From http://johnewart.net/posts/2014/09/ruby_interfaces/

interface_spec.rb

describe FunctionalInterface do
	before :all do
	  @implementations =
	    ObjectSpace.each_object(Class)
	      .select { |klass| klass < FunctionalInterface }
	end

	it "should enforce that the interface is implemented" do
	  @implementations.each do |klass|
	    entity = klass.new
	    expect { entity.do_thing }.to not_raise
	  end
	end
end