code: def test_translation_matrix(self):
      model = translation_matrix.BackMappingTranslationMatrix(
          self.source_doc_vec,
          self.target_doc_vec,
          self.train_docs[:5],
      )
      transmat = model.train(self.train_docs[:5])
      self.assertEqual(transmat.shape, (8, 8))
  
imports: from collections import namedtuple
  import unittest
  import logging
  import numpy
  import pytest
  from scipy.spatial.distance import cosine
  from gensim.models.doc2vec import Doc2Vec
  from gensim import utils
  from gensim.models import translation_matrix
  from gensim.models import KeyedVectors
  from gensim.test.utils import datapath, get_tmpfile
label_desc: Use image node_id 2 for calling the TestBackMappingTranslationMatrix obj's underlying member method code with example usage: obj.test_translation_matrix() without return types