code: def test_train(self) -> None:
      class LogCallback(Callback):
          def __init__(self):
              super().__init__()
  
          def on_epoch_end(self, epoch, logs=None):
              self.logs = logs
  
      data = [("a b", "a"), ("a b c", "b")]
  
      summarizer = AttentionSummarizer(lstm_size=16, embedding_size=10)
      log_callback = LogCallback()
      trainer = Trainer(
          batch_size=2,
          steps_per_epoch=10,
          max_vocab_size_encoder=10,
          max_vocab_size_decoder=10,
          model_save_path=None,
          max_output_len=3,
      )
  
      trainer.train(
          summarizer, data, num_epochs=2, callbacks=[log_callback]
      )
  
      logs = log_callback.logs
      self.assertAlmostEqual(1.7135955810546875, logs["loss"], 6)
  
file_path: headliner/tests/test_trainer.py
imports: import tensorflow
  import logging
  import os
  import unittest
  import numpy
  from tensorflow.python.keras.callbacks import Callback
  from headliner.model import AttentionSummarizer
  from headliner.preprocessing.preprocessor import Preprocessor
  from headliner.trainer import Trainer
label_desc: Use image node_id 5 for calling the TestTrainer obj's underlying member method code with example usage: obj.test_train() without return types