | Avoid |
|---|---|---|
| UI | Visible text, roles | CSS classes, internal state |
| API | Response body, status | Internal DB state |
| Library | Return values | Private methods |
Anti-Patterns
| Pattern | Fix |
|---|---|
| Testing mock calls | Test actual outcome |
| Test-only methods in production | Move to test utilities |
sleep(500) |
Use condition-based waiting |
| Asserting on internal state | Assert on observable output |
| Incomplete mocks | Mirror real API completely |
What ships with it
3 files 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 · 86 lines · 33 tokens per session scan A 2531b86474ad
writing-tests is a skill published in the GitHub repository rileyhilliard/agentrc (3 stars, last pushed 8mo ago), licensed MIT. It adds 33 tokens to every session and 644 once invoked, about $0.0001 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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