Agent skill

rails-testing-patterns

Analyzes Rails test suites and recommends testing best practices for RSpec and Minitest. Use when writing new tests, reviewing test coverage, fixing flaky tests, improving test performance, choosing between test types (unit, integration, system, request), or setting up factories and fixtures. NOT for production monitoring, deployment verification, or load/stress testing infrastructure.

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npx add-skill https://github.com/ag0os/rails-dev-plugin/tree/main/skills/rails-testing-patterns

SKILL.md

Rails Testing Patterns

Use standard RSpec and Minitest conventions for syntax, assertions, matchers, and Capybara DSL. This skill focuses on opinionated choices — what to test, which framework to use, and how to structure test data.

See patterns.md for decision guidance and non-obvious patterns.

Test Type Decision Matrix

Test Type When to Write Speed ROI Notes
Unit (Model) Business logic, validations, scopes, custom methods Fast Highest ROI — write these first in service-oriented stacks
Request API endpoints, auth flows, param handling Medium Highest ROI for api-first stacks; prefer over controller specs in RSpec
Integration Multi-step workflows spanning controllers Medium Omakase priority — tests the full stack as Rails intends
System Critical user journeys only (sign-up, checkout, onboarding) Slow Limit to 10-20 per app; never test CRUD forms with system tests
Mailer Non-trivial email content, conditional delivery Fast Skip if mailer is just a default scaffold
Job Idempotency, retry behavior, side effects Fast Always test jobs that touch external services

Profile-Aware Testing

Detect the project's profile before recommending a testing approach.

Decision Omakase Service-Oriented API-First
Framework Minitest RSpec RSpec
Test data Fixtures FactoryBot FactoryBot
Directory test/ spec/ spec/
First tests to write Integration/controller tests Unit tests + request specs Request specs
System tests Yes, for key flows Sparingly No — use request specs

Anti-Patterns

Anti-Pattern Do Instead Why
Testing Rails internals (validates_presence_of works?) Test your domain logic only Rails is already tested
sleep in system tests Rely on Capybara's built-in waiting (have_content, assert_text) Sleep is flaky and slow
Shared mutable state between tests Fresh state per test via let/setup Test ordering bugs are the hardest to debug
Testing private methods directly Test through the public interface Couples tests to implementation
Huge factory/fixture with every field Minimal defaults + traits/overrides Reduces test fragility and speeds diagnosis
System tests for CRUD forms Request/integration tests 10x faster, same coverage for form submissions
Mocking the object under test Mock collaborators, not the subject Tests nothing useful

Test Data Strategy

Omakase — fixtures first:

  • Fixtures are loaded once per test run (fast) and double as development seed data
  • Use realistic, named fixtures: jane:, admin: — never user_1:, user_2:
  • Use inline Model.new(...) only for one-off edge cases not worth a fixture
  • Fixture files are the canonical source of test data — keep them curated

Service-oriented / API-first — factories first:

  • Minimal factory defaults — only required fields, everything else via traits
  • Use build (not create) whenever persistence isn't needed — dramatically faster
  • Use sequence for uniqueness constraints (emails, slugs)
  • Avoid deeply nested create chains — if a test needs 4+ create calls, consider fixtures for that scenario
  • Reserve fixtures for truly static reference data (countries, currencies)

Edge Cases to Always Test

  • Nil / blank / empty inputs
  • Boundary values (0, -1, MAX)
  • Unauthorized and forbidden access
  • Invalid parameter combinations
  • Concurrent modifications (optimistic locking, uniqueness races)

Output Format

When reporting on test quality, use:

## Test Analysis: [spec_or_test_file]

**Coverage Gaps:**
- [model/action] missing test for [scenario]

**Issues:**
- [severity] description

**Recommendations:**
1. actionable recommendation

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