code: def test_pad_for_frame(self):
      signal = np.zeros((10,))
      signal[0] = -1
      signal[-1] = 1
      frame_width = 4
      front_padded_signal = heuristics.pad_for_frame(
          signal, mode="front", frame_width=frame_width
      )
      framed = tf.signal.frame(front_padded_signal, frame_width, 1)
      self.assertEqual(framed.shape[0], signal.shape[0])
      np.testing.assert_array_equal(framed[0], [-1, -1, -1, -1])
      np.testing.assert_array_equal(framed[-1], [0, 0, 0, 1])
  
      back_padded_signal = heuristics.pad_for_frame(
          signal, mode="end", frame_width=frame_width
      )
      framed = tf.signal.frame(back_padded_signal, frame_width, 1)
      self.assertEqual(framed.shape[0], signal.shape[0])
      np.testing.assert_array_equal(framed[0], [-1, 0, 0, 0])
      np.testing.assert_array_equal(framed[-1], [1, 1, 1, 1])
  
      center_padded_signal = heuristics.pad_for_frame(
          signal, mode="center", frame_width=frame_width
      )
      framed = tf.signal.frame(center_padded_signal, frame_width, 1)
      self.assertEqual(framed.shape[0], signal.shape[0])
      np.testing.assert_array_equal(framed[0], [-1, -1, -1, 0])
      np.testing.assert_array_equal(framed[-1], [0, 0, 1, 1])
  
file_path: ddsp/ddsp/training/heuristics_test.py
imports: from absl.testing import parameterized
  from ddsp.training import heuristics
  import numpy
  import tensorflow.compat.v2
label_desc: Use image node_id 1 for calling the HeuristicsTest obj's underlying member method code with example usage: obj.test_pad_for_frame() without return types