code: def test_trainer_with_teststore():
      x = gluon.Parameter("x", shape=(10,))
      x.initialize(ctx=[mx.cpu(0), mx.cpu(1)], init="zeros")
      kv = mx.kv.create("teststore")
      trainer = gluon.Trainer(
          [x],
          "sgd",
          {"learning_rate": 1.0, "momentum": 0.5},
          kvstore=kv,
      )
      with mx.autograd.record():
          for w in x.list_data():
              y = w + 1
              y.backward()
      trainer.step(1)
  
      assert trainer._update_on_kvstore == False
      assert (x.data(mx.cpu(1)).asnumpy() == -2).all()
      # Expect exceptions if update_on_kvstore is set to True,
      # because TestStore does not support that
      invalid_trainer = gluon.Trainer(
          [x], "sgd", kvstore=kv, update_on_kvstore=True
      )
      pytest.raises(ValueError, invalid_trainer._init_kvstore)
  
imports: import mxnet
  import unittest
  import os
  import numpy
  from mxnet import gluon
  from mxnet.gluon import nn
  from mxnet.test_utils import assert_almost_equal
  from common import assertRaises, xfail_when_nonstandard_decimal_separator
  from copy import deepcopy
  import pytest
label_desc: Use image node_id 4 for calling a global function with example usage: test_trainer_with_teststore() without return types