code: def test_delta():
      """test delta layer"""
      specgrams = np.array([1.0, 2.0, 3.0, 4.0], dtype=np.float32)
      specgrams = np.reshape(specgrams, (1, -1, 1, 1))  # (b, t, f, ch)
      delta_model = tensorflow.keras.models.Sequential()
      delta_model.add(
          Delta(
              win_length=3,
              input_shape=(4, 1, 1),
              data_format="channels_last",
          )
      )
  
      delta_kapre = delta_model(specgrams)
      delta_ref = np.array([0.5, 1.0, 1.0, 0.5], dtype=np.float32)
      delta_ref = np.reshape(delta_ref, (1, -1, 1, 1))  # (b, t, f, ch)
  
      np.testing.assert_allclose(delta_kapre, delta_ref)
  
imports: import pytest
  import numpy
  import tensorflow
  import tensorflow.keras
  import librosa
  from kapre import STFT, Magnitude, Phase, Delta, InverseSTFT, ApplyFilterbank, ConcatenateFrequencyMap, STFTTflite, MagnitudeTflite, PhaseTflite
  from kapre.composed import get_melspectrogram_layer, get_log_frequency_spectrogram_layer, get_stft_mag_phase, get_perfectly_reconstructing_stft_istft, get_stft_magnitude_layer, get_frequency_aware_conv2d
  from utils import get_audio, save_load_compare, predict_using_tflite
label_desc: Use image node_id 12 for calling a global function with example usage: test_delta() without return types