class RSpec::Core::ExampleGroup

def self.describe(*args, &example_group_block)
  @_subclass_count ||= 0
  @_subclass_count += 1
  args << {} unless args.last.is_a?(Hash)
  args.last.update(:example_group_block => example_group_block)
  # TODO 2010-05-05: Because we don't know if const_set is thread-safe
  child = const_set(
    "Nested_#{@_subclass_count}",
    subclass(self, args, &example_group_block)
  )
  children << child
  child
end