code: def store_instances(self, *args, **kwargs):
      return Instance()
  
imports: import os
  import tempfile
  import unittest
  from unittest.mock import patch
  from dicomweb_client import DICOMwebClient
label_desc: Use image node_id 3 for calling the MockDICOMwebClient obj's underlying member method code with example usage: obj.store_instances() and returns: Instance