docs: def cookbook_statement(cookbook_name, metadata=None):
          """Return a valid Ruby 'cookbook' statement for the Berksfile."""
          line = "cookbook '%s'" % cookbook_name
          if metadata:
              if not isinstance(metadata, dict):
                  raise TypeError("Berksfile dependency hash for %s "
                                  "should be a dict of options, not %s."
                                  % (cookbook_name, metadata))
              # not like the others...
              if 'constraint' in metadata:
                  line += ", '%s'" % metadata.pop('constraint')
              for opt, spec in metadata.items():
                  line += ", %s: '%s'" % (opt, spec)
          return line