anchor.diff:        selector['name'] = name;
         MongoInsertMessage insertMessage = new MongoInsertMessage(
             '$databaseName.${DbCommand.SYSTEM_INDEX_COLLECTION}', [selector]);
  -      executeMessage(insertMessage, _writeConcern);
  +      await executeMessage(insertMessage, _writeConcern);
         return getLastError();
       });
     }
  
positive.code:       bool sparse,
        bool background,
        bool dropDups,
        String name}) {
      return new Future.sync(() {
        keys = _setKeys(key, keys);
        return collection(collectionName).getIndexes().then((indexInfos) {
          if (name == null) {
            name = _createIndexName(keys);
          }
          if (indexInfos.any((info) => info['name'] == name)) {
            return new Future.value({'ok': 1.0, 'result': 'index preexists'});
          }
          return createIndex(collectionName,
              keys: keys,
              unique: unique,
              sparse: sparse,
              background: background,
              dropDups: dropDups,
              name: name);
        });
      });
    }
  
    Future _getAcknowledgement({WriteConcern writeConcern}) {
  
negative.code:       bool background,
        bool dropDups,
        String name}) {
      return new Future.sync(() async {
        var selector = {};
        selector['ns'] = '$databaseName.$collectionName';
        keys = _setKeys(key, keys);
  