code: def test_simple_call(self):
      layer = tl.CausalAttention(d_feature=4, n_heads=2)
      x = [
          np.array(
              [
                  [
                      [2, 5, 3, 4],
                      [0, 1, 2, 3],
                      [0, 1, 2, 3],
                  ]
              ]
          ),
          np.array([[[[1, 0, 1]]]]),
      ]
      _, _ = layer.init(shapes.signature(x))
  
      y, mask = layer(x)
      self.assertEqual(y.shape, (1, 3, 4))
      self.assertEqual(mask.shape, (1, 1, 1, 3))
  
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 1 for calling the AttentionTest obj's underlying member method code with example usage: obj.test_simple_call() without return types