example_spec.rb

subject { App.new }

App::PURPOSES.each do |p,_|
  context do
    before { subject.purpose = p }
    its(:purpose){ should == p }
  end
end

App::PLATFORMS.each do |p,_|
  context do
    before { subject.platform = p }
    its(:platform){ should == p }
  end
end

original_spec.rb

let(:app) { App.new }

%w(purpose platform).each do |meth|
  describe "#{meth}=" do
    App.const_get(meth.pluralize.upcase).each do |attribute,_|
      it "accepts #{attribute} as a valid value" do
        app.send "#{meth}=", attribute
        app.send(meth).should == attribute
      end
    end
  end
end

nice one burns. i've changed mine.

• i like the underscore block var.
• yours is very clean but i prefer not to set platform in the before block as its the functionality being tested.
• what's yours look like run with the documentation formatter?
• the way this project changes another attribute similar to platform and purpose will be added. all i have to do is thype one word to get the extra test