code: def build_loss(self):
      return K.sum(self.output * self.output)
  
file_path: keras-vis/tests/vis/test_optimizer.py
imports: import pytest
  import keras.backend
  from keras.layers import Dense
  from keras.models import Sequential
  from vis.optimizer import Optimizer
  from vis.losses import Loss
label_desc: Use image node_id 2 for calling the _DummyLoss obj's underlying member method code with example usage: obj.build_loss() and returns: K