rspec-service-testing

RSpec Service Testing

Use this skill when writing tests for service classes under spec/services/.

Core principle: Test the public contract (.call, .find, .search), not internal implementation. Use instance_double for isolation, create for integration.

Workflow: Write → Run → Verify → Fix

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

DO NOT implement the service before step 1 is written and failing for the right reason.

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)

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) }

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') }

See PATTERNS.md for the full pattern and factory placement guidance.

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
• Logger expectations for error logging

Common Mistakes

Mistake	Correct approach
No error scenario tests	Happy path only = false confidence — always test failures
let! everywhere	Use let (lazy) unless the value is needed unconditionally for setup
Huge factory setup	Keep factories minimal — only attributes required for the test
Spec breaks when implementation changes but behavior is unchanged	Tests that break on refactoring are testing internals, not contracts

Integration

Skill	When to chain
rspec-best-practices	For general RSpec style and TDD discipline
ruby-service-objects	For the service conventions being tested
ruby-api-client-integration	For API client layer testing patterns
rails-engine-testing	When testing engine-specific services

Assets

• assets/spec_examples.md
• assets/testing_checklist.md