anchor.diff:      get_revisions,
       fold_by_id,
       change_since,
  -    revdiff
  +    revdiff,
  +    put_rev
     ].
   
   init_per_suite(Config) ->
  
positive.code:   {ok, Doc4} = barrel_db:get(<<"testdb">>, DocId, [{history, true}]),
    Revisions = barrel_doc:parse_revisions(Doc4),
    Revisions == [RevId2, RevId].
  
  fold_by_id(_Config) ->
    Doc = #{ <<"_id">> => <<"a">>, <<"v">> => 1},
  
negative.code:   fold_by_id/1,
    change_since/1,
    revdiff/1,
    get_revisions/1,
    put_rev/1
  ]).
  
  all() ->
  