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 rules/levifig/rails-instructions/testinggit clone --depth 1 https://github.com/levifig/rails-instructionsWhat 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 | $0.00000 | $0.01033 |
| Opus 5 | $0.00000 | $0.00517 |
| Sonnet 5 | $0.00000 | $0.00207 |
| Haiku 4.5 | $0.00000 | $0.00103 |
Grade A, and why
testing 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 yesterday.
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 — 185 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Rails Testing Guide
Core Philosophy
- Test-Driven Development (TDD) as default practice
- Use Minitest and fixtures, not RSpec or factories
- Test behavior, not implementation details
- Keep tests fast, focused, and reliable
- Write tests that serve as documentation
Testing Principles
- Write tests first, then implementation
- One assertion per test when possible
- Test the happy path and edge cases
- Keep test data realistic and minimal
- Make tests independent and repeatable
Test Organization
- Mirror app structure in test directory
- Group related tests in the same file
- Use descriptive test names
- Keep test files focused and manageable
- Organize tests by feature or behavior
Fixtures Best Practices
- Use fixtures for test data, not factories
- Keep fixtures simple and realistic
- Reference fixtures by meaningful names
- Share fixtures across related tests
- Update fixtures when models change
Model Testing
- Test all validations thoroughly
- Verify associations work correctly
- Test scopes with various data sets
- Check business logic and calculations
- Ensure callbacks behave properly
Controller Testing
- Focus on HTTP concerns only
- Test authentication and authorization
- Verify response formats and status codes
- Check parameter filtering
- Test error handling scenarios
System Testing
- Test complete user workflows
- Use Capybara for browser automation
- Test JavaScript interactions
- Verify Turbo Frame updates
- Check responsive behavior
Service Object Testing
- Test services in complete isolation
- Mock external dependencies
- Verify success and failure paths
- Test edge cases and error conditions
- Ensure proper transaction handling
Integration Testing
- Test API endpoints thoroughly
- Verify request/response cycles
- Test authentication flows
- Check cross-controller workflows
- Validate data consistency
Test Data Management
- Keep test data minimal and focused
- Use fixtures for common scenarios
- Create data in tests for specific cases
- Clean up after tests when needed
- Avoid test data dependencies
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.
- yesterday First seen · 185 lines · 0 tokens per session scan A c6ff38be3cb0
testing is a cursor rule published in the GitHub repository levifig/rails-instructions (54 stars, last pushed 1y ago), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 1,033 tokens. 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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Below is an example test, you'll notice the following.