parent_subject_example_spec.rb

require 'rspec'
require 'active_support/core_ext/array'

describe do
  def parent_subject
    self.class.ancestors[1].instance_variable_get('@explicit_subject_block').call
  end

  subject { [:one, :two, :three] }

  its(:first)  { should == :one }
  its(:second) { should == :two }

  describe 'its third' do
    subject { parent_subject[2] }
    it{ should == :three }
  end
end