code: def test_padding_mask(self):
      layer = tl.PaddingMask()
      x = np.array(
          [
              [1.0, 2.0, 3.0, 4.0, 0.0],
              [1.0, 2.0, 3.0, 0.0, 0.0],
              [1.0, 2.0, 0.0, 0.0, 0.0],
          ]
      )
      y = layer(x)
      self.assertEqual(x.shape, (3, 5))
      self.assertEqual(y.shape, (3, 1, 1, 5))
      np.testing.assert_equal(
          y,
          [
              [[[True, True, True, True, False]]],
              [[[True, True, True, False, False]]],
              [[[True, True, False, False, False]]],
          ],
      )
  
imports: import functools
  from absl.testing import absltest
  import numpy
  from trax import shapes
  import trax.layers
  from trax.layers import test_utils
label_desc: Use image node_id 4 for calling the AttentionTest obj's underlying member method code with example usage: obj.test_padding_mask() without return types