code: def check_call(self):
      loss = self.link(self.imgs, self.bboxes, self.labels, self.scale)
      self.assertEqual(loss.shape, ())
  
imports: import numpy
  import unittest
  import chainer
  from chainer import testing
  from chainer.testing import attr
  from chainercv.links import FasterRCNNVGG16
  from chainercv.links.model.faster_rcnn import FasterRCNNTrainChain
  from chainercv.utils import generate_random_bbox
label_desc: Use image node_id 2 for calling the TestFasterRCNNVGG16Loss obj's underlying member method code with example usage: obj.check_call() without return types