code: def test_tostring(self):
      print(OnsetMeanEvaluation([]))
  
imports: from __future__ import absolute_import, division, print_function
  import math
  import unittest
  from madmom.evaluation.onsets import *
  from .None import ANNOTATIONS_PATH, DETECTIONS_PATH
label_desc: Use image node_id 3 for calling the TestOnsetMeanEvaluationClass obj's underlying member method code with example usage: obj.test_tostring() without return types