# File lib/rspec/core/shared_example_group.rb, line 56
        def add_group(*args, &block)
          ensure_block_has_source_location(block, caller[1])

          if key? args.first
            key = args.shift
            warn_if_key_taken key, block
            RSpec.world.shared_example_groups[key] = block
          end

          unless args.empty?
            mod = Module.new
            (class << mod; self; end).send :define_method, :extended  do |host|
              host.class_eval(&block)
            end
            RSpec.configuration.extend mod, *args
          end
        end