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igmarin/rails-agent-skills

Curated library of 28 public AI agent skills for Ruby on Rails development. Organized by category: testing, code-quality, engines, infrastructure, api, and context. Covers code review, architecture, security, testing (RSpec), engines, Hotwire, and TDD automation. Shared Ruby skills (YARD docs, DDD, service objects) have moved to ruby-core-skills. Repository agents remain documented in GitHub but are intentionally excluded from the Tessl tile.

93

1.78x
Quality

95%

Does it follow best practices?

Impact

93%

1.78x

Average score across 28 eval scenarios

SecuritybySnyk

Passed

No known issues

Overview
Quality
Evals
Security
Files

SKILL.mdskills/engines/test-engine/

name:
test-engine
license:
MIT
description:
Use when creating or improving RSpec test coverage for Rails engines. Covers dummy app setup, request, routing, generator, and configuration specs for proving engine behavior within a host application.
metadata:
{"version":"1.0.0","user-invocable":"true"}

Test Engine

Use this skill when the task is to create or improve test coverage for a Rails engine.

Quick Reference

Spec TypeEngine-Specific Nuance
RequestTest via engine's named route helper (e.g., my_engine.root_path) to verify correct mounting in the host
RoutingAssert routes are scoped to the engine namespace; test with and without a custom mount point
GeneratorAssert idempotency (safe to run twice); verify files are copied to expected host app paths
ConfigOverride default in around block; assert the engine uses the host-provided value, not its own default
Reload-safetyCover to_prepare hooks and decorator re-application across code reloads in development mode

HARD-GATE

EVERY engine MUST have a dummy app for testing.
If it doesn't exist, generate it:
cd my_engine && bundle exec rails plugin new . --dummy-path=spec/dummy --skip-git

Validate the dummy app boots before proceeding:
cd spec/dummy && bundle exec rails runner "puts 'Boot OK'"

If this fails, check the engine's `engine.rb` initializer order and ensure the engine is correctly mounted in `spec/dummy/config/routes.rb` before writing any specs.

Core Process

  1. Identify the engine type and public behaviors.
  2. Decide which behaviors need unit tests versus dummy-app integration tests.
  3. Add the smallest integration test that proves mounting and boot work. Verify it passes before continuing — if it fails, check engine.rb initializer order and mount configuration rather than adding more specs on top of a broken foundation.
  4. Add request, routing, configuration, and generator coverage as needed.
  5. Add regression tests for coupling or reload bugs before refactoring.
  6. Verify: dummy app exercises real host integration; routes tested through engine namespace; configurable seams covered with at least one non-default case; generators safe to run twice.

Minimal request spec to prove the engine mounts:

# spec/requests/my_engine/root_spec.rb
require 'rails_helper'

RSpec.describe 'MyEngine mount', type: :request do
  it 'returns ok for the engine root' do
    get my_engine.root_path
    expect(response).to have_http_status(:ok)
  end
end

Configuration spec (engine respects host config):

# spec/my_engine/configuration_spec.rb
RSpec.describe MyEngine::Configuration do
  around do |example|
    original = MyEngine.config.widget_count
    MyEngine.config.widget_count = 3
    example.run
    MyEngine.config.widget_count = original
  end

  it 'uses configured value' do
    expect(MyEngine.config.widget_count).to eq(3)
  end
end

Extended Resources

Pitfalls

PitfallWhat to do
Skipping reload-safety testsAdd regression coverage for decorators and patches in development
Tests pass only with specific Rails versionRun a version matrix; pin nothing unless required
Request specs use stubs instead of real wiringMount the engine in dummy and call through it
Install generators without file assertionsAssert copied files and idempotency in generator specs

For generator and reload-safety spec examples, see assets/examples.md.

Integration

SkillWhen to chain
create-engineWhen structuring the engine for testability or adding configuration seams
review-engineWhen validating test coverage adequacy or identifying gaps
write-testsWhen improving spec structure, matchers, or shared examples

skills

engines

test-engine

EXAMPLES.md

SKILL.md

README.md

tile.json