code: def start(self):
          
          if self._http_last_send is not None:
              raise RuntimeError('HttpMock has already been started')
  
          # 1) save request.Session.send in self._last_send
          # 2) replace request.Session.send with MockerCore send function
          super(HttpMock, self).start()
  
          # 3) save MockerCore send function in self._http_last_send
          # 4) replace request.Session.send with HttpMock send function
          self._patch_last_send()
docs: Overrides default start behaviour by raising ConnectionError instead
          of custom requests_mock.exceptions.NoMockAddress.