Plain Old Decorators

greeter.rb

class Greeter
  def greet(user)
    user_name_decorator = UserNameDecorator.new(user)
    
    @greeting = user_name_decorator.dear_mr_user
    @greeting << "\n"
    @greeting << "Bla bla bla"
    ...
    @greeting << "\n"
  end
end

user_name_decorator.rb

# There can be number of user decorators for different purposes
#
class UserNameDecorator
  attr_reader :user
  
  def initialize(user)
    @user = user
    
    raise "No user given" unless user # Blowup earlier in case there is no user given
  end
  
  def dear_mr_user
    "Dear mr. #{full_name}" 
  end

  def full_name
    "#{user.first_name} #{user.last_name}" 
  end
end

user_name_decorator_spec.rb

# Testing like a regular object
#
describe UserNameDecorator do
  subject { described_class.new(user) }
  
  describe "#dear_mr_user" do
    let(:user) { create(:user, first_name: "Alex", last_name: "Pushkin") }
    
    it "greets user" do
      expect(subject.dear_mr_user).to eq("Dear mr. Alex Pushkin")
    end
  end
  
  ...
end