code: def test_loss_fn(self):
      model = AutoModelForSeq2SeqLM.from_pretrained(BART_TINY)
      input_ids, mask = (
          model.dummy_inputs["input_ids"],
          model.dummy_inputs["attention_mask"],
      )
      target_ids = torch.tensor(
          [[0, 4, 8, 2], [0, 8, 2, 1]],
          dtype=torch.long,
          device=model.device,
      )
      decoder_input_ids = target_ids[
          :, :-1
      ].contiguous()  # Why this line?
      lm_labels = target_ids[:, 1:].clone()  # why clone?
      model_computed_loss = model(
          input_ids,
          attention_mask=mask,
          decoder_input_ids=decoder_input_ids,
          labels=lm_labels,
          use_cache=False,
      ).loss
  
      logits = model(
          input_ids,
          attention_mask=mask,
          decoder_input_ids=decoder_input_ids,
          use_cache=False,
      ).logits
  
      lprobs = nn.functional.log_softmax(logits, dim=-1)
      smoothed_loss, nll_loss = label_smoothed_nll_loss(
          lprobs, lm_labels, 0.1, ignore_index=model.config.pad_token_id
      )
      with self.assertRaises(AssertionError):
          # TODO: understand why this breaks
          self.assertEqual(nll_loss, model_computed_loss)
  
imports: import argparse
  import logging
  import os
  import sys
  import tempfile
  from pathlib import Path
  import lightning_base
  import pytest
  import pytorch_lightning
  import torch
  from convert_pl_checkpoint_to_hf import convert_pl_to_hf
  from distillation import distill_main
  from finetune import SummarizationModule, main
  from huggingface_hub import list_models
  from parameterized import parameterized
  from run_eval import generate_summaries_or_translations
  from torch import nn
  from transformers import AutoConfig, AutoModelForSeq2SeqLM
  from transformers.testing_utils import CaptureStderr, CaptureStdout, TestCasePlus, require_torch_gpu, slow
  from utils import label_smoothed_nll_loss, lmap, load_json
label_desc: Use image node_id 5 for calling the TestSummarizationDistiller obj's underlying member method code with example usage: obj.test_loss_fn() without return types