class_docstr: A mock class with implementation of abstract methods for testing.
code: def _compute_features(self, img: tf.Tensor) -> Sequence[tf.Tensor]:
      return [tf.random.normal(shape=(1, 8, 8, 3))] * 5
  
imports: import math
  import tempfile
  from typing import Dict, Optional, Sequence
  from unittest import mock
  from absl.testing import parameterized
  import tensorflow
  from mediapipe.model_maker.python.core.utils import loss_functions
label_desc: Use image node_id 2 for calling the MockPerceptualLoss obj's underlying member method code with example usage: obj._compute_features(img) and returns: unknown