code: def get_input_dim(self) -> int:
      return self.input_dim
  
imports: import torch
  import numpy
  import pytest
  from allennlp.common.testing import AllenNlpTestCase
  from allennlp.modules.seq2seq_encoders import ComposeEncoder, FeedForwardEncoder, Seq2SeqEncoder
  from allennlp.modules import FeedForward
label_desc: Use image node_id 3 for calling the MockSeq2SeqEncoder obj's underlying member method code with example usage: obj.get_input_dim() and returns: self