anchor.diff:    {ok, Doc4} = barrel_db:get(<<"testdb">>, DocId, [{history, true}]),
     Revisions = barrel_doc:parse_revisions(Doc4),
     Revisions == [RevId2, RevId].
  +
  +put_rev(_Config) ->
  +  Doc = #{<<"v">> => 1},
  +  {ok, DocId, RevId} =  barrel_db:post(<<"testdb">>, Doc, []),
  +  {ok, Doc2} = barrel_db:get(<<"testdb">>, DocId, []),
  +  Doc3 = Doc2#{ v => 2},
  +  {ok, DocId, RevId2} = barrel_db:put(<<"testdb">>, DocId, Doc3, []),
  +
  +  Doc4_0 = Doc2#{ v => 3 },
  +  {Pos, _} = barrel_doc:parse_revision(RevId),
  +  NewRev = barrel_doc:revid(Pos +1, RevId, Doc4_0),
  +  Doc4 = Doc4_0#{<<"_rev">> => NewRev},
  +  History = [NewRev, RevId],
  + 
  +  {ok, DocId, RevId3} = barrel_db:put_rev(<<"testdb">>, DocId, Doc4, History, []),
  +  {ok, Doc5} = barrel_db:get(<<"testdb">>, DocId, [{history, true}]),
  +  Revisions = barrel_doc:parse_revisions(Doc5),
  +  Revisions == [RevId2, RevId].
  +
   
   fold_by_id(_Config) ->
     Doc = #{ <<"_id">> => <<"a">>, <<"v">> => 1},
  
positive.code:     get_revisions,
      fold_by_id,
      change_since,
      revdiff
    ].
  
  init_per_suite(Config) ->
  
negative.code:   fold_by_id/1,
    change_since/1,
    revdiff/1,
    get_revisions/1,
    put_rev/1
  ]).
  
  all() ->
  