code: def test_linucb_training_step(self):
      self.trainer.training_step(self.batch, 0)
  
file_path: ReAgent/reagent/test/training/cb/test_disjoint_linucb.py
imports: import copy
  import unittest
  import numpy
  import numpy.testing
  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.disjoint_linucb_predictor import DisjointLinearRegressionUCB
  from reagent.training.cb.disjoint_linucb_trainer import DisjointLinUCBTrainer
  from reagent.training.parameters import DisjointLinUCBTrainerParameters
label_desc: Use image node_id 2 for calling the TestDisjointLinUCB obj's underlying member method code with example usage: obj.test_linucb_training_step() without return types