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 agentmods add skills/matrixfounder/agentic-development/testing-best-practicesnpx skills add MatrixFounder/Agentic-development --skill testing-best-practicesgit clone --depth 1 https://github.com/MatrixFounder/Agentic-developmentWhat 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 | $0.00016 | $0.00326 |
| Opus 5 | $0.00008 | $0.00163 |
| Sonnet 5 | $0.00003 | $0.00065 |
| Haiku 4.5 | $0.00002 | $0.00033 |
Grade A, and why
testing-best-practices 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 2d 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.
What it actually says
Testing Best Practices
1. Hierarchy & Strategy
- E2E (End-to-End): Mandatory for every task.
- Stub Stage: Assert hardcoded values (verify structure).
- Impl Stage: Assert real logic (verify behavior).
- Unit: Cover edge cases, error handling, and specific algorithms.
- Regression: ALWAYS run the full test suite before submitting.
2. Critical Rules
- NO LLM MOCKING in Tests: Do not mock OpenAI/Anthropic calls in standard tests. Use recorded responses (VCR.py) or separate integration environments.
- Realism: Minimize mocks. Test real component capability where possible.
- Isolation: Tests must be independent. Database state should be reset between tests.
- Environment: Use the project's virtual environment (e.g.,
/opt/projects/.../venv).
3. Naming & Structure
- Clear Names:
test_shoud_return_error_when_invalid_input. - Organization: Mirror source structure (
src/auth->tests/auth). - Docstrings: specificy WHAT is being tested.
- Reference Examples:
- Python:
examples/pytest_structure.py - JavaScript:
examples/jest_structure.js
- Python:
4. Resources
- Templates: Use
assets/templates/test_boilerplate.pyto start new test files quickly.
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.
- 2d ago First seen · 32 lines · 16 tokens per session scan A a41cc3d4fc7b
testing-best-practices is a skill published in the GitHub repository MatrixFounder/Agentic-development (5 stars, last pushed 19d ago), licensed Apache-2.0. It adds 16 tokens to every session and 326 once invoked, about $0.0001 per session on Opus 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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