code: def test_pretrained(self):
      kwargs = {
          "n_fg_class": self.n_fg_class,
          "pretrained_model": self.pretrained_model,
      }
  
      if self.pretrained_model == "voc0712":
          valid = self.n_fg_class in {None, 20}
      elif self.pretrained_model == "imagenet":
          valid = self.n_fg_class is not None
  
      if valid:
          self.model(**kwargs)
      else:
          with self.assertRaises(ValueError):
              self.model(**kwargs)
  
file_path: chainercv/tests/links_tests/model_tests/ssd_tests/test_ssd_vgg16.py
imports: import numpy
  import unittest
  import chainer
  from chainer import testing
  from chainer.testing import attr
  from chainercv.links import SSD300
  from chainercv.links import SSD512
label_desc: Use image node_id 1 for calling the TestSSDVGG16Pretrained obj's underlying member method code with example usage: obj.test_pretrained() without return types