code: def test_signature_on_ndarray(self):
      array = np.array([[2, 3, 5, 7], [11, 13, 17, 19]], dtype=np.int16)
      sd = shapes.signature(array)
      self.assertEqual(sd.shape, (2, 4))
      self.assertEqual(sd.dtype, np.int16)
  
file_path: trax/trax/shapes_test.py
imports: from absl.testing import absltest
  import numpy
  from trax import shapes
  from trax.shapes import ShapeDtype
label_desc: Use image node_id 3 for calling the ShapesTest obj's underlying member method code with example usage: obj.test_signature_on_ndarray() without return types