class Rspec::Core::ExampleGroup

def self.describe(*args, &example_group_block)
  raise(ArgumentError, "No arguments given.  You must a least supply a type or description") if args.empty? 
  raise(ArgumentError, "You must supply a block when calling describe") if example_group_block.nil?
  @_subclass_count ||= 0
  @_subclass_count += 1
  const_set(
    "Nested_#{@_subclass_count}",
    _build(Class.new(self), caller, args, &example_group_block)
  )
end