code: def test_train_one_step(self):
      ctable = create_ctable()
      batch = ctable.get_batch(128)
  
      state = create_train_state(ctable)
      key = random.key(0)
      _, train_metrics = train.train_step(
          state, batch, key, ctable.eos_id
      )
  
      self.assertLessEqual(train_metrics["loss"], 5)
      self.assertGreaterEqual(train_metrics["accuracy"], 0)
  
file_path: flax/examples/seq2seq/train_test.py
imports: import functools
  from absl.testing import absltest
  from flax.training import train_state
  import jax
  from jax import random
  import numpy
  import optax
  import input_pipeline
  import train
  import models
label_desc: Use image node_id 4 for calling the TrainTest obj's underlying member method code with example usage: obj.test_train_one_step() without return types