code: def test_cpu(self):
      metric = CPUUsage()
      self.assertEqual(metric.result(), 0)
      metric.update()
      self.assertGreaterEqual(metric.result(), 0)
      metric.reset()
      self.assertEqual(metric.result(), 0)
  
imports: import unittest
  import torch
  from avalanche.evaluation.metrics import TaskAwareAccuracy, TopkAccuracy, AverageMeanClassAccuracy, MultiStreamAMCA, ClassAccuracy, TaskAwareLoss, ConfusionMatrix, DiskUsage, MAC, CPUUsage, MaxGPU, MaxRAM, Mean, Sum, ElapsedTime, Forgetting, ForwardTransfer, CumulativeAccuracy, LabelsRepartition
  from tests.unit_tests_utils import FAST_TEST, is_github_action
label_desc: Use image node_id 18 for calling the GeneralMetricTests obj's underlying member method code with example usage: obj.test_cpu() without return types