leveraging Subject in RSpec - 4

address_spec.rb

describe Address do
  describe "#validations" do

    #The line below can be omited if we were to not use Factory and use Address.new and innermost 'describe' block is Address implicitly.
    subject { Factory.build :address }

    %w(:city :state :country).each do |attr|
      it "must have a #{attr}" do 
        subject.send("#{attr}=",nil)
        should_not be_valid    #should is called on a subject by default. Thus this line uses implicit subject :address marked above
        subject.errors.on(attr).should_not be_nil
      end
    end
    
  end
end