class_docstr: Mocks Faster RCNN Network
code: def loss(self, pred_dict, return_all=False):
      return tf.reduce_sum(pred_dict["w"], 0)
  
imports: import sonnet
  import tempfile
  import tensorflow
  from easydict import EasyDict
  from luminoth.train import run
  from luminoth.models import get_model
  from luminoth.utils.config import get_model_config, load_config_files, get_base_config
label_desc: Use image node_id 3 for calling the MockFasterRCNN obj's underlying member method code with example usage: obj.loss(pred_dict, return_all) and returns: tf