subject, specify, let

test_spec.rb

#http://stackoverflow.com/questions/9778657/why-does-this-simple-rspec-string-equality-spec-fail
describe First do
  specify { First.new.to_s.should == "Hello World" }
end

describe First do
  describe "#to_s" do
    subject { First.new.to_s }
    it { should == "Hello World" }
  end
end

describe First do
  describe "#to_s" do
    let(:result) { First.new.to_s }
    specify { result.should == "Hello World" }
  end
end