class_docstr: Test if some models that were pretrained with APEX.
  
  They should load on CPU and GPU, even if the user doesn't have apex installed.
code: def test_fused_adam(self):
      with self.assertRaises(ImportError):
          # we should crash if the user tries not giving --opt adam
          testing_utils.train_model(
              dict(
                  model_file="zoo:unittest/apex_fused_adam/model",
                  task="integration_tests:nocandidate",
              )
          )
      # no problem if we give the option
  
      pp = ParlaiParser(True, True)
      opt = pp.parse_args(
          [
              "--model-file",
              "zoo:unittest/apex_fused_adam/model",
              "--dict-file",
              "zoo:unittest/apex_fused_adam/model.dict",
              "--task",
              "integration_tests:nocandidate",
              "--optimizer",
              "adam",
          ]
      )
      create_agent(opt, requireModelExists=True)
  
imports: import unittest
  from parlai.core.agents import create_agent
  from parlai.core.params import ParlaiParser
  import parlai.utils.testing
label_desc: Use image node_id 1 for calling the TestNoApex obj's underlying member method code with example usage: obj.test_fused_adam() without return types