code: def test_beam_lm_increase_src_len(self):
      beam = BeamSearchLM(
          self.BEAM_SZ,
          self.BATCH_SZ,
          0,
          1,
          2,
          3,
          1,
          self.N_BEST,
          GlobalScorerStub(),
          0,
          30,
          False,
          0,
          set(),
          False,
          0.0,
          False,
      )
      device_init = torch.zeros(1, 1)
      src_len = torch.randint(0, 30, (self.BATCH_SZ,))
      fn_map_state, _, _ = beam.initialize(device_init, src_len)
      expected_beam_scores = self.init_step(beam, 1)
      expected_beam_scores = self.first_step(
          beam, expected_beam_scores, 1
      )
      expected_beam_scores = self.second_step(
          beam, expected_beam_scores, 1
      )
      self.third_step(beam, expected_beam_scores, 1)
  
      n_steps = beam.alive_seq.shape[-1] - 1
      self.assertTrue(
          beam.src_len.equal(n_steps + fn_map_state(src_len, dim=0))
      )
  
imports: import unittest
  from onmt.translate.beam_search import BeamSearch, GNMTGlobalScorer
  from onmt.translate.beam_search import BeamSearchLM
  from copy import deepcopy
  import torch
label_desc: Use image node_id 2 for calling the TestBeamSearchLM obj's underlying member method code with example usage: obj.test_beam_lm_increase_src_len() without return types