docstr: Add mask token at the last position according to the lengths of item_seq
docstr_tok: ["Add","mask","token","at","the","last","position","according","to","the","lengths","of","item_seq"]
code: def reconstruct_test_data(self, item_seq, item_seq_len):
      """
      Add mask token at the last position according to the lengths of item_seq
      """
      padding = torch.zeros(
          item_seq.size(0), dtype=torch.long, device=item_seq.device
      )  # [B]
      item_seq = torch.cat(
          (item_seq, padding.unsqueeze(-1)), dim=-1
      )  # [B max_len+1]
      for batch_id, last_position in enumerate(item_seq_len):
          item_seq[batch_id][last_position] = self.mask_token
      item_seq = item_seq[:, 1:]
      return item_seq
  
file_path: RecBole/recbole/model/sequential_recommender/bert4rec.py
imports: import random
  import torch
  from torch import nn
  from recbole.model.abstract_recommender import SequentialRecommender
  from recbole.model.layers import TransformerEncoder
label_desc: Use image node_id 3 for calling the BERT4Rec obj's underlying member method code with example usage: obj.reconstruct_test_data(item_seq, item_seq_len) and returns: item_seq