code: def test_PSNR_sanity(self):
      A = K.ones((10, 10, 3))
      B = K.zeros((10, 10, 3))
      self.assertEqual(K.get_value(PSNR(A, A)), np.inf)
      self.assertEqual(K.get_value(PSNR(A, B)), 0)
  
file_path: image-super-resolution/tests/utils/test_metrics.py
imports: import unittest
  import numpy
  import tensorflow.keras.backend
  from ISR.utils.metrics import PSNR
label_desc: Use image node_id 3 for calling the MetricsClassTest obj's underlying member method code with example usage: obj.test_PSNR_sanity() without return types