code: def _check_for_degenerate_interesting_groups(items):
      
      igkey = ("algorithm", "bcbiornaseq", "interesting_groups")
      interesting_groups = tz.get_in(igkey, items[0], [])
      if isinstance(interesting_groups, str):
          interesting_groups = [interesting_groups]
      for group in interesting_groups:
          values = [tz.get_in(("metadata", group), x, None) for x in items]
          if all(x is None for x in values):
              raise ValueError("group %s is labelled as an interesting group, "
                               "but does not appear in the metadata." % group)
          if len(list(tz.unique(values))) == 1:
              raise ValueError("group %s is marked as an interesting group, "
                               "but all samples have the same value." % group)
docs: Make sure interesting_groups specify existing metadata and that
      the interesting_group is not all of the same for all of the samples