code: def test_list_trials(self):
      mock_list_trials = mock.MagicMock()
      expected_trials = {
          "trials": [
              {
                  "name": "1",
                  "state": "COMPLETED",
                  "parameters": [
                      {"parameter": "learning_rate", "floatValue": 0.01}
                  ],
                  "finalMeasurement": {
                      "stepCount": 3,
                      "metrics": [{"metric": "val_acc", "value": 0.7}],
                  },
                  "trial_infeasible": False,
                  "infeasible_reason": None,
              },
              {
                  "name": "2",
                  "state": "COMPLETED",
                  "parameters": [
                      {
                          "parameter": "learning_rate",
                          "floatValue": 0.001,
                      }
                  ],
                  "finalMeasurement": {
                      "stepCount": 3,
                      "metrics": [{"metric": "val_acc", "value": 0.9}],
                  },
                  "trial_infeasible": False,
                  "infeasible_reason": None,
              },
          ]
      }
      mock_list_trials.return_value.execute.return_value = (
          expected_trials
      )
      self._mock_discovery.projects().locations().studies().trials().list = (
          mock_list_trials
      )
  
      trials = self._client.list_trials()
  
      mock_list_trials.assert_called_once_with(
          parent=self._trial_parent
      )
      self.assertLen(trials, 2)
  
imports: from googleapiclient import errors
  import httplib2
  import mock
  import tensorflow
  from tensorflow_cloud.tuner import vizier_client
label_desc: Use image node_id 15 for calling the VizierClientTest obj's underlying member method code with example usage: obj.test_list_trials() without return types