@@ -44,6 +44,11 @@ module RSpec
         end
         self
       end
+
+      def clear
+        @values.clear
+        self
+      end
     end
   end
 end
module RSpec
  module Core
    # @private
    #
    # We use this to replace `::Set` so we can have the advantage of
    # constant time key lookups for unique arrays but without the
    # potential to pollute a developers environment with an extra
    # piece of the stdlib. This helps to prevent false positive
    # builds.
    #
    class Set
      include Enumerable

      def initialize(array=[])
        @values = {}
        merge(array)
      end

      def empty?
        @values.empty?
      end

      def <<(key)
        @values[key] = true
        self
      end

      def delete(key)
        @values.delete(key)
      end

      def each(&block)
        @values.keys.each(&block)
        self
      end

      def include?(key)
        @values.key?(key)
      end

      def merge(values)
        values.each do |key|
          @values[key] = true
        end
        self
      end
    end
  end
end

Mind adding a spec to `set_spec.rb` for this?