Test Service

Quick Reference

Aspect	Rule
File location	spec/services/module_name/service_spec.rb
Subject	subject(:service_call) { described_class.call(params) }
Unit isolation	instance_double for collaborators
Integration	create for DB-backed tests
Multi-assertion	aggregate_failures
State verification	change matchers
Time-dependent	travel_to
API responses	FactoryBot hash factories (class: Hash)

HARD-GATE

DO NOT implement the service before step 1 is written and failing for the right reason.
1. WRITE:   Write the spec (happy path + error cases + edge cases)
2. RUN:     bundle exec rspec spec/services/your_service_spec.rb
3. VERIFY:  Confirm failures are for the right reason (not a typo or missing factory)
4. FIX:     Implement or fix until the spec passes
5. SUITE:   bundle exec rspec spec/services/ — verify no regressions

Core Process

Spec Template

# frozen_string_literal: true

require 'spec_helper'

RSpec.describe ModuleName::MainService do
  describe '.call' do
    subject(:service_call) { described_class.call(params) }

    let(:shelter) { create(:shelter, :with_animals) }
    let(:params) do
      { shelter: { shelter_id: shelter.id }, items: %w[TAG001 TAG002] }
    end

    context 'when input is valid' do
      before { create(:animal, tag_number: 'TAG001', shelter:) }

      it 'returns success' do
        expect(service_call[:success]).to be true
      end
    end

    context 'when shelter is not found' do
      let(:params) { super().merge(shelter: { shelter_id: 999_999 }) }

      it 'returns error response' do
        expect(service_call[:success]).to be false
      end
    end

    context 'when input is blank' do
      let(:params) { { shelter: { shelter_id: nil }, items: [] } }

      it 'returns error response with meaningful message' do
        aggregate_failures do
          expect(service_call[:success]).to be false
          expect(service_call[:errors]).not_to be_empty
        end
      end
    end
  end
end

Use instance_double for unit isolation:

let(:client) { instance_double(Api::Client) }
before { allow(client).to receive(:execute_query).and_return(api_response) }

CRITICAL — Collaborators MUST be stubbed via instance_double. Three patterns:

• Inject dependency: pass the double in params directly.
• Stub .new: allow(CarrierApi::Client).to receive(:new).and_return(client) when the service instantiates internally.
• Avoid class-level stubs: do not use allow(CarrierApi::Client).to receive(:notify) — always double the instance.

Use create for integration tests:

let(:source_shelter) { create(:shelter, :with_animals) }

FactoryBot Hash Factories for API Responses

When testing API clients, use class: Hash with initialize_with to build hash-shaped response fixtures. A minimal example:

FactoryBot.define do
  factory :api_animal_response, class: Hash do
    tag_number { 'TAG001' }
    status     { 'active' }

    initialize_with { attributes.stringify_keys }
  end
end

# In the spec:
let(:api_response) { build(:api_animal_response, tag_number: 'TAG002') }

New Test File Checklist

• subject defined for the main action
• instance_double for unit / create for integration
• Happy path for each public method
• Error and edge cases (blank input, invalid refs, failures)
• Partial success scenarios where relevant
• shared_examples for repeated patterns
• aggregate_failures for multi-assertion tests
• change matchers for state verification

Common Mistakes

Mistake	Correct approach
No error scenario tests	Always test failures alongside the happy path
let! everywhere	Use let (lazy) unless the value is unconditionally required for setup
Huge factory setup	Keep factories minimal — only attributes the test requires
Spec breaks on refactor with unchanged behavior	Tests that break on refactoring are testing internals, not contracts

Extended Resources (Progressive Disclosure)

Load these files only when their specific content is needed:

• PATTERNS.md — Use when you need the full pattern catalog and factory placement guidance
• assets/spec_examples.md — Use when you need additional worked examples beyond the spec template above
• assets/testing_checklist.md — Use when reviewing a completed service spec for completeness

Output Style

When completing a service test, output MUST include:

# Service Spec — [ServiceName]

## Spec File
- Path: spec/services/<module>/<service>_spec.rb
- Subject: `described_class.call(params)`

## Coverage
- Happy path: ✓ (<n> examples)
- Error cases: ✓ (<n> examples — list error classes/conditions)
- Edge cases: ✓ (<n> examples — blank input, boundary values)
- Isolation: instance_double for <collaborator list>

## TDD Gate
- RED: <failure message confirming missing behavior>
- GREEN: <all examples pass>
- Suite: <full spec/services/ suite status>

Integration

Skill	When to chain
write-tests	For general RSpec style and TDD discipline
create-service-object	For the service conventions being tested
integrate-api-client	For API client layer testing patterns
test-engine	When testing engine-specific services