class RSpec::Core::Metadata

def ensure_valid_keys(user_metadata)
  RESERVED_KEYS.each do |key|
    if user_metadata.has_key?(key)
      raise <<-EOM
      #{"*"*50}
} is not allowed
reserves some hash keys for its own internal use,
ing :#{key}, which is used on:
      #{caller(0)[4]}.
re all of RSpec's reserved hash keys:
      #{RESERVED_KEYS.join("\n  ")}
      #{"*"*50}
      EOM
    end
  end
end