class_docstr: This tests the trainer of DeepRepresentLinUCB.
class_docstr_tok: ["This","tests","the","trainer","of","DeepRepresentLinUCB","."]
code: def test_linucb_training_step(self):
      self.trainer.training_step(self.batch, 0)
      assert len(self.batch.action) == len(self.batch.reward)
      assert (
          len(self.batch.action)
          == self.batch.context_arm_features.shape[0]
      )
  
      loss = self.trainer.training_step(batch=self.batch, batch_idx=0)
      self.assertIsInstance(loss, torch.Tensor)
      self.assertEqual(loss.size(), ())
  
file_path: ReAgent/reagent/test/training/cb/test_deep_represent_linucb.py
imports: import unittest
  import torch
  from reagent.core.types import CBInput
  from reagent.gym.policies.policy import Policy
  from reagent.gym.policies.samplers.discrete_sampler import GreedyActionSampler
  from reagent.models.deep_represent_linucb import DeepRepresentLinearRegressionUCB
  from reagent.models.fully_connected_network import FullyConnectedNetwork
  from reagent.training.cb.deep_represent_linucb_trainer import DeepRepresentLinUCBTrainer
  from reagent.training.parameters import DeepRepresentLinUCBTrainerParameters
label_desc: Use image node_id 2 for calling the TestDeepRepresentLinUCB obj's underlying member method code with example usage: obj.test_linucb_training_step() without return types