old_contents: class MockStatement(object):
      """A class to imitate real INDRA Statements for calculating belief."""
      def __init__(self, mk_hash, evidence, supports=None, supported_by=None):
          if isinstance(evidence, list):
              self.evidence = evidence
          else:
              self.evidence = [evidence]
          self.__mk_hash = mk_hash
          if supports:
              self.supports = supports
          else:
              self.supports = []
          if supported_by:
              self.supported_by = supported_by
          else:
              self.supported_by = []
          self.belief = None
  
      def matches_key(self):
          return self.__mk_hash
  
  
  class MockEvidence(object):
      """A class to imitate real INDRA Evidence for calculating belief."""
      def __init__(self, source_api):
          self.source_api = source_api
  
          # Some annotations are used in indra.belief.tag_evidence_subtype.
          # TODO: optionally implement necessary annotations.
          self.annotations = {}
  
new_contents: class MockStatement(object):
      """A class to imitate real INDRA Statements for calculating belief."""
      def __init__(self, mk_hash, evidence, supports=None, supported_by=None):
          if isinstance(evidence, list):
              self.evidence = evidence
          else:
              self.evidence = [evidence]
          self.__mk_hash = mk_hash
          if supports:
              self.supports = supports
          else:
              self.supports = []
          if supported_by:
              self.supported_by = supported_by
          else:
              self.supported_by = []
          self.belief = None
  
      def matches_key(self):
          return self.__mk_hash
  
  
  class MockEvidence(object):
      """A class to imitate real INDRA Evidence for calculating belief."""
      def __init__(self, source_api):
          self.source_api = source_api
  
          # Some annotations are used in indra.belief.tag_evidence_subtype.
          # TODO: optionally implement necessary annotations.
          self.annotations = {}
  
  
  def populate_support(stmts, links):
      """Populate the supports supported_by lists of statements given links.
  
      Parameters
      ----------
      stmts : list[MockStatement/Statement]
          A list of objects with supports and supported_by attributes which are
          lists or equivalent.
      links : list[tuple]
          A list of pairs of hashes or matches_keys, where the first supports the
          second.
      """
      stmt_dict = {s.matches_key(): s for s in stmts}
      for supped_idx, supping_idx in links:
          stmt_dict[supping_idx].supports.append(stmt_dict[supped_idx])
          stmt_dict[supped_idx].supported_by.append(stmt_dict[supping_idx])
      return
  
subject: Add function to populate support from links.