services.rb

class CollectionProcessor
  attr_reader :collection, :service

  def initialize(collection: collection, service: service)
    @collection = collection
    @service = service
  end

  def call
    collection.map do |item|
      service.new(item: item).call
    end
  end
end

class BitOfLoveGiver
  attr_reader :item

  def initialize(item: item)
    @item = item
  end

  def call
    give_a_bit_of_love(item)
  end

  private

  def give_a_bit_of_love
    { **item, ♥: true }
  end
end

users = [
  { name: 'Ivan' },
  { name: 'Joe' },
  { name: 'Jose' }
]

CollectionProcessor.new(
  collection: users,
  service: BitOfLoveGiver
).call


#### Spec ####

describe CollectionProcessor do
  let(:collection) { [
    { name: 'Ivan' },
    { name: 'Joe' },
    { name: 'Jose' }
  ] }

  subject { described_class.new(collection: collection, service: service) }

  context 'success' do
    let(:service) do
      double(new: -> { { ♥: true } })
    end
    
    it 'calls service' do
      result = subject.call
      expect(result.first).to have_key(:♥)
    end
  end

  context 'fail' do
    let(:service) do
      double(new: -> { raise 'Not today!' })
    end

    it 'raises error' do
      expect { subject.call }.to raise_error
    end
  end
end