code: def test_cm(self):
      metric = ConfusionMatrix()
      cm = metric.result()
      self.assertTrue((cm == 0).all().item())
      metric.update(self.y, self.out)
      cm = metric.result()
      self.assertTrue((cm >= 0).all().item())
      metric.reset()
      cm = metric.result()
      self.assertTrue((cm == 0).all().item())
  
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 15 for calling the GeneralMetricTests obj's underlying member method code with example usage: obj.test_cm() without return types