testimony_service_spec.rb

require 'rails_helper'

RSpec.describe TestimonyService, type: :service do
  subject { described_class.new }
  let!(:user) { create(:user, status: 'active') }
  let!(:course) { create :course }

  context '.create' do
    context 'when valid' do
       let(:attributes) { attributes_for(:testimony, course_id: course.id) }

       it 'create a new' do
         expect do
           subject.create(attributes)
         end.to change(Testimony, :count).by(1)
       end

       it 'correct attributes' do
         testimony = subject.create(attributes)
         expect(testimony.body).to eql(attributes[:body])
         expect(testimony.score).to eql(attributes[:score])
         expect(testimony.email).to eql(attributes[:email])
         expect(testimony.full_name).to eql(attributes[:full_name])
         expect(testimony.course).to eql(course)
         expect(testimony).to be_queue
       end

       it 'send a e-mail' do
         expect do
           subject.create(attributes)
         end.to change(ActionMailer::Base.deliveries, :count).by(1)
       end
     end

     context 'when invalid' do
       let(:attributes) { attributes_for(:invalid_testimony) }

       it 'not create' do
         expect do
           subject.create(attributes)
         end.to change(Testimony, :count).by(0)
       end

       it 'not send a e-mail' do
         expect do
           subject.create(attributes)
         end.to change(ActionMailer::Base.deliveries, :count).by(0)
       end
     end
   end

   context 'approve!' do
     let(:testimony) { create(:testimony, status: 'approved') }

     before { subject.approve!(testimony) }
     it { expect(testimony).to be_approved }

     it 'send a e-mail' do
       expect do
         subject.approve!(testimony)
       end.to change(ActionMailer::Base.deliveries, :count).by(1)
     end
   end

   context 'disapprove!' do
     let(:testimony) { create(:testimony, status: 'queue') }

     before { subject.disapprove!(testimony) }
     it { expect(testimony).to be_disapproved }

     it 'send a e-mail' do
       expect do
         subject.approve!(testimony)
       end.to change(ActionMailer::Base.deliveries, :count).by(1)
     end
   end

1. https://robots.thoughtbot.com/mystery-guest
2. https://robots.thoughtbot.com/four-phase-test