Borrowing it
Nothing to install: this file belongs to DanielPodolsky/ownyourcode. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/DanielPodolsky/ownyourcode/main/.claude/skills/fundamentals/testing/SKILL.mdgit clone --depth 1 https://github.com/DanielPodolsky/ownyourcodeWrote 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/danielpodolsky/ownyourcode/testing)<a href="https://agentmods.dev/skills/danielpodolsky/ownyourcode/testing"><img src="https://agentmods.dev/badge/skills/danielpodolsky/ownyourcode/testing/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/danielpodolsky/ownyourcode/testing"><img src="https://agentmods.dev/badge/skills/danielpodolsky/ownyourcode/testing.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector pass
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 | $0.00067 | $0.01469 |
| Opus 5.5 | $0.00027 | $0.00588 |
| Sonnet 5.5 | $0.00013 | $0.00294 |
| Haiku 4.5 | $0.00007 | $0.00147 |
Grade A, and why
testing-fundamentals 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 — 219 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Testing Fundamentals Review
"If you can't test it, you don't understand it. Tests are proof of understanding."
When to Apply
Activate this skill when:
- Reviewing test files (*.test.ts, *.spec.ts, *.test.js)
- Junior asks about testing strategy
- Completing a feature without tests
- Discussing coverage or test quality
The Testing Pyramid
▲
╱ ╲ E2E (10%)
╱ ╲ Playwright - Full user flows
╱─────╲
╱ ╲ Integration (20%)
╱ ╲ Vitest + RTL - Component interactions
╱───────────╲
╱ ╲ Unit (70%)
╱ ╲ Vitest - Functions, utils, logic
─────────────────
- Unit Tests (70%): Fast, isolated, test one thing
- Integration Tests (20%): Components working together
- E2E Tests (10%): Critical user journeys only
Stack-Specific Framework Guide
| Stack | Unit/Integration | E2E |
|---|---|---|
| Vite + React | Vitest + React Testing Library | Playwright |
| Create React App | Jest + RTL | Playwright |
| Next.js | Vitest or Jest + RTL | Playwright |
| Node.js | Vitest (native ESM) | - |
| Python | pytest | - |
| Go | go test | - |
Why Vitest for Vite?
- 10-20x faster than Jest in watch mode
- Native ESM support
- Same config as Vite (vite.config.ts)
- Compatible with Jest API
What to Test (The 3 Questions)
- Happy Path: Does it work when everything goes right?
- Edge Cases: What happens with empty, null, max values?
- Error States: Does it fail gracefully?
Good Tests Check:
- Component renders without crashing
- User interactions work (click, type, submit)
- Error states display correctly
- Loading states appear and disappear
- Data flows correctly through the component
Bad Tests Check:
- Implementation details (internal state, method calls)
- Styling or CSS classes
- Third-party library internals
- Snapshot tests of large components (brittle)
Common Mistakes (Anti-Patterns)
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 · 219 lines · 67 tokens per session scan A ceb4ef6b6524
testing-fundamentals is a skill published in the GitHub repository DanielPodolsky/ownyourcode (292 stars, last pushed 4mo ago), licensed MIT. It adds 67 tokens to every session and 1,469 once invoked, about $0.0003 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 2026-08-30.
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